[Taxacom] Justifying species?
mesibov at southcom.com.au
Sat Feb 16 20:47:20 CST 2008
In this recent paper:
Palmer, C.M., Trueman, J.H. & Yeates, D.K. 2007. Systematics of the
Apteropanorpidae (Insecta : Mecoptera) based on morphological and
molecular evidence. Invertebrate Systematics 21(6): 589-612.
the authors report what seems to be a routine systematic exercise:
cladistic analysis of a 36-character morphology dataset, COI sequence
data, and a combined morph/mol dataset, from 21 sampled populations of a
genus with two described species.
My query for the TAXACOM list is: is what follows also becoming routine
in systematics, or is it unusual?
What the authors do next is review their results in the light of at
least 6 different species concepts. For example, cladistic analysis
identifies a lowland clade of this mainly mountain-dwelling taxon. These
lowland populations have a distinct genitalic morphology, which 'agrees
with the potentially interbreeding biological species criterion of de
Queiroz (1988)'. 'As members of this clade also form a distinct cluster
of haplotypes, and form a diagnosable monophyletic group, this clade
also conforms to the genotypic cluster species definition of Mallet
(1995), and the autapomorphic (Donoghue 1985) and diagnosable
phylogenetic (Eldredge and Cracraft 1980; Cracraft 1983; Nixon and
Wheeler 1990) species concepts. These populations also inhabit a
different altitudinal range from all other members of the family, and
are therefore congruent with the ecological species concept of Van Valen
(1976), and the adaptive zone criterion of de Queiroz (1998). These
populations are therefore regarded as a distinct, undescribed species'
which the authors go on to describe in the formal taxonomic section of
their paper. They also describe a second new species because
'Adults of the population from Hartz Peak possess a unique combination
of morphological characters... Males from Hartz Peak also possess
distinct, readily diagnosable, genitalic autapomorphies... These
features of the genitalia indicate that this population is
reproductively isolated from all others. The haplotype of the Hartz Peak
population is also different from that of all other members of the
family, and constitutes its own, well-supported clade. The Hartz Peak
population therefore meets the biological species concept, autapomorphic
and diagnosable phylogenetic species concepts, and genotypic species
definition, and is regarded as a separate, undescribed species.'
Some (fill in the number of your choice here) years ago, a
morphology-only taxonomist presented with the same 21 samples might have
erected the two new species on genitalic differences alone, either
without worrying about species concepts or by assuming that genitalic
difference means reproductive isolation means two new BSC species.
Here we have taxonomists explicitly considering varied species concepts
and using their character evidence to build what I might call a
'defense' of their decision to erect new species. *In other words, the
more species concepts the taxon fits, the greater the justification for
naming it a Linnean species.*
I haven't seen this philosophical approach to erecting new species
before. Is it becoming more common now?
Dr Robert Mesibov
Honorary Research Associate, Queen Victoria Museum and Art Gallery
and School of Zoology, University of Tasmania
Contact: PO Box 101, Penguin, Tasmania, Australia 7316
(03) 64371195; 61 3 64371195
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