Understanding the Genetics of Speciation

Hi zedman963, and welcome to the fray. Speciation is defined as the reproductive separation of daughter populations, where both descend from a parent population. Unfortunately, that is not the definition used in biological evolution science - all that is necessary in biological evolution science is that the daughter populations fail to interbreed when provided the opportunity. The reasons for the failure could be genetic, or they could be behavioral - the daughter populations no longer see the other population as potential mates, and so do not engage in mating.There are many instances where this occurs, ring species being the most definitive in this regard.See Greenish warblers

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Greenish warblers (Phylloscopus trochiloides) inhabit forests across much of northern and central Asia. In central Siberia, two distinct forms of greenish warbler coexist without interbreeding, and therefore these forms can be considered distinct species. The two forms are connected by a long chain of populations encircling the Tibetan Plateau to the south, and traits change gradually through this ring of populations. There is no place where there is an obvious species boundary along the southern side of the ring. Hence the two distinct 'species' in Siberia are apparently connected by gene flow. By studying geographic variation in the ring of populations, we can study how speciation has occurred. This unusual situation has been termed a 'circular overlap' or 'ring species'. There are very few known examples of ring species.

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There is a change in plummage and a change in mating songs, and both changes occur gradually around the ring until the point of overlap, where the difference is great enough that mating behavior is not engage in between the populations. Close.They also get different random mutations, adding new variation to each gene pool and part of the total set of variations that are subject to natural and sexual selections. The end result is that there are two gene pools with different sets of variations, some are shared and some are not. If the shared genes are involved in mating and mating behavior, then the populations will likely interbreed if given the opportunity. If the non-shared genes are involved in mating and mating behavior, then the populations will likely not interbreed when given the opportunity. Notice that the chromosome numbers are different for horses and mules, just as they are different for humans and chimpanzees, and that this shows substantial changes to the behavior of the genes during reproduction, and thus affecting mating. Peppered moths are a good example of natural selection, however there is no evidence of reproductive isolation between the melanistic and non melanistic varieties. They are evidence of the variation possible within a gene pool, and the selection of those variations under different ecological conditions. Because all the changes that add up to speciation don't occur in one individual, rather it is an accumulation, a cascade, of many mutations that end up different enough to prevent reproduction.Look again at the Asian Greenish warblers - there are 5 varieties in the ring, each breeding with its neighbor variety, each variety being an accumulated pool of differences one from the other, but the two at the end of the ring are separated by four steps between the varieties of pools of different genetic variations - they have accumulated four times as much difference as there is between any of the other neighboring varieties. I suggest you study some courses, texts, whatever is at hand, material on evolution. A good place to start is:Evolution 101 - Understanding Evolution

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What is evolution and how does it work? Evolution 101 provides the nuts-and-bolts on the patterns and mechanisms of evolution. You can explore the following sections:

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It is easy reading and high school to university level material (depending on your schools)Enjoy.

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Hi again, zedman963. But once two populations are reproductively isolated there is no restriction on the gradual modification through mutation and selection of traits that enhance the ability of individual members of each population to survive and breed.In one population of mosquitos, one population bred during the morning and one during the evening, and this behavior difference led to reproductive isolation even though both populations occupied the same ecology and otherwise interacted as one population. They looked and behaved as one species, however it was found that one carried malaria and the other didn't: when looked at in the microscope it was discovered that the shape of the genitals had altered to such an extent that interbreeding was no longer possible and speciation had occurred.When you look again at the Asia Greenish Warblers, there is another think to note: the hybrid zones are small in comparison to each of the habitat zones for the five varieties - implying that the hybrids as less successful in the variety zones competing with "purebred" varieties, and can only exist in the areas where there is sufficient overlap to keep producing hybrids. If these hybrids continue to have less viability and the zones continue to shrink, then a point will be reached where isolation occurs and speciation results.My personal opinion (and I could be wrong) is that behavior changes occur first, resulting in preferential isolation, and that once that occurs, then the genetic changes that result in various levels of sterility and low viability will accumulate.I also don't think that genetic incompatibility is important once behavior has caused the split, because once isolated, genetic changes in different directions to suit different ecologies is an open opportunity for both species to adapt to new and different ecologies. They can acquire different traits not related to breeding, and thus result in added diversity and adaptation to more opportunities.The camel and the llama are adapted to entirely different ecosystems, separated by oceans for eons, and yet they can be artificially inseminated and develop a viable offspring. That doesn't mean that one will survive in the other habitat as well as the adapted species. Genetic incompatibility doesn't need to occur to develop different organisms adapted to different ecologies.Enjoy.Edited by RAZD, : .Edited by RAZD, : ..

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Thanks Wounded King, perhaps I overstated it. Correct, but what we have are living individual camas, a rather incredible seeming thing when we realize that they have been isolated populations for multimillion years with no chance of gene flow through intermediate species or forms, separated by an ocean as well as time.What this shows is that the mutations and selections involved in the evolution of camels and llamas did not have to cause a prevention of the ability to interbreed for them to be better fit to their respective ecologies. But it is, perhaps, an extreme example of a lot of evolution and adaptation, by two daughter populations over an extended period of time without necessarily destroying the ability to interbreed in the process, and it demonstrates that the standard of necessary genetic incompatibility is much higher than is necessary to explain the diversity of life as we know it on the planet.Thanks.

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Hi again zedman963 Yeah. At this point well just say "able to produce some living individuals with artificial breeding" and that this shows that total genetic incompatibility is not a necessary criteria for speciation. So what happened in the camel and llama populations while they were separated?Don't think of it as a single step. I can walk from Rhode Island to California, but I can't do it in one step, nor can I do it in one day: it takes many steps spread out over many days.Each population can - and does - allow variations in the genes such that individuals each have essentially unique combinations within a population. New variations are added by mutations and old variations are eliminated by selection or by genetic drift, and the makeup of variations in the populations changes over time, generation by generation. With these generations individuals reproduce, some are infertile or miscarriages, including ones with old genes, and some are viable and robust, including ones with new genes.Individuals only need to be able to reproduce in their generation, not with their ancestors, nor with their descendants, and a little change with each generation can add up to major change in many generations (though it does not have to, there is just the opportunity for it to do so, an opportunity that does not exist within a single population in a single generation).Enjoy.

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