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Any species returning to the land twice throughout their evolution?
Here's a question from my son I've found interesting enough to ask here. There are plenty examples of species returning back to the water environment, like dolphins, sea lions, walruses, some snakes, crocodiles etc.
The question is - are there any evidences that in evolution of certain species there was return to the land twice, that is, they've came from sea, then evolve as land species, then, again, evolved to somewhat marine or fresh-water and, finally, turn into land species again?
UPD Chordate are the most interesting but any example, even plants, would be nice.

What you describe in the last sentence is "returning to the water", not "returning to the land twice". What you mean is "water -> land -> water -> land", right?

Related: Has any flying creature evolved into a sea creature?

Are you interested exclusively in animals? Note that the absence of a clear definition of what is a "water species" and a "land species" might make it hard to answer.

I am sure that there are no animals that have gone from land to water, and then back to land. I am not sure about plants though. The transition to land is a very difficult one.  By the way, I would not say "returning to land twice", because they would only be "returning" once.

@KarlKjer Are you that sure. How about woodlice? Outside of animals, there are probably plenty of examples, esp. if we include prokaryotes but then again the question what it is to be a "land species" and a "water species" will matter

Yes, I am sure. Crustacians and Chelicerates evolved in water. I know that woodlice are both terrestrial and aquatic, but that does not necessarily mean the the aquatic species did not move onto land.

Crustaceans are paraphyletic, with insects nested inside them. The sister taxon to Hexapods is likely Remipedia, which are crustaceans that live in freshwater caves. So proto-hexapods evolved entirely on land. Not sure where myriapods evolved, but I would presume in water, because they are deeper on the tree than Hexapods.

Echidna is a good example, they came from platypus type ancestors aprox. 14-20 million years ago.

You list crocodilians as an example of animals returned to the water.  If so, there are extinct crocodilians such as Krabisuchus and Trilophosuchus that may have been more terrestrial, and would nominally be valid answers.  That said, crocodilians are too amphibious to find much satisfaction from answering this way.

Woodlouse
Life emerged in the water. Ancestors of insects, spiders, myriapods and crustaceans were probably terrestrial (please correct me if that is wrong) but then, crustaceans evolved to living in the water again. Finally, woodlice went back onto land!

Following your link in Wikipedia (and other) I wouldn't say that crustaceans appeared on land.

I did not say "crustaceans appeared on land" but "Ancestors of insects, spiders, myriapods and crustaceans [in other words, ancestor of all arthropods] were probably terrestrial". Again, I might be wrong. Can you please give me a reference stating that this ancestor was not terrestrial? From wikipedia > arthropoda, I could not find anything definitive but only that among the oldest fossils of arthropoda are marine and others terrestrial.

To hopefully resolve the question, I opened the post Were there any terrestrial species in the ancestry of all crustaceans?

Echidna come from platypus like ancestors about 14-20 mil years ago. so they count if platypus count as returning to water although not 100% of there like cycle.


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What causes plants in the prunus genus to reach anthesis?
In a related question, I ask how to trick fruit trees into flowering later in the spring by prolonging frozen ground conditions.
However, I'm starting to realize that I don't actually understand what triggers plants to flower in the spring in the first place. Possibilities include:

Photoperiodism
Air temperature
Soil/root temperature

It seems to me that this is a simple enough question. I'm guessing that plants in a certain genus would have a fairly specific genetic program that would stipulate when they should flower.
For example:
If root temperature is greater than X (for greater than Y duration), and daylength is greater than Z, then initiate flowering.
I'm not looking for the specific values (example x = 10 degrees C); the values would likely vary by species or even by plant. I'm just wondering what the primary variables are.

An answer provided by the University of Guelph Plant Sciences Department (they specialize in Malus):

Flowering of Malus and Prunus is driven primarily by air temperature. Provided sufficient winter chilling has accumulated for a given cultivar, tree growth and bud development will advance when air temps are above approx. 5 degrees Celsius. This process is irreversible. Once enough heat units (degree days) are accumulated, the flowers will open.
Flowering is a complex physiological process within the plant, driven by temperature. Photo-period likely does not play a large role in Malus.

Here’s how it works. Every morning when the sun breaks over the horizon — no matter what time of year it is — a clock starts ticking inside the trees. After a specific number of hours, the plants’ cells start producing high levels of a molecule known as the FT protein. This protein is responsible for initiating processes that help the plant grow.
But the FT protein has a curious property: In the absence of sunlight, it curls up and dies. So when the sun sets, it degrades rather quickly and becomes useless to the plant.
Nilsson thinks this peculiarity is the key to the seasonality of certain flowering plants, including most trees that blossom in the spring.
If a plant is genetically programmed to produce lots of FT protein starting, say, 13 hours after dawn, the molecule will be abundant during the last few hours of daylight in the longer days of summer. And those few hours are enough to kick-start crucial growth processes. So the cherry trees do most of the heavy lifting for the spring festival — bud and flower formation — way back in the summer and early fall.
As autumn progresses and the days shorten, that same 13-hour clock — the number of hours will vary by species and even by individual plant — means that the FT protein will be produced in darkness, and it will degrade before it can work its magic. The trees take this as a signal to drop their leaves and stop generating new buds.
When winter arrives, day length and temperatures both reach their annual nadir. At this point, the plant goes through vernalization, a dormancy period that has enormous importance in protecting the trees, for reasons explained below.
In springtime, one might imagine that the FT protein process would reverse: The days get longer, the FT protein is produced during daylight hours, and the plant kicks off its growth process. Surprisingly, that’s not what happens.
While the cherry trees recognize the arrival of winter by sensing a decline in daylight, they detect the arrival of spring based on temperature. They wait for what’s called a “temperature sum”— basically a bunch of warm days in a row. (The precise temperatures and durations required vary by plant.) When the temperature sum is reached, the blossoms open. Of course, since the National Park Service can’t control the weather, peak blossoming doesn’t always coincide with the Cherry Blossom Festival’s lighting of the stone lantern and the Japanese taiko drummers.
The cherry trees’ habit of marking the start of winter by daylight and the end of winter by temperature is reversed in some other plants. Plant biologists, for example, base much of their genetic research on Arabidopsis thaliana, or mouse-ear cress, a small plant that belongs to the same family as cabbage. (“It’s the laboratory rat of the plant world,” says Nilsson, because its small genome enables researchers to closely observe its genetically based behaviors. ) The plant measures the arrival of winter by a drop in temperatures and decides when to flower in spring by day length.
Click here for the source of this information, hope this helps :)
-Sartoaster

In continental countries winters can be very bright with latent fosts that kill flowers. FT is probably accelerated with high temps.

The University of Saskatchewan Plant Sciences Department builds on Guelph's answer:

In this context, my answer would be that photo-period definitely does
  not play a large role in Malus and Prunus.
Plants in these genera need
  their chilling requirement satisfied followed by temperatures high
  enough to allow growth to occur. Within reasonable limits, the higher
  the temperature, the sooner to bloom.
I have seen apple and plum trees
  that were neglected in a cooler room at 5 degrees Celsius form October
  to April reach anthesis with only enough intermittent/inconsistent
  light to produce barely a trace of anthocyanin and chlorophyll
  pigments.

From The Principles of Fruit-Growing By L. H. Bailey (The Rural Science Series):

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


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Can a gene be inactivated using CRISPR if it is not in the interspace of short palindromic repeats?
I have recently studied how CRISPR works but there is something that I do not understand at all. I have heard a lot of people claiming that with this method it is possible to modify any genome by inactivating, activating, removing or adding genes. However, as far as I have understood, DNA regions can only be modified if they are in the interspaces of short palindromic repeats. So, my question is whether a gene that is not in the interspace of short palindromic repeats can be modified or removed? And if it is possible to do so, how?

The CRISPR acronym was assigned when the system was discovered as a sort of bacterial immune system to kill viruses by storing parts of the viral DNA in the interspaced palindromic repeats. This was before CRISPR became a big deal for gene editing. But the name stuck. At least they didn't call it something like Sonic Hedgehog.

When people talk about genome editing with CRISPR, they are really talking about using CRISPR associated nucleases like Cas9 and Cpf1. These nucleases are useful since their sequence specificity is determined by a guide RNA and they can therefore be used to cut at specific sites in the genome. This actually has nothing to do with the repeats themselves.
See this answer for a brief overview of how genome editing with Cas9 works.

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Why are there exactly 207 morpho-electrical types of neurons?
I'm taking an introductory neuroscience course online, and it mentions that of the 55 morphological types and the 11 electrical types, there are 207 morpho-electrical types.  How does this work?  55 times 11 is 605, so it's not a simple mapping of 1 to 1. 207 isn't a factor of and doesn't share any proper divisors with 605, but it's roughly 1/3 (but not exactly). I don't see how a third makes sense though.
What causes exactly 207 morpho-electrical types?
Feel free to let me know if I should move this to Health or Psychology.SE, I'm not quite sure where to post this.

Was there a citation for this number? I definitely don't think this is a settled conclusion.

@Seanny123 No, but this paper was co-published by the same author and seems to mention that number.

I would add those references to your question since they seem quite relevant.

