How do you tell one species of turtle from another?

Curiously I find I am moving away from a strict infertility definition to one of functional non-breeding, especially where behavior (bird song) or timing (morning vs evening) or breeding location (return to different locations) isolates members of one group from the other reproductively.Certainly we see things like lama and camel hybrids being possible, so they are not reproductively isolated, it is just rather impractical to consider that they would find a way to interbreed.Functional isolation -- whatever causes the loss of gene flow -- is all you need for independent natural selection of different mutations to occur and cause differentiation between populations; the groups that don't interbreed won't care whether they are or are not interfertile."Species" is a human contrived artificial concept, so if the definition is not as useful in one situation as in another, then we should review the definition.Enjoy

Is there a selection benefit to infertility?Is there a reason\cause that would always end in infertility over generations of isolation?Does infertility play a role in mate selection? Species mate recognition?If the answers to these questions are no, then perhaps we need to look at the definition rather than try to force it in all situations.Sure if two populations cannot interbreed we can be sure they are different species, but if two populations consistently fail to mate due to mate preferences doesn't that result in the same gene isolation?If infertility only occurs through random mutations that are selected for other purposes and not to cause infertility between groups, then actual infertility is a random process, while mate selection preferences are a consistent selection process, ongoing in every generation.So I would say that lack of gene flow is sufficient to define species as a separately, independently evolving group -- which is what is the critical point for macroevolution to proceed.Birds are a great example of how mate selection can cause gene isolation via behavior (mental incompatibility) versus physical incompatibility, but we also have lions and tigers and other examples that have been classically defined as different species even though it is possible to interbreed them.There are also cases of cryptic species that appear similar but don't interbreed. The mosquito that carries malaria has a cryptic sister species that doesn't. They look alike but one population breeds in the morning and the other breeds in the evening, and thereby became genetically separate.Now we could nitpick and say that behavioral isolation just means we have an incipient species and that they aren't fully a new species until we have infertility; but we can also say that we have speciation for all intents and purposes, as the result is the same as far as evolution is concerned.EnjoyEdited by RAZD, : ..