The level of genetic variation of human immunodeficiency virus type 1 (HIV-1), a member of the lentivirus genus of the Retroviridae family, is high relative to that of retroviruses in some other genera. The high error rates of purified HIV-1 reverse transcriptase in cell-free systems suggest an explanation for this high genetic variation. To test whether the in vivo rate of mutation during reverse transcription of HIV-1 is as high as predicted by cell-free studies, and therefore higher than that rates of mutation of retroviruses in other genera, we developed an in vivo assay for detecting forward mutations in HIV-1, using the lacZ alpha peptide gene as a reporter for mutations. This system allows the rates and types of mutations that occur during a single cycle of replication to be studied. We found that the forward mutation rate for HIV-1 was 3.4 x 10(-5) mutations per bp per cycle. Base substitution mutations predominated; G-to-A transition mutations were the most common base substitution. The in vivo mutation rates for HIV-1 are three and seven times higher than those previously reported for two other retroviruses, spleen necrosis virus and bovine leukemia virus, respectively. In contrast, our calculated in vivo mutation rate for HIV-1 is about 20-fold lower than the error rate of purified HIV-1 reverse transcriptase, with the same target sequence. This finding indicates that HIV-1 reverse transcription in vivo is not as error prone as predicted from the fidelity of purified reverse transcriptase in cell-free studies. Our data suggest that the fidelity of purified HIV-1 reverse transcriptase may not accurately reflect the level of genetic variation in a natural infection.
"Beneficial" vs. "neutral" vs. "negative" are relative. A "neutral" mutation can turn out to be "beneficial" if a certain environmental pressure selects for it (or negative if an environmental pressure selects against it), but absent that environmental pressure, the mutation essentially does nothing meaningful. These are all subjective words defined by humanity - mutations themselves simply are, and do occur at a statistically predictable rate.
Take, for instance, an imaginary mutation in a bacterium that makes it resistant to a certain antibiotic, but more vulnerable to another type. In the absence of both antibiotics, it's a neutral mutation. One antibiotic or the other could make it a positive mutation or a negative one - it all depends on the environment. We can predict how often mutations will occur, but there are additional variables for "positive" vs "negative" vs "neutral," and they can even change during the lifetime of the organism. So your question is meaningless.
Edited by Rahvin, : spellign.
When you know you're going to wake up in three days, dying is not a sacrifice. It's a painful inconvenience.
As I pointed out to Faith there is no evidence that there is a problem. Faith simply assumed that the rate of loss must exceed the rate of gain (without giving reasons). However there are theoretical reasons to doubt that (the rate of loss must decrease as the number of alleles decreases, and a dynamic equilibrium is the most likely position). Few wild species show a seriously depleted gene pool. Considering all changes at the genetic level neutral drift dominates over selection.
And tying into speciation, the most rapid evolutionary change occurs when selection is relaxed. Small isolated populations are thought to be the usual source of new species not because of selection pressure but because genetic drift has a greater effect in small populations (and founder effects are relevant, too). This doesn't suggest that speciation has a particular problem with losing alleles through selection.
Let me add that these points do not mean that selection is unimportant. It is very important, but its impact on genetic diversity is not so high as you seem to think.
Domestic selection, involves intense selective pressure - while almost certainly relaxing pressures the wild population would be under. Taking domestic selection as a model without considering how it differs from natural selection in the wild is bound to be misleading, quantitatively and qualitatively.
Now I don't know if there are any studies out there addressing precisely the point you want to look at. I don't even know if it would even be practical to produce one. It's up to you to explain what you want and then maybe we'll know.
Presumably, the evo study substantiating this most basic claim would give it's reasons.
I haven't got a clue what you are asking for, hence why I asked for more detail.
Just show where a peer-review study has been done, or perhaps there hasn't been any?
If it is so important, it is basic, and it undermines evolution, I'm sure an IDer has done the work necessary.
Just evos asserting something with no real published science to back it up
I'm not asserting anything, rand. I spoke of a possible outcome regarding diversity and you started making demands about beneficial mutations. If you want me to show studies about increasing diversity by allowing a population to grow after a bottleneck - that'd be relevant.