This is just that one author's opinion - it is telling that both sources you have for the number come from the same author. Henry Markram has a leadership role in the Blue Brain Project, a project to create a very detailed computer simulation of a chunk of neocortex to answer various questions. In the context of this project, it is somewhat necessary to make some decisions about numbers of cell types so that they can be incorporated in the model. People can bicker all day long about which types are actually unique types, though.
As far as the mathematics of having 55 morphological types and 11 electrical types, yet only 207 morpho-electrical types rather than 605, the answer is that the matrix is sparse. To get 605 types, you would need to observe all 11 electrical types within each of the 55 morphological categories. If not every electrical type is observed for a given morphological type, you will have less than 605 total. In some cases morphological types are specifically associated with particular electrical types.
You should also read about the concept of lumpers and splitters - in summary, in any context of classification without clear distinctions, different people will come up with different boundaries. It isn't really possible to argue "right" versus "wrong" in this context, because doing so requires weighting different values. Lumping may be beneficial for the sake of simplicity and generalization but miss some details; splitting may allow for more nuance but also risks not seeing "the forest for the trees."


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Why is the head/neck of the femur at that 120-150 degree angle?
I'm just wondering why the femur is such that there is that head and neck sticking out of the top at an angle, why it isn't just straight up into the hips?

The answer to this great question lies in understanding the "Hip Index". I am afraid I will have to go into some technical details to explain this:

When we stand on one leg, the hip abductor muscles on that side have to work hard to keep the pelvis stable and prevent it sagging. In this case the femur is static and the hip abductors are actually working on the pelvis that tilts up or down around the hip centre of rotation. The abductors are represented as "Fm" in the diagram.
In order to do so, the hip abductors have to exert more force than the actual person's weight. This is because the length of the effective lever arm of these muscles "distance h linking H1 with the hip centre H" is shorter than the opposite lever arm "distance D between H and G representing the vertical line down from the centre of gravity".
The hip index represents the mechanical disadvantage of the abductor muscles and is around "2/1" in normal individuals. Therefor if the person's weight is 70kgs, then when they stand on one leg, the hip abductor muscles on that side are contracting at 140Kgs to stabilise the pelvis, and the person's own weight is pushing down at 70kgs from the other side, resulting in the head of femur coming under 210kgs of weight.
If the neck of femur angle becomes more straight as in your question (approaching 180 instead of the average 135), then the hip index goes up towards infinity due to the reduction in distance "h" which approches zero. This is a deformity called "Coxa Valga". If the opposite happens and the neck of femur angle becomes less straight (less than 120), then although the mechanical advantage of the abductor muscles improves, this is offset by the reduction of the actual length of the abductor muscles "distance from i to T", making the muscles weaker. This condition is called "Coxa Vara". In reality, Coxa Vara in humans is also associated with shortness of the neck of femur, which reduces the length "h" also resulting in an increase in the hip index, and an increase in the forces over the head of femur in spite of the abductor muscles becoming weaker.
Both conditions "Coxa Vara and Valga" result in the hip abductor muscles becoming less effective in stabilising the pelvis. In these conditions, the hip index can go up to 4-6/1. This means that a person weighing 70kgs could eventually end up with over 400kgs on the head of femur, leading to pain and early wear and tear. It also results in the pelvis sagging down when walking, which leads to an abnormal walking pattern called "Trandalenburg Gait".
Therefore, a neck of femur angle of about 135 degrees provides optimum conditions for the minimum possible hip index without compromising muscle length and power. Any variation results in reduced abductor muscle effectiveness, gait problems, increased hip joint wear and tear and eventually pain.

Then what about the knee? In my rookie eyes, the situation around the knee is pretty similar to the hip, yet the angle is 180' there.

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Help in identifying crusty formation on Eucalyptus leaves
I am working with the plant species Eucalyptus perriniana (spinning gum) for one of my research projects. A few days into the experiment, I noticed some crusty deposits forming on several leaves (as shown in the attached photographs). I was wondering if anyone here might be able to identify it. I am not sure if the deposits are biological in nature, or if they are some kind of chemical precipitate.


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Book on current state of knowledge on the genetics of intelligence
I'm looking for a book that gives a good summation of the current state of knowledge on the genetics underlying intelligence.
I have read textbooks on human population genetics but I'm looking for something more specific.
I'd be happy for pointers to any books on neuroscience, developmental psychology, genetics that give some coverage to this topic.
I am not really looking for a popular science book.

Are you more interested in population and evolutionary genetics of intelligence or more on the molecular genetics of intelligence?

I believe that all of these aspects are pertinent, but I am probably more interested in research that point to molecular genetics and neurophysiology.

If it doesn't have to be a book, but could also be an extended review article, one possibilities would be: Toga et Thompson, 2005 ( http://www.annualreviews.org/doi/abs/10.1146/annurev.neuro.28.061604.135655 ) or Deary 2012 ( http://www.annualreviews.org/doi/abs/10.1146/annurev-psych-120710-100353?journalCode=psych)

Yeah, sure. Add those as an answer.

For current overview-like texts of diverse research topics the "Annual Review" series provides a good oversight:
Toga et Thompson, Annual Review of Neuroscience, 2005: GENETICS OF BRAIN STRUCTURE AND INTELLIGENCE
Deary, Annual Review of Psychology, 2012: Intelligence
For a very recent (and good) primary research study, - that will thus within its introductory paragraphs contain one very concise summary of the most current state of the field - one recommendation would be:
Sniekers, Nature Genetics, 2017: Genome-wide association meta-analysis of 78,308 individuals identifies new loci and genes influencing human intelligence

Thanks for that info that's exactly the kind of thing that I was looking for.

A very recent review has been written on this. See
Plomin, von Stumm (2018): The new genetics of intelligence.
For some of the latest genome-wide association studies, see:
Hill, et al (2017): A combined analysis of genetically correlated traits identifies 187 loci and a role for neurogenesis and myelination in intelligence.
Savage, et al (2017): GWAS meta-analysis (N=279,930) identifies new genes and functional links to intelligence.
However, as Robert Plomin and Sophie von Stumm report, newer genome-wide association studies are on the way which account for a larger portion of the variance. So there is constant progress at the moment.
If you're interested in the neuroscience aspect of intelligence, I recommend Richard Haier's book The Neuroscience of Intelligence.


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What is a "segregating gene"?
What does the term "segregating" mean in references like the following:
"found 42% of a random sample of loci to be segregating"
"15 blood group systems are known to be segregating"

If, at a locus, you have several alleles, then this locus is said to be polymorphic or segregating.
A segregating locus is just an untintuitve name for a polymorphic locus.

But on a locus that is "segregating" what would be the "segregating allele"? Is it the one that is the "mutated allele" or the one that differ from the reference genome? Basically, how to know which one of the multiple alleles is the one "that segregates"?

I would assume that a "segregating allele" would be any allele at a segregating locus. My general feeling is that in a context this kind of expression quickly become very clear.

So in this case: "The segregating alleles that account for genetic variation in height may be the same in females and males, but in females they act in the context of a developmental plan that results in a smaller adult height." does that mean that polymorphic alleles (or the alleles that make the site polymorphic) account for genetic variation? Basically, is it possible to have segregating alleles that do not account for genetic variation? The quote is from Hartl, D. L., and A. G. Clark. 2007. Principles of population genetics. 4th ed. Sinauer P.419


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What organism has the longest Hayflick Limit?
Assuming I am understanding the concept correctly, Hayflick Limits are reflective of a cells capacity for stable division. Additionally, the Hayflick Limits of various organisms differs.
My question is, what organism has the longest Hayflick Limit? I know humans have one ranging from 40-60, just to give a bit context.

The Hayflick limit is generally associated with telomere length. Human telomeres are a little on the long side as species go, but are not extraordinary. Many species of mice, and other rodents, have far longer telomeres than humans, for example, and obviously have much shorter lifespans. There's also such a thing as a "mega-telomere", found in a number of bird species, which can hundreds of times longer than human telomeres.
There's only a vague correlation between telomere length and a species' lifespan.  See Comparative biology of mammalian telomeres: hypotheses on ancestral states and the roles of telomeres in longevity determination for a starting point.  Telomeres are a part of the longevity story, but probably a fairly small part.
That said I don't see an explicit statement that those species with very long telomeres have a higher Hayflick limit. I assume this is because the Hayflick limit is an ultra-simplistic and not very useful description of a very specific set of conditions, but I don't know that for sure.

You rightfully point out that long teleomeres do not necessarily implicate a big Hayfilck limit. But the original question was "what organism has the longest Hayflick Limit?" and I'm still waiting for an answer to that.

Testing the Hayflick limit is extremely tedious and expensive (hundreds of cell passages may mean  years of lab time, maybe thousands or tens of thousands of dollars worth of lab equipment) and has little biological interest today. It's unlikely there's going to be any kind of comparative study, so this is probably as good as you're going to get.

I don't understand the link between telomere and lifespan: why do longer telomeres give shorter lifespan? It should be the opposite, isn't it?


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Does severing the Corpus callosum, effect the brain's communicating ability?
With serious epileptic seizures, a treatment is to sever the corpus callosum, which stops the seizures. However, does this affect the communicating ability between the two hemispheres? Or how does this affect the brain differently? What are the consequences in the brain?
Thank you in advance! (If I've got this all wrong, please let me know.)

