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May 21, 2018
Michael C Singer
Biological and Marine Sciences
University of Plymouth
I must congratulate you. I read Nature regularly, wistfully wishing for articles that address fundamental issues with the force and clarity of Michael C Singer and Camille parmesan “Lethal trap created by adaptive evolutionary response to an exotic resource” Nature vol. 557 May 10, 2018 page 238. I propose a question, and am hard pressed to analyze it, but I think your work makes you uniquely prepared for it. I shall even propose an answer for you, viz: “Balderdash you silly old coot; speciation takes more than ten generations, probably more like a couple thousand.” But let me prattle on.
Most people, intelligent folks who can put their shoes on in the morning, when asked about inbreeding will respond: It’s caused by bringing together two bad copies of the same gene. That leaves the function of the gene lacking with a bad outcome. First cousins can marry with only a trifling loss of fertility, but it builds up over generations until it is very bad.
Really. That explanation is totally delusional. Recessive deleterious genes will be rare, of course. Any rare gene will be eliminated by genetic drift. During reduction division at meiosis, one gamete will seem to be in trine and the other star crossed. (Yes, that totally screws up astrology, but astrology is screwed up anyway. It’s just a figure of speech.) One may find itself forming a zygote, and if so, then the other just about certainly goes out with the wash. Since in any one generation a gamete and its chromosomes have a fifty-fifty chance of being lost. Starting out with the same prevalence of a gene, it will be cleared from a small population faster than from a large population. This is part of the foundation of population genetics.
It’s worse when you consider deleterious recessives. In a large population any deleterious recessive will take longer to find its counterpart. Here is a link to a more thorough rant. https://www.youtube.com/watch?v=Qk8F2Bme1J8&feature=youtu.be
No matter. We know how to avoid inbreeding. But in fact it cannot be explained on the basis of genes. It has to be epigenetic.
A more poisonous delusion is this: a larger and more diverse population is always better; it provides more material for evolution. But consider. Selection is a race. Therefore speciation is a race. If there is a new niche (begin to feel eerily familiar?) the species that can speciate can hold onto its old niche and also have a daughter species seize the new one has a long term advantage. In fact, where your butterflies divided into a population that optimized for the new kind of food and one that clung to the old, the new form went extinct when the niche closed. But it didn’t have to be that way. Had only the old niche closed, then survival of the line would have still been probable.
Now selection is a race, so speciation is a race. So let’s say speciation takes 2,000 generations. A valley of butterflies is cut by a glacier, which endures 2,000 generations. The glacier melts. But flies from one side cannot have fertile offspring with the other; this is plain old garden variety allopatric speciation. Something about the chromosomes does not match. Now say the population is over 1,000 with random mating. The two most closely related genes bounce around over the generations among a population of 2,000 chromosomes. On average, by the time they get back together they have been separated just as surely and just as long as if the glacier had happened. No fertile offspring. Since this is true of all parts of all chromosomes, the population dies. Extinction of the fittest is not what we expect. So there is strong selective pressure to maintain a population between one and 1,000. (rant goes on longer at https://www.youtube.com/watch?v=sndHooZ5B6M&feature=youtu.be
Or you can go up to the scripts link above and look at number 2.)
Well this has been shown by a team led by Richard Sibly (https://www.youtube.com/watch?v=sYFRe2SqKk4&feature=youtu.be). The pattern is as real as inbreeding depression. Now as it turns out a population of humans will die out in about 10 generations, just as your butterflies did. (https://www.youtube.com/watch?v=IJH_vX3HETE&feature=youtu.be) That is probably a fluke.
Under normal circumstances, had the new niche been extensive and enduring, the butterflies would have moved out and established new sub populations just as black footed ferrets did when released into the wild. (https://www.youtube.com/watch?v=ADbsguVsKQA&feature=youtu.be) This would have kept their populations in the safe range.
Had it been I and I had stumbled across your butterflies I should have simply concluded that they were a new species. So here is my question:
If we call standard speciation genetic speciation, is there such a thing as epigenetic speciation? My shriveled brain can’t sort it out. It seems to me you have been the first ever to observe speciation, be it genetic or epigenetic. Let me know what you think. You might want to plow through the links under the scripts link. Bit of work, but there is a Nobel prize for genetics, and I understand it includes money.
Let me know what you think.