[Taxacom] very nice opinion article in today's Zootaxa

James Whitfield jwhitfie at life.illinois.edu
Fri Sep 16 17:36:06 CDT 2011


Not to argue for using only one sample to stand for a species, or only one
DNA barcode, as I agree with you that it is a bad idea.

But if people would bother to look carefully at the original papers, they
are based on LOTS of molecular samples from each species.  It is the
CONSISTENCY of the molecular or morphological differences that is
critical, not how major the differences are. In this case the molecular
and morphological differences are consistent across many samples within
putative species and do indeed support one another.

Most species descriptions based on morphology (probably 95% + of all
species descriptions?) do not have any convincing analysis associated with
them. We are in the habit of trusting the experts in this case rather than
requiring strong evidence.  Most of the time this works really well, I'd
say.

Jim




> Exactly. The question is whether a one specimen sample will suffice for a
> species description. YES, that the specimen is connected to a systematic
> morphological study of many specimens is importanat, but it is not support
> or refutation of the morphological conclusions. Only if the molecular
> analysis can stand on its own can it either support or refute another
> concept.
>
> _______________________
> Richard H. Zander
> Missouri Botanical Garden
> PO Box 299
> St. Louis, MO 63166 U.S.A.
> richard.zander at mobot.org
>
>
> ________________________________
>
> From: taxacom-bounces at mailman.nhm.ku.edu on behalf of Doug Yanega
> Sent: Thu 9/15/2011 5:05 PM
> To: TAXACOM at MAILMAN.NHM.KU.EDU
> Subject: Re: [Taxacom] very nice opinion article in today's Zootaxa
>
>
>
> Among the references that John Shuey listed, I noted the following
> one, which I had not seen before:
>
>>Burns, J. M., D. H. Janzen, M. Hajibabaei, W. Hallwachs and P. D. N.
>>Hebert 2007. DNA barcodes of closely related (but morphologically
>>and ecologically distinct) species of skipper butterflies
>>(Hesperiidae) can differ by only one to three nucleotides. Journal
>>of the Lepidopterists' Society, 61:138-153.
>
> If that title is taken at face value, would this not invalidate the
> premise that patterns of sequence divergences on a tree can be used
> to recognize species boundaries? The implication of the parenthetical
> phrase above is that morphology and ecology MUST be given primary
> credence, which runs contrary to what many seem to be preaching
> and/or practicing; that is, if it is admitted that barcodes alone are
> insufficient for the task of species delimitation, then what is the
> justification for studying and promoting barcodes alone? If good
> species can differ by one base pair, then (a) how could one *ever*
> know whether a single base pair difference is or is not indicative of
> a species-level difference without morphology to back it up, and (b)
> can we not therefore assume that there must be many cases where
> species have ZERO base pair differences (i.e., that barcodes are not
> unique, as claimed)? And, given that subspecies are typically
> morphologically distinct, then, by extension, barcodes could never
> help distinguish species from subspecies - only ecology (i.e.,
> breeding experiments, etc.) would be definitive - in which case
> barcoding is of rather more limited utility than its proponents
> generally claim; it would seem to come into play only if one has two
> otherwise very similar sets of organisms whose barcodes are
> *dramatically different*. That's certainly potentially useful in some
> contexts, but far from a solution to the "taxonomic impediment" as
> was initially claimed by Hebert, and only serves to enhance my
> already skeptical view of the barcoding enterprise.
>
> Or am I missing something here?
> --
>
> 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
>
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-- 
James B. Whitfield
Department of Entomology
320 Morrill Hall
505 S. Goodwin Avenue
University of Illinois
Urbana, IL 61801
http://www.life.illinois.edu/whitfield





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