Yes, it does; the corpus callosum is a major communication pathway between the hemispheres. Severing the corpus callosum is only done when seizures are severe enough to warrant it, and other options are ruled out for various reasons.
The condition of having a severed corpus callosum is often referred to as being a split-brain patient. There are some individual differences between patients, but hopefully searches using the keyword "split-brain" can help you find tons more information (summarizing it all here would give much too long of an answer).
One thing that is important to keep in mind is that although the corpus callosum is a very substantial connecting pathway between the hemispheres, it is not the only one, so the hemispheres are not completely severed. The cortex also communicates substantially with other brain structures that are not directly impacted by severing the corpus callosum.


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What kind of spider is this and is it poisonous?
 A brown furry diamond shape on its back and brown joints all on black body. Caught entering my house in Trinidad (small island off South America) -- killed the first one, this is the second.

Can you provide any information about where it was observed and if it was wild?

All spiders are venomous. I suspect you mean deadly. We would need the location too.

It's in Trinidad, small country off South America. It is wild and I think it was regularly feeding on me.

It's a Mygalomorph spider, of the sort which are usually called Tarantulas.  This is told by the two long, upcurved spinnerets and the large, dish-shaped carapace, with the eyes clustered in a clump - looking rather like the disk of the USS Enterprise from Star Trek, if the command bump was placed near the front edge.  I'm not sure which species it would be, but the good news is that like almost all spiders, it's pretty much harmless to humans.  These guys do have large fangs, though, so if you got bitten by one, you'd feel it.  As far as I'm aware, the venom of South American species is no big deal, so the feeling of being poked by a big needle is likely to be the worst effect.  Presumably they were entering your house to hunt for the small animals which share your home with you - large insects, small mammals and lizards, maybe.  I'd post an image, but I'm not sure which tarantula this would be (not really being a tarantula guy), and you could probably do as good a job of searching the internet as I could.  However, here is a resource I was able to turn up with a short search:
ttfnc.org/livingworld/index.php/lwj/article/download/479/462
As I said, I'm not really a tarantula guy, and so am not confident as to a specific ID of this spider.  However, having been pressed for an image, there are in this article some images of a spider which may or may not be yours.  The images are, however, tarantulas from Trinidad.  You will need to page through to the end of the article to see them:
http://sciencepress.mnhn.fr/sites/default/files/articles/pdf/z2017n2a5.pdf

Please provide evidence/support/citations for claims made as answers. Otherwise, we're no different from yahoo answers, which nobody should trust :p.

This is Holothele longipes (Trinidad dwarf pink tarantula) (formerly named Holothele sanguiniceps). It is found in a number of countries, including Trinidad and Tobago.

It is one of the smaller tarantulas, just a few inches long at full size.

(photos and map from GBIF: https://www.gbif.org/occurrence/gallery?taxon_key=2153490 )
It is identified by having no markings, black legs and palps which can shine blue, and red-to-brown thorax and abdomen with many red-to-brown hairs.


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Insect identification: Fly with eye strip

Location details:
Country - India,
State - Tamil Nadu,
District- Chennai.
Found this fly in my backyard keen to know its exact name. Thanks for the help

Please provide your geographic location. Thanks.

The antenna seen here is not that of Scathophaga (which would have a strong bristle at the front base of the last segment); I'm thinking Tabanidae, but not knowing where the photo was taken IS a huge handicap (from the OP's handle, perhaps Indian subcontinent?).  Another photograph showing the rear end of the critter would be nice as well (but probably impossible; I'm sure the animal is no longer available).

@ArthurJFrost side view & additional pics added.

@Charles location details added.

@Ναείστεαισιόδοξοι The large space between their two eyes doesn't match up with fly you mentioned and any link can be provided will be useful to confirm this species.

Looking at the bottom photo the way the wings are held and the spines coming off the scutellum (the white plate just before the wings) now suggests to me the family Stratiomyidae (Soldier Flies); having no detailed knowledge of the Indian fauna of that family forbids me from speculating further.

Definitely Stratiomyidae, probably genus Odontomyia. Very widespread and species-rich genus.
Here is an example of Odontomyia - not the same species - https://www.flickr.com/photos/63075200@N07/sets/72157632905103705/.

Can you add a source, an image and explanation why you think this is correct? As if now it's just a comment really.


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How did mosquitoes expand their habitations to a place they never lived before?
So, in the region I live, we have some sort of like a "mosquito zone", spanning for thousands of Kilometres, this is the place where you will normally find lots of mosquitoes, and this has been so for years and years. But last year, we were surprised to see that the mosquitoes have "invaded"a village which has never experienced them even once. The village though, is at the border with what I call "mosquito zone" but never has these insects "visited" this village. So I became curious to know, what has happened so that the mosquitoes said "now let's invade this village and live there"? I can't see anything suspicious that has changed. Do we have any explanations?

It could be a number of things. Mosquitos need standing water. Look for that. Any changes? Was last year particularly rainy?  One group of mosquitos lays its eggs at the waters edge. They lie dormant until the water reaches them again. If the water was high when the eggs were laid, then recedes, it may be years before the water reaches them again and the eggs hatch, resulting in a bloom of high numbers. Also, other mosquitos breed in containers. Things like tires, or coffee cans, or flower pots in cemeteries. Even a small amount of stagnant water in a container can result in mosquitos. Any changes there? The obvious change is the warming climate, but I would look first to changes in the water.


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Required energy to metabolize fat
Tl;dr: What is the net joule value of fat if used for energy provision, compared to e.g. carbohydrates. So does 1 Joule Fat intake result in 1 - X Joule energy provided to the cell, or does it work in a completely different way?

My understanding is that if I take in one Joule of fat, my body takes in the energy to move ~100g of mass up by one meter (Wikipedia).
Now for my body to use that energy, it needs to convert it to some sort of Glucose, right?
From the Lipid Metabolism Wikipedia Article I get that my fat needs to become a Triglyceride to serve as energy source.
There are some steps involved, roughly the following:

gastric peristalsis (basically muscle contractions to mix it all up)
peristaltic contractions in the gut (again, mixing is key)
lipase, also working in the gut to finally create Triglyceride
then the fat gets "packaged" in Chylomicrons and put into the bloodstream

releasing energy to the cell involves the following

Lipase unpacking the Chylomicrons
Splitting of the Triglyceride in Glycerin (the stuff we want) and fatty acids

Now this seems like a really cumbersome process to me, and I wonder what the net Joule Value is that arrives at the cell.
Is it significant, or is this process so efficient that it doesn't matter anyways?

"the energy to move ~100g of mass up by one meter", so you are interested in mechanical energy output. For energy as such does not change. On the level of biochemistry, perhaps the interesting question is how much net ATP is gained, and how much mechanical energy can be gained from that. And, no, I'm not an expert but just like you waiting for one to come along.

@Gyro Gearloose: Okay, that makes perfect sense. As soon as I am home I will try to rephrase the question more specific. I have never had any deeper chemical / biological education, just starting to get an overview over the terminologies...

I'm not so sure about the balance, but you need some heat to function. Fat might generate a bit more "waste" heat, leaving less to use for mechanical purposes, but perhaps glucose is so efficient you actually just need to burn a bit of it to keep warm. Also keep in mind that also the digestion of glucose needs several of the steps you mention, and nutritional energy content is the chemical energy content with some correction factors, perhaps already including the factors you mention.

So, what I was looking for, but was lacking the knowledge of, was the concept of "Thermic Effect of Food"
I really didn't know how to phrase my question well, due to the fact that I tackled the problem from the wrong angle.
Direct quote from the Wikipedia Article as it answers the question best:

The thermic effect of food is the energy required for digestion, absorption, and disposal of ingested nutrients. >Its magnitude depends on the composition of the food consumed:
Carbohydrates: 5 to 15% of the energy consumed [7]
Protein: 20 to 35% [7]
Fats: at most 5 to 15 %[8]


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Which bird species/families worm-dance and is this learned behaviour?
Today I saw a Herring Gull and a Common Gull (UK common names) "worm-dancing" on an area of wet grass. Worm-dancing is when the bird taps its feet on the ground rapidly in order to drum worms to the surface (that its a worm hunting behaviour might be conjecture, I'm not sure it's been proven).
Shortly after, a pair of Jackdaws landed and also began hunting, but without dancing. They walked over the area poking about in the grass, whereas the gulls stayed in the same place.
So my question is firstly, which species/families has worm-dancing been observed in, and secondly is this thought to be learned behaviour (this might be determined by it being a local phenomenon in certain populations)?
EDIT: Originally misidentified a common gull as a black headed gull (corrected above). Today I saw a black headed gull alongside the two larger gulls, and it was hunting like the jackdaws, not worm-dancing. There might possibly be a size/weight requirement to be able to worm-dance effectively, if we accept the hypothesis that it's a method of bringing worms to the surface.

Thrushes (Turdidae), like the Blackbird, don't actually dance, but they hop around when hunting worms. This might have the same effect as dancing.

Short answer
Sea gulls indeed tap the ground to surface earth worms, which is known as worm charming. Traditional human societies have practiced a similar technique known as worm grunting, involving vibrating the ground. Worm grunting is obviously a learned behavior passed down for generations in Florida. In other animals, such as gulls, I wasn't able to find evidence whether it is learned or innate behavior.
Background
From wikipedia:

Worm charming is especially [observed] among birds. The methods used vary; however, tapping earth
  with feet to generate vibrations is widespread. One common example is
  the "Seagull dance". The wood turtle also seems to be adapted for worm
  charming, as it is known to stamp its feet – a behavior that attracts
  worms to the surface and allows the turtle to prey on them.

