Real species and ideology

[Barry Roth]

christian thompson <cthompson at SEL.BARC.USDA.GOV> wrote:

So, I would suggest that we all return to the arguments of Wilson &
Brown of the 1950s and just abandon subspecies at least in terms of
"real," or naming. And declare what is of interest and importance is
variation: the differences between individuals which we hypothesize
belong to "species" and how that relates to the whole, etc. Anything
else leaves us in a mess political situation.

In Roth, B. 2004 Observations on the Taxonomy and Range of Hesperarion Simroth, 1891 and the Evidence for Genital Polymorphism in Ariolimax Mörch, 1860 (Gastropoda:  Pulmonata:  Arionidae:  Ariolimacinae). The Veliger 47:38-46, I wrote:

     Most land mollusk taxonomy over the past sixty or seventy years has been practiced ostensibly with reference to the “Biological Species Concept” (Mayr, 1940)[1] or its immediate predecessors (e.g., Dobzhansky, 1937; see, for example, Pilsbry, 1939: xiv).  In practice, observations of presence or absence of interbreeding have rarely been attempted.  More often, the judgment of what is a particular land snail or slug species has been based on degree of difference criteria and the distribution of character states through an array of specimens, or on other circumstantial evidence of reproductive isolation such as differing genital morphology.

     For purposes of this report, a species comprises all the individual organisms predicted on the basis of available evidence to prove to compose a least inclusive monophyletic unit recognized in a formal phylogenetic analysis.  It is expected that upon such analysis this aggregation of individuals will conform to the species concept of Mishler & Theriot (2000), grouping together as a taxon because of evidence of monophyly.  The relevant evidence of monophyly is apomorphic character states.  This definition generates a hypothesis about the way such an analysis will turn out.  The result of a phylogenetic analysis is itself a hypothesis about the true historical relationships among its taxa.  Because for most clades of North American land mollusks, species-level phylogenetic analysis has not yet been performed, this is a “working” definition.  But I believe taxa thus recognized will prove the most useful units for estimates of biodiversity, ecological studies, conservation and
 management decisions, and other end uses of taxonomy.

     The taxonomy of North American land mollusks inherited from Pilsbry (1939-1948) and his successors includes numerous subspecies, also recognized on degree of phenetic difference, subjectively judged.[2]  There is no generally agreed-on rule regarding their formal taxonomic recognition, and for reasons articulated by Wilson & Brown (1953) there are unlikely to be any.  I agree with proponents of phylogenetic species concepts (e.g., Mishler & Theriot, 2000; Wheeler & Platnick, 2000) that the least inclusive taxon in formal taxonomy should be the species, and that where they exist, well-defined, diagnosable “subspecies” should simply be called species.  What is “well defined” remains a taxonomist’s judgment call, but arbitrary decisions on rank are less a factor than before.  With improved methods of study, many western North American taxa formerly ranked as subspecies have been shown to have attributes such as genital differences that mark them as species even under the Biological
 Species Concept (Roth & Miller, 1993, 1995).


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[1] “Species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups” (Mayr, 1940).  For additional critiques of the concept, and reciprocal criticism of phylogenetic species concepts, see Wheeler & Meier (2000).


[2] “Most subspecies are recognizably differentiated populations which are not considered sufficiently distinct to be called species” (Pilsbry, 1939: xiv).  “In ambiguous situations it is … advantageous to treat allopatric populations of doubtful rank as subspecies” (Mayr, 2000: 26).

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I don't expect that all readers will buy in to this model (and I have already received some -- in my opinion ill-considered -- responses), but I can tell you that I enjoy systematic practice more since I have stopped trying to tell my readers, in effect, "pay no attention to that man behind the curtain" regarding species/subspecies assignments.  It was astonishing to me to read that in year 2000 Mayr still recommended subspecies as a waffle "in ambiguous situations."



Barry Roth




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