Taxacom: replacing un-sequenceable types (was Re: Minimalist revision of Mesochorus)

[Richard Pyle]

Hi Marko,

> Why do I think that that only-DNA would be the best approach? In short,
> because species delimitation is largely bound to be arbitrary. 

I wholeheartedly agree!  And because of that, I think it's in the best interest to all of taxonomy to maintain a more-or-less consistent "calibration" for where we should draw these mostly arbitrary lines between species.  In other words, just because modern tools for DNA sequencing afford us the ability to recognize consistent patterns of variation/lineages among populations and greater resolution/granularity than more morphological/traditional/historical approaches, we probably should not have that result in ever finer resolution/granularity in what re recognize as distinct "species".  I worry, because I do see a trend towards more aggressive "splitting" just because there are consistent patterns appearing from DNA sequences.

Aloha,
Rich

> For example,
> probably most species' distribution is patchy, with isolated populations being
> differentiated to the various degrees. With my colleagues, I have written about
> this allopatry problem in species delimitation in several articles. Because
> speciation is a gradual process, delimitation of diverging populations is
> inherently arbitrary. 

Again, agreed!

> As so, the best would be to base it all on quantifiable data,
> i.e. DNA. That would serve the stability the best as enabling standardization.

Mmmm.... not so sure I agree.  There is a lot of "physics envy" in taxonomy; but just because an approach relies more on quantifiable data, doesn't make it more useful.  We imagine boundaries between groups of organisms as discrete entities, and then reinforce those boundaries by assigning labels (scientific names) to those mostly-arbitrarily defined clusters -- and the reason we do that is to facilitate communication among biologists, such that a scientific name, which is a proxy for the name-bearing type, which is a proxy for some set of living, recently dead, and yet-to-be-born organisms we assert to represent a "species", has proven to be a useful means of communication for more than two and a half centuries.  Whenever I see someone say "a species is a hypothesis", I actually agree but not in the way it is usually intended.  The testable hypothesis of a "species" is in the field of sociology and linguistics; along the lines of "Humans will achieve more effectibe and efficient communication by regarding these two sets of organisms as distinct species, rather than as a single species".  In other words, the hypothesis has nothing to do with taxonomy or evolution or whatnot.

> Also, finally all taxonomically relevant data is encoded in DNA, as you also
> stated. Be it ecological, morphological or whatever. Even when we do not know
> yet where this information is hidden in the genome, it is still there.

I've been making this point for literally decades (plural).  However, I also qualify it with "but we're nowhere near close to understanding genomic information to use it in place of more traditional means of determining species boundaries".  I agree we're getting better and better at it all the time, but I still don't think we're even close yet.

> I am also convinced, given the unprecedented progress of genomics
> technologies, that not far in the future recovering entire genomes of organisms
> is both straightforward and cheap. Once we can retrieve huge amounts of
> information (and all that matters) in such an easy way, why shouldn't we take a
> full benefit of it?

Again, I fully agree!  But just because we have (or will have) the ability to extract full genomes cheaply, doesn't mean we automatically understand how to synthesize that information in such a way that it yields proposed species boundaries in a way that is more or less consistent with how things have been done for the past 250+ years.  Sure, we could take advantage of the new technology to refine what we mean by "species"; but why bother?  The lasting value of "species" as an entity is to allow some degree of consistency in communication across decades or centuries.  If we're going to break that (i.e., if we decide to fundamentally recalibrate the granularity of sets of organism we apply that term to), wouldn't it be better to just come up with a new word and methodology so as not to disrupt the historical continuity of what a "species" (more or less) has meant?

Aloha,
Rich


Richard L. Pyle, PhD
Senior Curator of Ichthyology | Director of XCoRE
Bernice Pauahi Bishop Museum
1525 Bernice Street, Honolulu, HI 96817-2704
Office: (808) 848-4115;  Fax: (808) 847-8252
eMail: deepreef at bishopmuseum.org
BishopMuseum.org
Our Mission: Bishop Museum inspires our community and visitors through the exploration and celebration of the extraordinary history, culture, and environment of Hawaiʻi and the Pacific.