It is popular belief says that the charming mimics the drumming vibrations made by rain and that worms are attracted by it. However, studies have indicated that the charm vibrations sound similar to those made by burrowing moles, a voracious worm predator and that the charming behavior of worms surfacing reflects an escape behavior of worms, namely the abandoning of their safe burrows to expose themselves to the real danger once surfaced (Catania, 2008).
The authors investigated the charming reaction of the worms by studying human-indiced charming, a technique used by fishermen. For generations, many families in and around Florida's Apalachicola National Forest have supported themselves by collecting the large endemic earthworms (Diplocardia mississippiensis). This is accomplished by vibrating a wooden stake driven into the soil, a practice called “worm grunting”. This worm grunting is obviously learned behavior.
However, I couldn't find evidence whether the worm charming in birds and turtles is learned yes or no.
Reference
- Catania, PLoS ONE 3(10): e3472

Do you have any information on which species/families practice worm-dancing, which was the main part of the question?


text:
Are there examples of cells with more than one nucleus?
I've always wondered why cells have only one nucleus, as having multiple would seemingly prevent mutation. Are there examples of organisms with multiple nucleuses? If not, is there a reason?

From a certain standpoint, your own cells have more than one nucleus, in the sense that they contain mitochondria.

Are there examples of cells with more than one nucleus?

Yes, they are called Multinucleate cells. There are two types of multinucleated cells

Syncytia
Coenocytes

I highly recommend having a look at this answer for the definitions.
Examples of Syncytia include

Osteoclasts
Skeletal muscle fibers (thanks @kmm)

Examples of Coenocytes include

Codium (Thanks @GerardoFurtado; see picture below)
Blastoderms early in the development of a fruit fly

Are there examples of organisms with multiple nucleuses?

Side note: The plural of nucleus is nuclei
In many fungi, during sexual reproduction, a fusion of cytoplasm happen early in the mycelium but a fusion of the nucleus happens only very late (just before sporulation). This is a type of Coenocytic mycelium. In these species, non-negligible fractions of their cells are multinucleated.
There are endosymbiotic and endoparasitic eukaryotes in other eukaryotes that would result in a cell containing several nuclei but that would not count I would guess as the nuclei belong to different species.

Picture of Codium. The entire algea is a single multinucleated cell.

"I doubt there are species where all cells are constantly multinucleated"..  except for the gamete phase, that's exactly the situation for several species of algae and protozoa, in which all cells are always multinucleated (+1 though).

Also, the way you created your list may not be very didactic to a layman: all multinucleate cells are either a syncytium or a coenocyte. There is no other category. However, in your list, it seems that there is more... For instance, skeletal muscle cells are syncytia. have a look at my answer here: https://biology.stackexchange.com/a/64439/24284 . I'm seeing that the mistake is from the Wikipedia page you shared: osteoclasts are syncytia.

There is a branch of life called the Diplomonads, most of which have two nuclei. They are single cell organisms and an early offshoot of the eukaryotic linage. A good example is Giardia lamblia.
https://en.wikipedia.org/wiki/Diplomonad
Giardia lamblia

According to this article The hairy beast with seven fuzzy sexes
Tetrahymena thermophila has two: a large macronucleus and a small micronucleus. The macronucleus controls the everyday functions of the cell, while the micronucleus deals with its complicated sex life. In fact this is true for all ciliates.

When a "slime mold" enters the "plasmodium" phase n cells merge together to form one cell with n nuclei.  This means plasmodiums can have thousands or tens of thousands of nuclei...

Skeletal muscles (striated) are multi-nucleated-have more than one nucleus per cell as they are formed as a result of the fusion of myoblasts.
Reference-   Skeletal Muscle: Form and Function (2006)
By Brian R. MacIntosh, Phillip F. Gardiner, Alan J. McComas


text:
Is Ellman's reagent specific for low molecular weight proteins and thiols?
Is it still possible to quantify cystein rich low molecular weight proteins such as Metallothionein in a given sample using Ellman's reagent if the sample is contaminated with some high molecular weight proteins?

It's specific for thiols in general. If the contaminating proteins contain solvent accessible thiols, DTNB will react with them.

Doesn't even need to be a protein. People in my lab often make large polymers with some thiol modifications. The thiols are quantified with Ellman's Reagent.

@user137 Yes certainly; I confined my answer to the question.

@canadianer How can we determine if the contaminating protein contains solvent accessible thiols?

@k.shekh First of all, it should be rather trivial to purify your low molecular weight protein from the contaminating high molecular weight proteins. I think that by far would be the best solution. If for whatever reason that’s not possible and you know the identity of the contaminating proteins, you can search the literature (including primary protein sequences) for information on the cysteine content. If the identity is unknown, you would need to make the determination yourself. I have had success labelling thiols with maleimide conjugated fluorophores and then visualizing them in a gel.


text:
Except for protecting ears from cold air, does a woollen cap provide any other significant advantage in winters?
I have woollen earmuffs and they are really comfy. They do the job of protecting ears well enough and I don't really have to worry about hair statics as they only cover ears and not my hairs. But many times I do get advice against using those earmuffs and wear a woollen cap instead.
If protecting ears is the only reason of wearing caps than I don't think i should leave my earmuffs but most people, though unknown of any scientific proof, claim that caps have more of a advantage than just that. Is it really so?

I've never seen woolen headphones, and have a hard time imagining them, but there is a lot of practical iinformation about the value of insulating (not necessarily wool) head coverings, and their value in heat retention.  Of course it depends: for instance, if you have a thick head of long hair, a hat is going to be of less value than if you're bald.

Well I suppose that you are imagining some music type headphones with made out of wool. That's not it. They are just like a cap except that they don't cover your head, just your ears.

If you mean something like this https://www.amazon.com/Fleece-Ear-Muffs-Warmers-Earmuffs/dp/B01LZGPNAI they're called earmuffs, not headphones.  They keep your ears warm: a cap will keep the rest of your head warm, too.  And if it's really cold, you can wear both :-)

Oh, thanks for the correction. Never knew their actual name, even the shopkeepers in my region didn't!

This article is what you need: http://www.bbc.com/future/story/20130708-is-most-heat-lost-from-your-head . Citing an excerpt from it:

[H]aving your head immersed in cold water only adds 10% to your overall heat loss in a cold pool. And given that the head accounts for 7% to 9% of the body’s surface, that doesn’t seem excessive.
But before you throw your collection of woolly hats in the bin, there’s another finding to bear in mind: when the head is allowed to get cold and the body is effectively insulated, the body’s core temperature drops a lot more rapidly than most people would expect.

In the end, wearing a woollen cap prevents the body's core temperature to drop too low. So if the rest of your body is well covered, you can skip the cap and put just your comfy headphones on; if, on the other hand, your clothes don't protect you well, putting a woollen hat on may be the easiest way to not feel cold.


text:
In the transition to multicellularity what function becomes specialized first?
It's my understanding that in the transition from single celled to multi-celled organism a lineage will transition between stages where existing in a colony of cells is optional to one where it is obligate. Integral to this process is the parts of the colony taking on specialized roles in the colony's survival. First is tissues, and eventually full blown organs.
With that as background (please correct any misconceptions), which job tends to be taken over by specialized cells first in the transition? The three main ones in every multicellular organism I can think of are: digestion, structure (including skin and any rigidity), and reproduction (please suggest roles if I missed any, or over-included). Is there a single answer to this, or does it vary between lineages?

Lyons & Kolter (2015) On the evolution of bacterial multicellularity. Curr Opin Microbiol 24: 21-28; emphasis mine:

Multicellularity is one of the most prevalent evolutionary innovations
  and nowhere is this more apparent than in the bacterial world, which
  contains many examples of multicellular organisms in a surprising
  array of forms.
cell-cell adhesion to form a new evolutionary unit, and intercellular
  communication leading to coordinated activity (...) are the minimal
  requirements to redefine a group of cells rather than any single cell
  as an "individual."
[M]ulticellular magnetotactic prokaryotes (MMPs) [are the only known bacteria] without a unicellular phase in their lifecycle.
[The key features of multicellularity are: cell differentiation,
  intercellular signaling, extracellular matrix, tight cell-cell
  junctions, coordinated movement, division of entire structure (Table
  1).]


text:
Causes of the stochastic behaviour of voltage-gated ion channels
I came up with the following electro-mechanical model of a voltage-gated ion channel, resp. of its voltage sensor as described here and here. The voltage sensor is a bistable system with two local energy minima $E_1(V)$, $E_2(V)$, the first one indicating "closed", the second one "open":

From Bezanilla, The Voltage Sensor in Voltage-Dependent Ion Channels, p. 567. You can interactively explore a voltage-dependent energy surface here (schematically).
I created a spring model with Algodoo which looks like this (green: the voltage sensor (= a peptide subunit), white springs: keep it in place, blue: favours the closed state, red: simulates voltage, opens the gate):

(You can download the model here and explore it interactively with Algodoo.)
To behave stochastically - i.e. the probability of being open $p(V) \sim e^{-\Delta Q(V)/kT}$ which presupposes a thermal equilibrium - there must be fluctuations that can lift the system above the energy barrier between the two energy minima.
My question concerns the source of these fluctuations in the real ion channel: are these thermal (mechanical) fluctuations (e.g. other molecules hitting or tearing the sensor) or are these fluctuations of the membrane potential?

