What is a species? This is a question that every new biology grad student seems to get fixated on at least for a while. Personally I found the book by Jody Hey: “Genes, Categories, and Species: TheEvolutionary and Cognitive Cause of the Species Problem” to be a satisfactory and sufficient exploration of the topic. After reading the book, I came to the conclusion that for me (I am purposefully ignoring viruses and bacteria) species are something which exist in nature, they are groups of organisms that all share an evolutionary trajectory. Because we cannot travel to the future the true boundaries of species are inherently unknowable. Names are something else. To me names are things we give to organisms that allow us to intelligibly discuss relatively discrete groupings of populations.
Unfortunately, no simple scheme for assigning ranks and names to taxa can deal with the reality of biological processes. I think a perfect example of this was a recent paper: “Species designation of the Bruneau Dune tigerbeetle (Cicindela waynei) is supported by phylogenetic analysis of mitochondrial DNA sequence data” Cicindela waynei is a geographically isolated species which was described like most species based on morphological evidence for differences between it and its closest relative the more widespread C. arenicola. This new paper looked to molecular evidence (mitochondrial) to see if it was congruent with the morphological evidence.
The authors of the paper believe their study shows support for the naming of the species and even show some support for the idea that this species may have arisen due to isolation after late Pleistocene flooding events (cool story). I really don’t have any argument with any of this (though nuclear loci would have been nice). The problem is elevating this population to species status does not reflect the fact that in their analysis they did not find reciprocal monophyly.
Reciprocal monophyly is what you would hope to see. It makes for a nice clean picture and a clear decision. If they had found it the phylogeny of all of their populations would have looked like this:
However what they did find was a topology like this:
Here we see the new species is actually nested within the arenicola. To me elevating its taxonomic rank to the same level as arenicola actually reduces the value of the names because they no longer reflect the closeness of the association between the two putative species. My first thought is maybe this is a good example of when subspecies (my least favorite classification) actually makes sense. Perhaps what we are seeing is incomplete lineage sorting or as the authors suggest maybe some of these other populations should also be broken out into separate species. I don’t know what the right answer is but I don’t think this data is necessarily clear support for species status of the Bruneau Dune population.
Despite my issues I did enjoy the paper and its always fun to think about how we should classify populations and the kind of hypothesis that we can really support with our limited information.
Hope everyone has a great holiday!