This is a very interesting fact on it's own. Can you speculate more on why they can interbreed despite being less related to jaguars and leopards, or maybe they can interbreed with leopards and jaguars too, but no one has tried to do that....maybe they would fight too much or something?
I think you may have get the relatedness a bit wrong, but I'm not sure if you did, so I'll restate, just in case. Lions are more closely related with leopards, then with jaguars I think, and only then with tigers. Nevertheless, hybridization is more successful with lions and tigers, more specifically, with lions and tigresses, and not so much with tigers and lionesses.
It's reported that lions can indeed generate hybrids with leopards (and perhaps with jaguars), but it's just far more rare by some reasons, first of all, species tend to mate with members their own species, obviously, so it would hinder natural occurrences*. Secondly, in captivity, they'd presumably be more often kept separated than lions and tigers due to the larger size difference, so leopards would be safer and under less stress. Thirdly, and perhaps the more meaningful here, possibly there are more relevant differences in the embryological development of leopards and lions than there are between lions and tigers, of similar size.
To illustrate, I'll briefly explain why hybrids between lions and tigresses are more viable than the hybrids of tigers and lionesses: in the production of the gametes, there is one process called methylation, in which the expression of certain genes is hindered by a "chemical lock". Males and females will sometimes "compete" with each other using these chemical locks. Males can have more multiple sexual partners than females, often at a considerably lower cost (as the females are the ones who get pregnant and often do most of the nurturing of the offspring). They can have fitter offspring if they could have gametes that would instruct the growing embryo to develop as much as possible, to suck up the resources of the mother as much as it does not backfires (she must be healthy enough to giver birth to the offspring and nurture it effectively). It is actually done by the males with these "chemical locks" on the gametes.
For females, in the other hand, they would benefit if they have gametes that would counter act that, instructing the embryo to take easier on her, so they could recover more easily and have better chances to eventually have more offspring with another mate, or at least be healthy enough to nurture better the current offspring itself.
When a males have access to multiple females, and the females are related and social, as in the lion's pride, the strategy can be driven to an extreme. The lion's gametes will instruct the development to exploit the female to the maximum, as the threshold of viability is stretched; the bodily resources of each female can be more exploited. Even if a female is exhausted and weak after giving birth, her sisters, older and younger ones, which hadn't gave birth exactly at the same time, will help taking care of the young.
With tigers, that does not happen. So the sperm does not instruct the "cheat" the embryo to grow the most. The ovum also does not counter act this "cheating", so the offspring will be a healthy tiger cub. But if a tiger sperm fecundates the egg of a lioness, then the embryo has no much emphasis on growth from the sperm, and many growth restrictions imposed from the lioness' egg. Then the result will be a weak "tigon" cub, which if survives the whole development and reaches adulthood (which is rare; apparently they often die on the development itself or short after birth), will have a smaller body size and shorter lifespan. In the other hand, when you get the sperm of a lion, with plenty of instructions to develop as much as possible, and the egg of a tigress, without the counter measures for such exploitation, if the pregnancy is successful (not as uncommon with tigons, I think), she will giver birth to a "liger", which, if reaches adulthood, will be bigger than both parents (the biggest cats alive today are ligers, even though some are overfeed in order to exaggerate their weight), and may even live longer, I think.
A similar process may restrict even more drastically the success of hybrids between lions and leopards, but perhaps driven by "real" genetic differences (not just epigenetic/methylation). The gametes of each species may have growth instructions that don't fit conjointly, and also perhaps there is different gestation times for each species which would only make the whole thing even messier. But perhaps would not be so troublesome with tigers and leopards or jaguars, but I don't know of any case of hybrids between these, while there are at least one allegedly case of hybrid between lions and leopards.
One could test the idea by impregnating them under medication....but cruel, but still, it would be interesting to see?
I don't quite get which medication you have in mind. Anyway, perhaps it's not done because scientists actually know better what's going on and don't have anything interesting to learn from that. And perhaps a similar principle could be tested with, say, mice and rats, or some fish species, something more suited to the lab, with less ethical implications due to the rarity of the species and all these things.