And I'll note that this isn't something special with ion channels, it's true of many other types of proteins as well as non-biological molecules.

My model definitely does have (two distinct) energy minima, as can be seen by just watching it (above) or trying it out  (at Algodoo) or by checking the Geogebra link which reflects the Algodoo model. It's not about one spring, but about a system of springs that definitely may have different and distinct energy minima.

I don't understand your second comment.

Ah I'm sorry I missed the structure of your model entirely. You can disregard. My second comment was just to state that this isn't unique to ion channels; lots and lots of other molecules or proteins have the same sort of behavior where they switch between distinct states.

@BryanKrause: Do you have any idea concerning my original question: Do the random fluctuations stem more from the immediate molecular (mechanical) environment of the voltage sensor or from the membrane potential (which in turn stems from dendritic input/PSPs).

I believe it's from the molecular environment of the voltage sensor. I also think you have to consider spatial scale here; membrane potential is best thought of at a scale of an electrotonic stretch of membrane. Molecular interactions, on the other hand, are much smaller, and at that level the precise spatial presence of individual ions could have some influence, but I wouldn't consider that "membrane potential." I personally have no idea whether that presence matters on the scale of molecular vibrations/temperature. From the perspective of neuroscience it doesn't matter at all.

Let us continue this discussion in chat.

The fluctuations arise form thermal energy and can be described by the Eyring equation


text:
DNA linking number, twist and writhe
The image below is taken from a molecular biology textbook.
It is not clear to me that what is happening at the two writhe crossings matches up with the numbers provided.
Is there  a problem with this example? And if not, is anyone able to explain (without using Calugareanu's Theorem, i.e. $\text{Lk}=\text{Tw}+\text{Wr}$) why the linking number is $23$? When I give the two strands orientations and half the sums of signs of crossings, I do not get $23$.

Does this answer help?

@canadianer I understand how to compute Lk, Tw and Wr, but I think the linking number in this particular example is not as clear as any of those in your answer, and I am seeking to verify whether or not this example is correct. I am having trouble around the two places where there is writhe. I am also using a different (but equivalent) definition of Lk - the one which gives  orientations to the strands and signs to the crossings, as seen on the wikipedia page here: https://en.wikipedia.org/wiki/Linking_number

Oh I see. Actually that picture is awful since it shows all four strands intertwined at the sites of duplex crossover (which is not what happens).


text:
What is the biological relevance of RIPPLE phase in membranes?
I was reading about ripple phase in bilayer lipid membranes which is described here as a meta-stable state between lamellar tilted crystalline and lamellar fluid state. It is also known that ripple phase exists just below the phase transition temperature $T_m$. The figure below is from this article.

I have 2 questions here:
1) Is ripple phase a stationary structure or does it propagate in space as a travelling wave? (Since they have crystalline structures inbuilt will the fluidy defect propagate?)
2) Secondly and more importantly will ripple phase gets exhibited above transition temperature $T_m$ if the lipid interacts with some molecules like protein etc?
UPDATED QUESTION:
What can be the possible biological significance of Ripple phase in membranes? Will formation of ripple in membrane initiate any relevant processes, since membrane curvature itself is changing? I will be really helpful for any resources related to this.
I am citing an experimental biological work related to Hsp12 protein interaction with DMPG membrane in yeast which reports ripple phenomenon well above the usual transition temperature. Paper here.

NOTE: I was initially confused about whether to post this in biology.SE or physics.SE. I got more tags here. So posting it here.

Mmmm odd. Anyway, this post is indeed Bio, physics and also chemistry related. What I would do is go to the respective sites, enter their chat and ask if it's on topic there. Cross posting is not OK, so I'd reckon if Physics accepts it, I can either migrate or you can repost and delete it here. Physical might be your best bet, but Chemistry might as well.

@AliceD I have modified the question a little bit and given a bounty. Do you want to have a look now?


text:
What is a good introductory book on plant genetics for an outsider?
I am interested in plant breeding, but my knowledge about plant genetics itself is unfortunately limited (math major). Would you know of any good introductory '101' books that explain the basic concepts? As elementary as: what exactly is DNA recombination? What is an F1, F2 plant?
Many thanks and kind regards,
David

I am in a PSEO class for plant biology and ecology and I found a book online I believe you would find useful.
Click here
I've used this book to study many times even though it wasn't supplied to me. It does a great job explaining overall concept of plant microbiology. This book will introduce concepts that someone would be new to. I recommend that you give it a read, then after you read it, move to a book specifically on plant breeding.
Hope this helped!
-Sartoaster


text:
What percentage of twins has the same gender
If 30% of all twins are identical twins, what percentage of twins has the same gender? I thought: all identical twins have the same gender so it’s at least 30%. And of the non-identical twins it’s about 50%. So 50+30=80%?? Correct me if I’m wrong..?

I agree that same sex twins account for about two-thirds. Note that this means that the naive hypothesis that the three possible configurations BB, BG and GG have equal probability gives the right answer!

You stated:

30% of twins are identical
50% of non-identical twins have the same gender

Therefore 70% of twins are non-identical and 50% of those will have the same gender. I'll leave the rest of the calculation to you.

So: 35+30= 65% of twins have the same gender?

@Mett123 Based on the information you gave, that would be correct.


text:
I found this on the beach at Breamlea in Vic Australia and wondered if you could tell me what it is please
It is about 6.5 x 5 centimetres and semi transparent.
It has quite a tough skin and is hollow inside. Like a tight clear tooth shaped balloon. I have put a coin next to it for you to see the size.

Dentist merchandise?

It's a swim bladder, probably a porcupinefish swim bladder. They can be found washed ashore still inflated. They've been described as "molar shaped". (Picture from Australian Museum.)

It's hard to tell exactly, but if I had to bet I'd say it's a small part of an algae called Neptune's necklace:

Some species are native to New Zealand and Australia. Where two "branches" split, the shape you found can be produced.
Looks like they're also found in your area: http://bie.ala.org.au/species/NZOR-4-7414


text:
Are mediterranean sharks shyer than ocean sharks?
I have been diving in the mediterranean for some time and have never seen a shark, heard of anyone seeing one or seen shark diving advertised. And still there are all kinds of sharks in the mediterranean. Why are they so hard to spot?
For comparison: There are a lot of accounts of people seeing sharks in for example the Maldives and other places.
Something like this would be unthinkable in the Mediterranean:
https://www.youtube.com/watch?v=Yg-dUPVzWiM

It’s not just the Mediterranean, but depending upon many factors, such as the species, typography, depth, current, and availability of food, your chance of encountering a shark in the wild changes, though generally through scuba or skin diving it is still rare.

@Sudachi sure, but I am talking about any sharks at all, not a specific species. I have never seen one in the Mediterranean, although they are out there. Sharks should be active somewhat near shore and in somewhat shallow water right? I have dived to 40m but have seen 0 sharks.

It really boils down to the species and the conditions. You are only able to cover a limited area and shallow depth and limited amount of time as a diver. Many species of shark are likely to know you are there before you know they are there and sharks can be shy and avoid divers. However certain shark spots can be popular feeding grounds, sleeping grounds, or mating areas. While I think there is a lot more historical pressure from fishing sharks in the Mediterranean, I don’t think there is anything innate about the sea there that makes all shark species there shy. I have heard of shark spots in Lebanon: http://www.nisd-online.com/article-101506-talesanddivesinlebanon.htm, though I do know the Red Sea offers a lot more in terms of shark encounters. There simply is a lot that goes into a shark encounter and we do not know nearly as much as we would like on their behavior. I’ve been on many dives in different parts of the world to see hammerheads in the wild and it can be a shot in the dark. It takes many years of local knowledge of the species’s behavior and conditions (season, tides, current, temperature, time of day, moon phases, undersea typography, etc). They are out there, but my best advice is to speak to fisherman and local divers, and also get creative in how you approach them (think about boat sounds, consider beach entries only, go in small groups, try early morning, try different seasons, etc.) Many scientists doing research on certain species in a locale find talking to fisherman to be a huge source of knowledge too.


text:
Homework - Genetics linkage problem

A farmer purchases f1 hybrid seeds. These seeds contain four heterozygous loci that give a significant increase in crop yield when compared to either homozygote. Two of these loci are on the same chromosome and show partial linkage. If the farmer allows the f1 plants to self-fertilize, what is the probability that a seed from the resulting f2 generation has all four heterozygous loci?

a) at least 1/2
b) between 1/2 and 1/4
c) between 1/4 and 1/8
d) between 1/8 and 1/16
e) less than 1/16
I think it's either d or e. For the first two genes (unlinked), there is 1/2 chance to get heterozygote. So, 1/2 * 1/2 = 1/4. For the next two linked genes, if they were unlinked, it would be 1/2*1/2 = 1/4 for a total of 1/16. But since they are linked, I'm thinking that the chance for heterozygote might be reduced, so maybe the answer is e) less than 1/16?? Not sure where to end, though...

Try to draw a Punnet square! If you have tried already, what difficulties have you encountered? What brought you to think the answer is either 'd' or 'e'?

