[Taxacom] FW: The 'reality' of species boundaries -- Once Again (UGHHH!)

Stephen Thorpe s.thorpe at auckland.ac.nz
Wed Sep 16 16:44:21 CDT 2009

Hi Richard:

Thanks for being perhaps the only one to still think this thread discusses anything important. Others seem to think "who cares what 'species' means? Let's just aggregate info on each of them!"
Anyway, a paper published just minutes ago in Zootaxa has some relevance:
I quote the abstract:

A recent phylogeographic study using mitochondrial and nuclear DNA revealed the presence of two well defined

allopatric clades of Blanus cinereus in the Iberian Peninsula. Using both univariate and multivariate statistical analyses,

we show evidence of morphological differentiation between the two clades. Despite the lack of visually diagnosable

morphological characters, the morphological and molecular data suggest that differentiation between the two clades was

significantly enough to prevent in the past gene flow and therefore to warrant a specific status for each of the two clades

This is another good example of BSC reasoning. Note "significantly enough to prevent in the past gene flow" (=reproductive incompatibility) "and therefore to warrant a specific status" ...

You say: An interesting point here is that many taxonomists who might not salute the biological species concept when asked about it actually "act as if . . . " in that they look for evidence of no or little gene flow

I agree. I think that is exactly what is happening! It has become "trendy" to slag-off the BSC, but you can't actually do much without it, so "call it something else, and keep your head down"! Like Jim Edwards' comment that looking at genitalia is really MSC because it is morphological differences in genitalia that you are looking for!


From: Richard Zander [Richard.Zander at mobot.org]
Sent: Thursday, 17 September 2009 6:04 a.m.
To: Stephen Thorpe
Cc: taxacom at mailman.nhm.ku.edu
Subject: RE: [Taxacom] FW: The 'reality' of species boundaries -- Once Again (UGHHH!)


By resolution of strong disagreements being valuable, I mean it is more than a goal, but a process. Watching how taxacomers at odds dance around intellectually, ducking and dodging until some clear point emerges at which they actually agree on definitions and (1) decide to agree to disagree by citing something really interesting, maybe different information or methods, or (2) give up, which points out something really interesting about the problem, or (3) agree, rarely and boring unless the reading also agrees.

I vivualize this as a stream of well-supported theory traversing time like a path in a dark jungle with battling scientists in a sense chopping a way through the undergrowth for that path.

Define cryptic species. If your definition is basically two or more species that are actually one species, I can't argue for or against, like the Trinity. Of course there are morphologically cryptic species that differ in other expressed traits, different major environmental adaptations, maybe considerably different larvae. If you are thinking two identical populations that differ only in some DNA sequence used to track lineage continuity, again there is a definitional problem about what is important in evolution such that classification should reflect it. In my various readings, nobody in evolution studies has dealt with the problem that one taxon can easily exist in two different molecular lineages, in spite of copious evidence that they often do. Phylogenetic monophyly (direct connection of descendant lineages with a shared ancestor) is quite different from evolutionary monophyly (sometimes gapped connection with a shared ancestor, such as in paraphyly).

How often do you yourself determine that the organisms you study have identical genomes, or genomic differences that are inferentially short of interfering with reproductive compatibility? An interesting point here is that many taxonomists who might not salute the biological species concept when asked about it actually "act as if . . . " in that they look for evidence of no or little gene flow, including gaps that represent gradualistic differential change. Much morphological analysis may well be looking for indirect evidence of little reproductive exchange. This is, of course, wrong. In my opinion. I think strong stabilizing selection is a major aspect of keeping, say, isolated populations of the same species looking, acting, and being alike and being the same taxon. Much the same procedure as looking for indirect evidence of reproductive isolation is involved in looking for evidence of unique stabilizing selection, so only the intent is wrong, not the outcome.

Richard H. Zander
Missouri Botanical Garden
PO Box 299
St. Louis, MO 63166 U.S.A.
richard.zander at mobot.org<mailto:richard.zander at mobot.org>

From: taxacom-bounces at mailman.nhm.ku.edu on behalf of Stephen Thorpe
Sent: Tue 9/15/2009 4:23 PM
To: Richard Zander
Cc: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] FW: The 'reality' of species boundaries -- Once Again (UGHHH!)

Hi Richard,
>Given that the resolution of strong disagreements is extraordinarily valuable in science
The "pot of gold at the end of the rainbow", perhaps?!
>Using reproductive compatibility as a criterion for species delimitation is okay only when it is practical, such as with birds and other big blundering beasts
Well, perhaps also with small blundering bugs! Explains the entomological fixation on genitalia. I can't really speak for plants, but I suspect that a proper understanding of BSC would in fact hold up.
>As far as I'm concerned, big changes in the genome that do not affect expressed traits are not important in classification, even if they interfer with reproductive compatibility
Then, what sense do you make of cryptic species? Particularly sympatric cryptic species, if you consider such a thing to be even a possibility?
Also, depends what you mean by classification. I don't count species-level taxonomy as classification per se. Classification is what we do to the species once we have them.
I would agree that big genomic changes that do not affect expressed traits are not important in classification or species circumscription, PROVIDED that they do NOT interfere (significantly) with reproductive compatibility

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