DNA and identifying species has been a lot in the news lately. I found an interesting bit of science here on Deep Sea News about using DNA to identify cryptic species. Cryptic species are not related (not directly, anyway) to "cryptids" or cryptozoology. Cryptic species are those which are very, sometimes impossibly, difficult to distinguish from related species. Birders may grouse (get it?) about all the "little brown jobs," but the situation gets a lot worse when you get to the invertebrates.
As Dr. Holly Bik explains, "A species is a hypothesis." She then writes, "But that doesn’t mean DNA is a magic bullet. DNA provides a new type of evidence for making decisions about species, but that evidence still has to be robustly analyzed and interpreted in the context of historical knowledge (taxonomic classifications and anatomical features of specimens)." Her example here is a genus of sea slugs everyone had thought were pretty well described. Scientists applied "four independent methods of molecular based species delineation" and found that they no longer had two species in the genus: they had 12. There's a good overview here of the process used.
Dr. Bik concludes that the whole species thing is still devilishly hard to sort out (and remember, the species is the most well defined of traditional taxonomic units). It's no wonder people like Dr. Darren Naish advocate giving up on the Linnaen classification system altogether.
Bik closes: "Next time you hear a “global species estimate”, don’t say you believe it, please don’t say you believe it!"
Generally, the End Pleistocene giant mammals are considered different species from their current, smaller analogues, mostly due to this one difference. Sometimes they are still thought to be the same species. The giant cheetah and the current cheetah are supposed to be the same species. The giant North American beaver is considered a different species than the present one. It was up to the size of a bear. However, when the red deer was introduced to New Zealand in the 1800s it's size increased by 50%. The End Pleistocene giant mammals were 30-50% larger than their present analogues. The red deer was larger during the Pleistocene. This makes them chronospecies.
ReplyDeleteChronospecies gets into conflicting models of speciation and classification - it's a very interesting concept, but not one I want to try to puzzle out ! It's been argued the North American cheetahs were not cheetahs at all. This gets very complex very quickly.
ReplyDeleteDo you know, are North American cheetahs very different from Old World Pleistocene cheetahs? My suggestion was along the lines that the concept of chronospecies simplifies the classification system as there are obviously fewer chronospecies than species.
ReplyDeleteThe relationsips are debated, but the American Miracinonyx (there were two or three species, depending who you cite) seems more to be about convergent evolution (same niche, similar conditions) than actual relationship to the African cheetah. It was fascinating to speculate the onz might have been a surviving Miracinonyx, but the DNA established it was just a weird puma.
ReplyDeleteI know. That was what hooked me into studying about the onza. Can you say whether the Miracinonyx was more like an African cheetah than a puma?
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