I agree with your reasoning! If the two genes are perfectly linked, then the answer is $\frac{1}{8}$. If they are perfectly unlinked, then the answer is $\frac{1}{16}$. The answer therefore must be somewhere between $\frac{1}{8}$ and $\frac{1}{16}$.  Good job!
Of course the answer e) is pretty silly as any other answer ('a','b','c' and 'd') would yield to 'e' being necessarily true. So, if you have to choose only one, I would just go with 'd' and highlight that the answer 'e' is silly.

I still don’t understand how if the two are completely linked, the answer would be 1/8.

Let's consider that at both loci, we have two alleles A and B. Here is a representation of the first F1 individual
-------A----A-----
-------B----B-----
Here is a representation of the second F1 individual
-------A----A-----
-------B----B-----
Of course, they are the same as the parental lines are pure breed. Now, if the two loci are perfectly linked, then the offspring can have the following possible genotypes
-------A----A-----
-------A----A-----,
-------B----B-----
-------A----A-----,
-------A----A-----
-------B----B-----
or
-------B----B-----
-------B----B-----
, but the offspring cannot be
-------B----A-----
-------B----B-----
or an other combination requiring recombination between the two loci. Therefore the probability to be heterozygote for the F2 at two perfectly linked loci is the same as the probability to be heterozygote at one of these two loci (if we assume the mutation rate is negligible).

Why can't parents be: parent1: -------B----A----- -------A----B----- parent2: -------A----A----- -------B----B-----[?]

Because parental lines are pure lines. When we talk about an F1 generation, we talk about the hybrid between two pure line. By pure line, we mean that we got rid of all genetic variance. So, one parental line is fixed for the A alleles and the other line is fixed for the B alleles.  In other words here are the genotypes of the pure parental lines.
-------A----A-----
-------A----A-----
and
-------B----B-----
-------B----B-----
One parent can therefore only give
-------A----A-----
while the other one can only give
-------B----B-----
so, the F1 generation is therefore necessarily heterozygote at all loci.

I still don’t understand how if the two are completely linked, the answer would be 1/8. It would mean that in order for these two linked genes to produce a heterozygote, they would have a 1/2 chance to do so. Is this necessarily true?

Please see edit.

Why can't parents be: parent1: -------B----A----- -------A----B----- parent2:  -------A----A----- -------B----B-----

@LittleDragon Pleas see edit

Wow, speedy. So you're saying that all f1 parents must have the same alleles in the same order on chromosomes? If so, then I'll mark your response as the answer.

I am not sure why you are talking about ordering. I used the letters A and B at both loci but they are denoting the same alleles of course, they just denote that parental origin. See small edit, maybe it will help you out.


text:
Homework: Diffrentiate between 2 toads

How to differentiate between 2 toads one of them result of artificial parthenogenesis and the other from renucleation?

I answered that the toad resulting from artificial parthenogensis is identical to the mother
While the other toad which result from renucleation is identical to that which the nucleus was taken from
My answer is so unrealistic and I can't find any other answer so I though I could use some help.

Welcome to Biology.SE. What data do you have access to make the differentiation? What frog species? If you could explain what's your interest behind the question, it may help.

I recommend looking at the tags again

Oh indeed.... Is it the entire homework question exactly as phrased, or is there more information around it? I don't want to be pedantic but make sure to quote correctly. You can highlight a quote is a quote by starting the line with >

Sorry I am new  .The question is exactly as its phrased

No worries. It is part of being new to Biology.SE to have its post reviewed, corrected, clarified and sometimes closed. I edited you post. Please note that homework questions are allowed on Biology.SE only if the OP is displaying its attempt at answering the question. So, in its current form your post should get closed. Can you please add your thoughts about this question? On top of protecting the site from "do my job" type of question, it also allow us to understand what level of understanding the OP have and what is unclear for the OP.

Going to edit it now . Thx


text:
What are pit fields?
I found this statement from my biology text book,

"The sieve tube elements and the companion cells are connected by pit fields present between the common longitudinal walls".

Is the pit field same as Plasmodesmata ?

Pit vs plasmodesmata
From wikipedia > pit

Pits are thin portions of the cell wall that adjacent cells can communicate or exchange fluid through, utilizing plasmodesmata.

The definition of "pit" is therefore very related to the one of "plasmodesmata". From wikipedia > plasmodesmata

Plasmodesmata (singular: plasmodesma) are microscopic channels which traverse the cell walls of plant cells and some algal cells, enabling transport and communication between them.

I think the following quote (from wikipedia > plasmodesmata again) will help you to distinguish pits from plasmodesma

Primary plasmodesmata are formed when portions of the endoplasmic reticulum are trapped across the middle lamella as new cell wall is laid down between two newly divided plant cells and these eventually become the cytoplasmic connections between cells. Here the wall is not thickened further, and depressions or thin areas known as pits are formed in the walls. Pits normally pair up between adjacent cells. Plasmodesmata can also be inserted into existing cell walls between non-dividing cells (secondary plasmodesmata)

Pit field
A pit field however is just an area where there are plenty of pits! From Merria-Webster

[A pit field is] an area in the wall of a plant cell in which one or more pits develop

Pit field is thin depression in primary cell wall whereas pits are depressions in secondary cell wall. For example Companion cells and sieve tube elements are living cells having primary walls. They are connected by pit fields. Note that pit fields are also characterised by presence of plasmodesmatal connection.

Welcome Mudasir, in addition to the advice in the answer banner, you should take our wonderful [tour] and refer to the [help] as and when for guidance. Enjoy the site.


text:
Is there any possibility that gender is determined by Temperature?
One day I was watching TV show. It was based on Fire Dragon. They stated that if the dragon provide greater warmth to the egg, then a male Dragon will hatch. And if the Dragon provide less warmth to the egg it will be female Dragon.
This was totally Science Fiction!!
But is there any possibility that, the Temperature decides the Gender of progeny.

Not exactly a duplicate but the answer to this question is in the background of the linked question.

It is definitely more than science fiction. Many species have sex determination that depend upon the temperature.
As a rule of thumb, when it comes to sex, not much has been invented in fictions. The diversity of reproductive system is HUGE! I will not mention 1% of the existing complexity in sex systems. For simplicity, below I will limit my concepts and examples to big animals only. I won't talk about

double fertilization
cloning
parthenogenesis
dosage compensation
Mating types
Cases of multinucleated cells typically in fungi but not only
Asexual reproduction
Systems with more that two genders or with coexisting hermaphrodite along with a single other gender
Liability factor
Reaction norms for sex determination
How reproduction relate to all that
How dosage compensation relate to all that
How the concept of individual relate to all that
etc...

Sex Determination System: GSD vs ESD
There is a great diversity of sex determination system. The standard is to classify them in two

Environment Sec Determation (ESD)
Genetic Sec Determation (GSD)

Of course, the reality is more complex. In many species a mixture of both genetics and environment clues matter.
Within ESD species, there is quite a bit of variety. Some species use temperature (e.g. crocodiles, Nile tilapia, Australian skink lizard), others use social cues (e.g. clownfish, swordfish, boa constrictor).
Within GSD, there is also a great deal of diversity. By far not all species use the XY system used in mammals.
Related post

Do males of all sexual species have Y chromosomes?
Have there been any theories put forward as to the reasons behind Temperature-Dependant Sex Determination in reptiles?


text:
How do alcohols and aldehydes destroy the plasma membranes of bacteria?
I am interested in knowing why a 60-80% solution of alcohol (usually ethanol or 2-propanol) can effectively kill vegetative bacteria and fungi. I know that it can coagulate essential proteins like enzymes but the process has never been explained to me.
I'm also interested in knowing how aldehydes like the polymerized form of glutaraldehyde inactivates proteins and nucleic acids. Could someone with any insight / knowledge share what they know?

Alcohols are dehydrating - they remove water from the cell. And since cells need water to survive, this is lethal to bacteria. However, in order to work effectively, an alcohol needs the proper amount of time to penetrate the cell membrane of the bacterium. If the percentage of alcohol is too high, it will evaporate before entering the cell. Too low, and it will enter the cell but not be lethal. 70% alcohol turns out to be the most effective concentration for use as a surface disinfectant with many different types bacteria.


text:
Are mesophyll cells the same as parenchyma cells?
I read in my biology textbook that ground tissue is constituted by parenchyma, collenchyma and sclerenchyma.It was also mentioned that, in leaves the ground tissue was made up of thin walled chloroplast containing cells called mesophyll cells.

Despite countless sites and other resources saying otherwise, Mesophyll is not a tissue technically speaking. It's just a place, a specific area. Or you can even think of it as the set of all tissues in a given area.
And that given area is easy to define: the "filling" of the leaf, between the upper and lower epidermis. According to Mauseth (2012), that with Raven is my favourite book on Botany:

Mesophyll: All tissues of a leaf except the epidermis.

Actually, this is easy to see if you understand the Greek origin of the term: μέσος, meaning "in the middle", and φύλλον, meaning "leaf". Therefore, mesophyll means "in the middle of the leaf".
In a common, regular leaf, most of the mesophyll is made of parenchyma, be it palisade or spongy. As I said before several sources treat these terms (mesophyll and parenchyma) as synonyms, but they are not.
Just for completeness, this is a very simple list of the plant tissues. You'll see that mesophyll is not on it:

Meristems
Dermal tissues

Epidermis
Peridermis

Ground tissues

Parenchyma
Collenchyma
Schlerenchyma

Vascular tissues

Xylem
Phloem

Source: Mauseth, J. (2012). Botany. Sudbury: Jones & Bartlett Learning.


