Do we need to describe every cryptic species? What do we do with old names? Can we make this more simple?
By Joe Zuccarello, Victoria University of Wellington
Describing species, mostly nowadays on molecular data, is coming into conflict with the rules there are established to give guidelines and provide stability in naming species (e.g., type specimens, name priority…).
Defining and recognizing species has led to lots of ‘problems’ in the past, but almost everyone interested in biology realizes that being able to recognize species is important for any further work. You can’t contrast the physiology of two organisms until you know you have different, or the same, species. Sometimes it is trivial, everyone would know that Sargassum and Alexandrium are not the same, but if you want to study toxicity in dinoflagellates it may be important to know which Alexandrium species you have; if you are interested in gene flow between populations, it may be important to recognize the same species of Sargassum. And of course, a correct taxonomy is needed to study the processes that produced that diversity.
So how do you identify species. In the past, this was done almost solely by morphology. This is very useful, but in algae can also be problematic. You need some training to count dinoflagellate plates, and Sargassum is notoriously phenotypically plastic, so morphology may not be easy to implement.
We are stuck with nomenclatural rules (laws even), and linnean binomials, that must be followed to recognize a species as new. This includes making sure no one described it before (i.e. an older name) and applying the name to samples that you think are the same as the type specimen (the first description of that species).
Maximum likelihood (ML) analysis of a phylogenetic reconstruction of Bostrychia samples. Reproduced with permission. J. Zuccarello
Two issues I want to discuss are cryptic species and pre-existing names. Cryptic species are organisms that are distinct genetically, to the point that you would like to consider them different species but are indistinguishable morphologically. This is becoming the norm in algal studies. Nearly all previously widely dispersed species turn out to be composed of different genetic clusters (often with more limited distributions). Even if you think they are multiple species, or have other evidence for species status (reproductive isolation), should you name all (a novel binomial for often many) these cryptic species?
But now you have to determine which of the cryptic species should have the original name, which should get new names, and which may have already been named, and in the past merged into the oldest name (synonymized) and therefore you need to resurrect the names. That is the rule (the law!), the name, if validly described, is an older name that will have precedence over any new name you may like to give. But how can you figure it out as this alga looks the same as the ones dead on an old sheet of paper?
I think you need to be bold, and willing to be contradicted, and just go ahead. If the type specimen is from Europe (collected there) and most of the samples of one of the ‘morphologically identical’ species is collected in Europe, then use that name! Same goes for the other older names, samples mostly from Japan and an old synonymized name from Japan... What if all of the cryptic species are cosmopolitan (sympatric almost everywhere), and you can’t get DNA data from the type specimen (obviously not always possible). You can either throw up your hands and curse the nomenclatural committee or be arbitrary and assign. This must be a way forward.
With the continued evidence of many ‘cryptic species’ based on molecular markers, and a ‘slightly’ archaic nomenclatural system based on specimens that are old, or just drawings, or lost, we are reaching a point when the laws that were supposed to aid taxonomists, and give some stability to names, are really becoming a hindrance. If we think taxonomy and sticking to linnean binomials is still relevant, then we need to move on.