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AFROTHERIA, CROWS & SPECIES CONCEPTS
Firstly, re: recent discussions of afrotherian monophyly.
While afrotherian monophyly has been widely accepted - in
part because it's intuitively pleasing (in fact the IUCN now
has an Afrotherian Specialist Group, formed in 2002),
neatly classifying some problem taxa - it's interesting to
note that some people who work on the taxa involved do
NOT find their data to support afrotherian monophyly as
favoured by Springer et al. (1997), Stanhope et al. (1998),
de Jong (1998), van Dijk et al. (2001), and others.
Consequently they are not so hot on the idea.
Robert Asher for example works on the cranial morphology
of tenrecs (which, with golden moles, form the Afrosoricida
component of Afrotheria: though note that Tenrecoidea
actually predates Afrosoricida and has the same
membership). His analyses of character distribution in
tenrecoids, other (traditional) insectivorans and other
mammals do not support an affinity of tenrecoids with other
afrotherians, and this is based on pretty robust
morphological evidence. To argue that Asher's data is
wrong and simply the result of homoplasy carries the
assumption that molecular evidence is inherently better than
morphological evidence. For all the details see...
Asher, R. J. 1999. A morphological basis for assessing the
phylogeny of the ?Tenrecoidea? (Mammalia, Lipotyphla).
_Cladistics_ 15, 231-252.
- . 2001. Cranial anatomy in tenrecid insectivorans:
character evolution across competing phylogenies.
_American Museum Novitates_ 3352, 1-54.
On European corvids David wrote...
In western Europe, there is a black crow usually called
*Corvus corone corone*. East of that, there's a middle-grey
one with black wings, usually called *Corvus corone
cornix*. (Probably they had different
refugia last ice age.) [snip]
_Perhaps_ the 2 are rather separate species, and the hybrids
have a somehow reduced fitness and therefore can't spread.
Perhaps not (they can and do breed). Nobody knows. The
term allospecies has been invented for this, in order to label
our ignorance. (Vienna is in the hybrid zone, although *C.
c. cornix* is most common here.)
Not to disagree with David but...
What is a species? A: whatever a systematist says it is.
Given that we 'know' that species are artificial (what we
regard as species are those segments of lineages we
recognise as distinctive), which forms are regarded as
species and which are not should be down to little more
than the consensus adopted by the workers involved. All the
different concepts of what a species is agree that the
distinctiveness of a form - whether or not it can be
diagnosed - is integral. The idea that species have to
maintain their integrity through space and time (a
component of the General Lineage Concept [GLC] and
some versions of the Evolutionary Species Concept [ESC]
but not of the Phylogenetic Species Concept [PSC] and
some versions of the ESC) is problematical given that
_Corvus corone corone_ and _C. c. cornix_ are diagnosably
distinct, differing consistently in plumage and vocalisation.
The hybrid zone between the two is historically stable,
having changed little in breadth (even if it has changed
position). This indicates that gene flow between the two
crows is restricted. Hybrids do have reduced fitness.
Accordingly, last year Knox et al. (2002) ruled that _C.
cornix_ is a separate species from _C. corone_.
Knox, A. G., Collinson, M., Helbig, A. J., Parkin, D. T. &
Sangster, G. 2002. Taxonomic recommendations for British
birds. _Ibis_ 144, 707-710.
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