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What species of flying insect is this? Resembles a fly with the wings of a dragonfly
Locus: Vienna, Austria
Local Time : 12:24 today, 6th of January
Size: length approximately a large thumb. Width much smaller (pic).
Behaviour: possibly attracted by honey in my medicine, along with flies.

Definitely in Syrphidae.

Might be Episyrphus. In any case, the common name for the family is "Hoverfly".

@KarlKjer After consulting Wikipedia, I tend to agree. Furthermore, I am amazed to see that this kind of eyes apparently makes it a female! https://en.m.wikipedia.org/wiki/Episyrphus_balteatus

Insect ID from photos is difficult, but this is definitely in Syrphidae. The alternating thick and thin stripes on the abdomen resemble very much those in a picture I found here: https://alchetron.com/Episyrphus-balteatus
I would say that it is likely in the genus, Episyrphus, which is present in Austria.

Syrphidae are usually easily identified from photo. This is without a doubt E. balteatus. There is no other species that resembles it in Europe.

Could you provide further support using Comstock-Needham system out of curiosity?


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What problem does kin selection solve?
I'm trying to understand what problem led to a development of kin selection.
The explanations I've found consist roughly of the following:

The existence of some altruistic and cooperative behaviors in social
  insects like honey bees, the phenomenon of sterile castes formed by
  non-reproductive individuals that leave no offspring and the suicidal
  role of these insects in defending the hive, were traits that natural
  selection could not favor. Kin Selection | Nectunt

What I do not understand: Why could natural selection not favor the phenomenon of sterile castes?
From the perspective of the sterile worker: Since it can't reproduce, no strategy will affect the number of offspring it has (will always be 0). So there is no conflict with natural selection.
From the perspective of the queen bee: Her offspring consist of sterile worker bees and a new fertile queen bee. The worker bees improve the viability of the next queen bee. This is consistent with natural selection.
Therefore, I can't see the relevance of the worker bee sharing lots of genes with its sister queen bee. This seems to be nothing but an ancillary effect of the mechanisms of evolutionary change.
Imagine, the queen bee could produce worker bees without a genome (like a robot), or a genome that is not related to its sister queen bee, those worker bees would still show altruistic behavior.
What am I missing?

Why natural selection leads to selfishness
Imagine a population of individuals. At a given locus, some individual carry the A allele and some others can the S allele (A for altruistic and S for Selfish). For simplicity, we will assume organisms are haploid. Individuals carrying the S allele are selfish and will take care of themselves only. The A allele are altruistic meaning that they produce behaviours (and non-behavioural phenotypes) that will reduce their fitness and increase the fitness of other individuals in the population.
As the altruistic behave as to reduce their fitness, they will be at a selective disadvantage and therefore, over time, only selfish individuals will remain.
How can altruism evolve then?
The study of the the evolution (and evolutionary consequences) of behaviour (and non-behavioural phenotypes) that affect the fitness of other individuals in the population is called social evolution. Social evolution is a wide field of knowledge and I will here attempt a very short summary of it so many concepts will be left out!
There are two main (non-exclusive) ways by which altruism can evolve:

Repeated interactions (False altruism)
Kin interactions (True altruism)

Repeated interactions
The concept is grounded within game theory. A good introduction to game theory is definitely out of the scope of this question but I just want to give a little bit of an intuition. I will over-simplified the concepts of game theory but you should definitely have a look at it. Those concepts are very enlightening for questions of evolutionary biology, economy, psychology, sociology and even philosophy.
If for example, the altruistic individuals are actually only altruistic to those
that have shown altruism in the past (via a Tit-for-Tat strategy for example or through the use of reputation), then altruistic individuals may end up have a higher fitness than the selfish individuals. Imagine for example that selfish individuals give nothing and receive nothing. Let's assume that all altruistic individuals, all make one good deed and receive one good deed. Giving a good deed comes at a cost of having, say 0.8 fewer offsprings on average. Receiving a good deed comes at a benefit of 1.2 extra offsprings. Overall and on average, each altruistic individual will produce 0.4 more offsprings than the selfish individuals and therefore, over time the whole population will become altruistic.
We often refer to these concepts as false altruism because altruistic individuals actually has a fitness increase over their life time. Let's now talk about true altruism where altruistic individuals really just give without receiving but yet, the allele coding for altruism thrives.
Kin interactions
Note first that any kin interaction follows within a give game theory scenario. As such kin interaction is just an add-on on what I discussed earlier. For those used to Hamilton's rule, please note that Hamilton's rule apply to Prisoner's dilemna (a type of game theory scenario) only.
So, imagine now that altruistic individuals are being altruistic with their family members (their kins) only (either because they direct their altruism or because there is a strong population structure). Note that such altruistic behaviour can pretty indirect as helping your partner (who we will assume is not part of your close family) will have for consequence that your partner may offer better parental care and therefore by being altruistic to your partner, you are actually being altruistic to you offsprings (which are your kins).
Because the kins of altruistic individuals probably carry the A allele, eve if the altruistic individual is experiencing a lifetime cost in fitness, the A allele may still thrive and the recipients of this altruism are likely also carrying the A allele. In other words, a truly altruistic individual is an individual that sacrifice itself for helping the allele A present in its kins to thrive. In yet other words, true altruism is when an allele is ensuring that copies of itself present in other individual will manage to get passed on.
And this is called Kin Selection. I can now clearly answer your question
Your question

What problem does kin selection solve?

Kin selection explains "true altruism"!
Only "true altruism" can yield to such separation of the reproductive task as that some individuals are perfectly steriles. In your post, you say

From the perspective of the sterile worker: Since it can't reproduce, no strategy will affect the number of offspring it has (will always be 0)

What is missing from this logic is that, 1) at a time workers could still reproduce and 'gave it up' and 2) in many (maybe most?) social species (honeybees, termites, ants and also in non-hymenopteran eusocial species), workers are still able to sometimes reproduce and are also able to overthrow the queen.

Found this: http://rspb.royalsocietypublishing.org/content/282/1803/20142886
"helpers do not necessarily improve their inclusive fitness by foregoing reproduction. These findings suggest the earliest evolutionary steps towards eusociality are most favored if mediated through maternal manipulation.“
That’s what I mean, if this can be achieved my maternal manipulation, then it seems to me to follow, that relatedness isn’t absolutely necessary.
But I’m starting to realize that I asked too broadly and should first read some papers. If I then still don’t get it, I'll post a follow up question.

Kin selection explains a violation of the assumption that individuals will always selfishly promote their own reproduction. (Lemmings jumping into the sea is a myth that does not happen). Every individual is supposed to work toward sending its own genes into the next generation. In your example, you say that the queen should just pump out workers to serve herself. And she does. But the workers are individuals too, with their own genes, and theoretically, should be selfish. However, in this case, due to honeybee reproduction and haplodiploidy, the workers are more than 50% related to their siblings. The math works out such that working toward the success of the colony is a more efficient strategy for promoting worker genes than if the workers were to try to reproduce on their own. Remember that one point in evolutionary time, these workers were reproductively capable, and gave up their own reproduction to serve the colony. So I think that what you are missing is that at some point in time, workers were once capable of reproduction, and gave it up. They were not always cogs in a machine.

"But the workers are individuals too, with their own genes, and theoretically, should be selfish." -> I addressed that: They are sterile, so the cost of their "sacrifice" is 0, which is consistent with selfishness.

"workers were once capable of reproduction, and gave it up." From the little I know, it doesn't like they were the ones who gave it up. It's more like it was taken from them.

They were not always sterile. They evolved from ancestors that were fertile. This is what breaks the rule.

It was not a conscious decision. Kin selection explains the math, and how such behavior could evolve without breaking assumptions about selfish reproduction.

And no, reproduction was not taken from them. Their genes still go forward into the next generation more efficiently than if they were laying their own eggs. It is a kind of decoupling of the individual from reproduction.

Both the worker bee and the queen bee evolved from the same ancestors. Natural selection started to favor individual bees that additionally laid offspring that behaved altruistically.
You say, every individual is supposed to selfishly promote its own reproduction. Yes, but only in accordance to its own power.
If I’m not mistaken, the behavior of a bee is genetically determined. So it’s outside the power of that bee to have more reproduction and the rule isn’t broken (only if you ascribe free will to the worker bee).

Let us continue this discussion in chat.

@KarlKjer Unlike you said "individuals will always selfishly" is NOT an assumption. It is a consequence of NS.

Individuals always acting selfishly to promote their own genes is absolutely an assumption that comes from natural selection, and is violated under the conditions we are talking about. Assumptions are fundamental units of refutation science. Things that are a consequence of a theory are still assumptions.

Well... I disagree with your definition of 'assumption'. If the consequences of all our models were to be called assumptions, then outside of the data themselves, nothing in science would not be an assumption which sounds pretty wrong. I am used to call an assumption, a belief that is not supported by evidences (or at least not necessarily always true in all cases found in nature)  on which a model is based. For example, HWr is based on an assumption of infinite population. However, the allele to genotypes frequencies resulting from the model is not an assumption.


