[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]


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 
species evolve.

_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.

Darren Naish
School of Earth & Environmental Sciences
University of Portsmouth UK, PO1 3QL

email: darren.naish@port.ac.uk
tel: 023 92846045