* Not so much as the natural occurrence of lion-tiger hybrids is hindered, as they almost never coexist in the same habitat, lions are mainly african, and tigers are mainly asian. They do met in India, even though I think that lions still inhabit savannas there while tigers live in the jungle. But species are probably rare there, if not extinct already anyway)
Let's just see the studies showing higher beneficial mutation rates exceeding the rates of genetic decrease through isolation.
That's not a requirement at all, for either NS or speciation by NS (including AS).
An important point that I don't know if has been made already: there are different concepts of species, implying in different requirements for each sort of speciation.
There are species (eco-species) that differ adaptively but can can fully interbreed (such as finch species of the genus Geospiza), and these are more less analogous to dog breeds and probably less important to the whole thing, as are generally more accepted by creationists, which would only say that it's enough. It's mostly this that is driven by NS, adaptive differences, not reproductive isolation. Unless strong, reproductive isolation by hybrid inability is itself highly adaptive in some times, which I'm not aware of.
I think that most of the time the would-be "hybrids" (the ones on the forming "adaptive valley") will just be selected against when a species is splitting by NS, and there would be just too many individuals of the same recently-split population to mate with each other, keeping the adaptation, that eventual mutants with the beginnings of an adaptation for selective infertility wouldn't have enough advantage with that.
Perhaps even a tremendous disadvantage, as it could also result in speciation from its own eco-species, which is bad in two ways: diminishes the size of the total population (as it wouldn't not be able to mate with the original new eco-species, only with a few new members of the brand new bio-species), at the same time that it will have to compete with a more populous species (the species it came from) for the same niche, likely in the same habitat. Unless this bio-speciation happened to occur conjointly with some huge advantage, it's far more likely that the recently split bio-species will go extinct, and there will be only eco-species.
Furthermore, the isolation between the eco-species can be achieved behaviorally, by "imprint" of the phenotypical traits of its own species; that is, the individuals "learn" with whom they're supposed to mate. That happens even with some spiders. That would avoid the cost of eventual unfit hybrids, but the species would be still able to produce fertile hybrids for a long time (perhaps almost indefinitely, if the situation hypothetically remains the same indefinitely).
More "real" bio-speciation will happen in basically two ways: after a long accumulation of adaptive differences, gradually hindering the viability (and fertility) of hybrids, that's the "adaptionist/selectionist"* pathway; or, by the accumulations of a certain key-mutations that are not really adaptively important, but just happen to hinder the viability of hybrids ("neutralist-mutationist"* pathway), which would presumably, eventually be followed by divergence by natural selection, either by differences for each habitat, or selection for character displacement, if the two related species eventually met again in the same habitat. The former I think was proposed mostly by Ernst Mayr, and the latter by George Romanes, a less known contemporary of Charles Darwin. It can also be somewhat mixed; the key-mutations that cause speciation being related with adaptations for different niches.
The latter is pretty hard to be "induced" by NS, it is totally accidental. The former, perhaps already happened to some degree with dog breeds. Would the hybrids of a great dane and a chihuahua by viable? I don't know, but I wouldn't be surprised if not. Perhaps scientists could breed some strains of some thing for speciation, for some reason, if that's really interesting. Other line of research would be to compare closely related species and with actually makes induces the biological barrier to hybridization. Then, if it's a heritable and variable trait, it's eventually changeable by natural or artificial selection.
It may be interesting to mention that there's a bacteria, Wolbachia, which causes a sort of speciation on its hosts. I think that Robertsonian translocation also has already been witnessed in other species (some rodent, I think) in a way that may be satisfactory to many creationists also.
* - I'm almost making up these composed terms. Perhaps just one of each is more adequate/enough, or maybe another terms entirely. But I think anyone gets the idea.
The latter is pretty hard to be "induced" by NS, it is totally accidental. The former, perhaps already happened to some degree with dog breeds. Would the hybrids of a great dane and a chihuahua by viable? I don't know, but I wouldn't be surprised if not.
IIRC, there's a couple of large dog breeds which you must never breed together, because one of them is large by virtue of producing more growth hormone, and the other by virtue of being more sensitive to growth hormone, producing a developmental disaster when you put the genes together.
I'm sorry I can't remember more, give references, et cetera ... does anyone else know more about this?