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What would be the Hardy-Weinberg equilibrium condition for a population of haploid organism?
What would be the Hardy-Weinberg equilibrium condition for a population of haploid organism?
Would it always be in Hardy-Weinberg equilibrium?

@Remi.b
campbell biology says that a population of diploid organisms is at hardy weinberg equilibrium only when
p^2 = fraction of population with homozygous dominant organisms
q^2 = fraction of population with homozygous recessive organisms and
2pq = fraction of population with heterozygous organisms
if this relation is not held (between the calculated and observed values) then it can be concluded that the population is evolving
This is how I understood hardy weinberg principle

A) The $p^2$, $2p(1-p)$ and $(1-p)^2$ relationships hold only for bi-allelic loci in diploid populations. It is not a general result. It is obvious that, the frequency of heterozygotes in a haploid population cannot be any different from 0. B) The assumptions of HW equilibrium include absence of selection, absence of migration and infinite population size (hence absence of drift). If a population fits these assumptions, then the population is not evolving, this is true.

What is HW rule?
HW rule is a rule allowing one to compute genotype frequencies from allele frequencies and vice-versa. See Solving Hardy Weinberg problems and eventually Assumptions of Hardy-Weinberg rule for more information.
HWr in haploid organisms
In haploid individuals, the genotype frequencies and the allele (or haplotype) frequencies is the exact same thing! This is because the genotype is a simple haplotype. In other words, once you have the allele frequency, you necessarily have the genotype frequencies without need for any calculation. We can consider the haploid organism would display a special case of HW rule, where there is no assumption and where
$$p = f_{A}$$
$$q = f_{B} = 1 - f_{A}$$
, where $f_{A}$ is the frequency of the genotype carrying the allele A and $p$ is the frequency of the allele A. $f_{B}$ is the frequency of the genotype carrying the allele B and $q$ is the frequency of the allele B.


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What is the need for lobules in (human) testicles?
While I was studying the reproductive system, the question popped up in my mind. Each testicle has lobules formed out of the tunica albuginea, in which there exist seminiferous tubules. Why is the testicle divided in these lobules? What's the point? Why isn't it one single big cavity?

No. Each testicle has lobules formed out of the tunica albuginea, in which there exist seminiferous tubules. My question is why the testicle is divided in these lobules, rather than just being one big cavity. I'll update the question to include this explanation.

The structure of the testes as with many other organs in living things has all to do with form, function, and efficiency. The testes are extremely efficient sperm producers, with on average 1,500 sperm cells being produced per minute in the average human male. If the testes were just an open space of fluid with free-floating sperm producing germ cells, it would not be as nearly an efficient design, not to mention the waste caused by an inability to sort through sperm producing cells and the cells they produced.
According to this site, each lobule in the testes contains about 1-4 seminiferous tubules, each an average of 50 cm in length. Like many structures in the human body, intestinal walls, nephrons in kidneys, etc, the complex structures and organization of the cells that have a specialized function involves increasing access to the inputs and outputs of their function and increased surface area to increase that function.
This site has a helpful graphic showing the structure of the seminiferous tubules that are wrapped up in each lobule. The germ cells which split and create sperm cells are lined along the wall and when the new sperm cell they produce have developed enough, the sperm cell is released to be moved through the tubule where it can be prepared and developed further. This complex structure allows for uniform, controlled, and efficient production of sperm, essentially, a sperm factory running with an assembly line, and is a design that nature has kept and improved upon for millions of years.

Thank you for your answer. However, most of it is offtopic and doesn't really answer what I was asking. Can you back the idea that lobules make for a more efficient design? I can't find anything on the internet.


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Potato Power. Self sustaining medium using a living potato plant possible?
The second picture are potatoes wired in parallel. I understand that the potato is the medium for a chemical reaction between the copper and zinc.
That aside, would wire and in soil potato plant continue to grow replenishing the medium(nutrients and water) regardless of having a current in the potato?
Or
Will the plant react to the physical damage or be depleted of nutrients/water needed to weakening the current or plant?
Maybe the current can be intermittent to allow the plant to recover?
Can the current be low enough not inhibit plant growth?
I would ask chemistry if I was interested how a potato clock works, but I am more interested in the plant health and connections.

I have seen many potato experiments online but none where the potato plant was intact in the soil producing power.

I don't understand why you think the battery's energy comes from the potato. The potato is just a medium for transport of one electrode's atoms (ions actually) to the other.

So you have questions about the ionic conductivity of dirt? I think you need to clarify what your question really is.

Yes, the potato clock will work when still in the ground, but it won't work any better than a potato removed from the ground.
Potato batteries are awesome and cool projects, but they often convey the wrong concept. The energy produced from a potato battery is not from the substance, nutrients, or sugars of the potato, but rather via the galvanic action of the two metals inserted into the potato.
The simple counter to this mental model is to point out that you can make a battery out of salt water, which clearly doesn't have any organic, energetic molecules in it. However, I'll talk a bit more about what's actually causing this effect and why it doesn't work in the way you imagine it might.

The above image is an example of a "potato battery" made without the potato. Identical setup and the energy obtained is identical given everything else the same.
Potato power- er, metal power?
This experiment is supposed to demonstrate the concept of an electrochemical cell. Electrochemical cells obtain their energy from the reduction-oxidation reactions that happen between two metals with different reduction potentials. When two metals - such as copper and zinc - are placed in a medium that permits the exchange of electrons and ions, an electrical gradient is produced as electrons move from one metal to the other and ions move the other direction. This gradient can then be captured and used to do work such as powering a lightbulb or an AI.
In the potato powered example, the power comes from zinc and copper. If you want a more powerful battery, use more zinc and more copper- not a bigger potato. If that is not good enough, try replacing the zinc with something like lithium- this is what we've done with modern, rechargeable batteries.
In truth, the potato battery would be better described as a normal battery that just happens to be inserted into a potato. You'll make a better battery if you use copper pennies and aluminum foil in vinegar.
I do not mean to shoot down your idea, and I am glad you are looking into renewable energy sources- but you may be better served by a class on electricity and batteries than by asking questions on biology.SE!
EDIT: I would assume that the electrical potential of this kind would also kill the plant, given that you're essentially electrocuting it. However, I was unable to find any information on the resistance of potato plants to electrocution.

@Muze I think you're still misunderstanding what happens here. The only thing doing the work is the strips of metal, which aren't alive. The potato could be alive, dead, or something in between- it's irrelevant to the chemistry. Batteries eventually stop working because the electrical potential is "used up", not because they run out of nutrients or life force. Your live potato battery would likewise need to be serviced, with new metals inserted regularly.

I'll direct you to this website: https://www.thenakedscientists.com/articles/questions/can-you-electrocute-plants and this article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2141166/ both of which may provide information for you

While that edit does indeed clarify the essence of your question, it’s not the medium that needs to be sustained to keep the battery functional. It’s the electrochemical gradient created by the metals that needs to be sustained, and that’s independent of the medium.

your answer is very good I don't know why I asked a dup. if you edit it. I'll up vote it

Placing copper on one side of the potato and zinc on the other will not "suck the energy out of the potato".
the energy in the potato NEVER gets converted into electricity. The metals do all the work, just using the potato as a wet sponge.
Now, it would probably kill the potato though, because of all the ions that are there that shouldn't be there (zn and cu), the ~1 volt current screwing up the electrochemical gradients, etc.
So, yes, it would probably die, but not because anything gets stolen from the potato and it starves. Just because the voltage would interfere with cell functions.
The only real way to know is to experiment on a living plant though

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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Is resource partitioning a type of character displacement?
Question
Imagine two related species. They prey on the same species but avoid competition by feeding at different times of the day. Is this a type of character displacement?
Thought
On one hand I have the  Galapagos Finch example, which is typically used to illustrate character displacement. But since resource partitioning is more behavioral than anatomical, is resource partitioning a subset of character displacement or a rough overlap or none?

Welcome to Biology.SE. Is this a homework question? What are you thoughts on the question? My answer is ready, however we have a policy of not answer homework question (or homework-like question) without the OP showing an attempt at answering his/her own question. So I'm just waiting for you to explain your thought process. You can click on edit, to edit your post and add this info

Edited. It is no homework. Just a question that sprouted in my head

@Bakshi please provide evidence that you tried answering this question yourself to avoid having the question closed. Thanks!

Does it look like character displacement?
By the fact that these two species feed at different moment of the day, they therefore have slightly different ecological niches. It is indeed the type of consequences brought about by character displacement. Yes, it looks like character displacement.
"Resource partitioning" is not necessarily more behavioural than anatomical and even if it was, a behaviour is a phenotype, just like any other phenotype, and it should not be disregarded. The character being displaced in a 'character displacement' scenario can be behavioural. So, yes if two species evolve to prey at different time of the day to avoid competition, then they have evolved so as to reduce the overlap between their ecological niche and we can call that character displacement.
Is it character displacement (highlight on a few missing information)?
It is possible (likely) that they evolved to feed at different times as a reaction of their competition and hence it would be called "character displacement" but technically speaking the question does not explain how these two species had been diverging in their feeding. It is possible that divergence in their feeding time happened long before being found in sympatry. In fact, the question does not even make clear that the two species are found in sympatry.