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

Richard Zander Richard.Zander at mobot.org
Wed Sep 16 13:04:15 CDT 2009

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


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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