How do you tell one species of turtle from another?

The paper gives a discussion of the reasons for the classification by DNA of the turtles as different species. The rationale does not include any consideration of interbreeding. The idea expressed in the article is that the different species have had little to no gene flow between them, and the time of divergence is expressed in millions of years in the past as opposed to being of recent vintage.

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Each of the two taxa have numerous private alleles, implying very little recent gene flow, and they are as genetically divergent from each other as the other named species are from one another [11, 13, 20]. Previous studies have also revealed the existence of a limited amount of introgression between the two taxa [11, 13, 20], which is not unexpected given their geographical proximity.

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I take this sentence to mean that the two taxa can interbreed, but that they have genetic divergence on the order/magnitude that we find between species under the current classification system. Yeah, that seems to be what is going on. I would add though that the kind of genetic separation involved probably would not exist if there were unrestricted interbreeding.Edited by NoNukes, : No reason given.Edited by NoNukes, : No reason given.

Is the lack of sense because you are trying to force fertility into the definition? Perhaps your definition is not flexible enough to capture actual usage of the term.From the wikipedia article on species.

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in biology, a species (abbreviated sp., with the plural form species abbreviated spp.) is one of the basic units of biological classification and a taxonomic rank. A species is often defined as the largest group of organisms where two hybrids are capable of reproducing fertile offspring, typically using sexual reproduction. While in many cases this definition is adequate, the difficulty of defining species is known as the species problem. Differing measures are often used, such as similarity of DNA, morphology, or ecological niche.

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If inter-fertility is not a hard and fast part of the definition, then that would seem to address the question you ask about making sense.

To be completely fair to the article authors, the rationale for saying that the turtles are of different species is given in the article. The rationale given boils down to saying that the genetic differences are greater than the differences between other groupings of turtles which are already designated as different species.The other thing to note is that regardless of the degree of certainty expressed in the article, what is written is the opinion of the authors. My inclination is to agree with their rationale, but the designation of species and sub species is somewhat in the eye of the beholder.ABE:I took a look at the wikipedia classification on birds, not only are there interfertile species of birds, there are bird hybrids formed from pairs of birds that are classified as different genii and different families although the latter is described as rare. Edited by NoNukes, : No reason given.