[Taxacom] FW: DNA only descriptions

[Doug Yanega]

To follow up on Sergio and Thomas' comments:

Kim van der Linde wrote:

>Well, DNA barcoding is exactly developed for doing just that, with the
>added advantage that you do not need to know all your species.
>
>For insects, we only need one leg (even from a living individual) to
>make an ID, without even knowing what family those individuals are in.

If you are talking about using multiple genes, including ribosomal 
and/or nuclear, then this might be true. If you are talking strictly 
about COI barcodes, then it is demonstrably not true. It is known 
that a single species can have more than one COI barcode, and that 
multiple species can have identical COI barcodes. In some cases, 
there are extra copies of the COI gene elsewhere in the cell, meaning 
the same *individual* can yield more than one barcode. In practice, 
COI sequences do not *always* map one-to-one with species boundaries, 
therefore the claims about accuracy of ID are overinflated (and 
under-tested; how many putative cryptic COI-based species have been 
subjected to attempts to interbreed, to confirm their reproductive 
isolation?). We might not be having this discussion if the gene 
selected as the "default option" for barcoding had not - as in COI's 
case - been linked to the mitochondrion, and therefore prone to all 
sorts of non-Mendelian artifacts. Ever hear of Wolbachia? 
Mitochondrial sweeps? Hybrid introgression? For a tool that is used 
so often, by so many, to have so many situations where it can be 
expected to fail, is not very comforting if that's the only tool in 
the proverbial kit.

I do not have any real issue with research that utilizes data from 
multiple genes - I suspect that many of us "naysayers" would admit to 
this - but the barcoding *concept* (that we can get by with a single 
gene for *every* life form on the planet) is not realistic, 
especially in the case of COI, and investing a lot of time and energy 
in that sort of thing to the exclusion of other approaches can 
undermine the function of the systematics community. To return to the 
original point of this thread, it is certainly possible for a taxon 
to be recognizable and diagnosable solely by virtue of its genome, 
and to be named on such a basis - but I would argue VERY strongly 
against it were it to be based on a single gene, especially a 
mitochondrial gene. One piece of evidence does not automatically 
constitute proof.

Sincerely,
-- 

Doug Yanega        Dept. of Entomology         Entomology Research Museum
Univ. of California, Riverside, CA 92521-0314        skype: dyanega
phone: (951) 827-4315 (standard disclaimer: opinions are mine, not UCR's)
              http://cache.ucr.edu/~heraty/yanega.html
   "There are some enterprises in which a careful disorderliness
         is the true method" - Herman Melville, Moby Dick, Chap. 82