Posted by:
BGF
at Sun Nov 2 03:12:17 2003 [ Email Message ] [ Show All Posts by BGF ]
The fatal flaw with your scenario is that it assumes that Coelognathus post-dates the evolution of the American Lampropeltis/Patherophis/Pituophis lineage when in fact all the American colubrines are descended from Asian invaders. Thus, mapping over the taxonomical tree shows that venom evolved a single time, was lost in the American lineage and then thats it. Not too terribly difficult to follow unless you are deliberately (for reasons that only you know) putting on the blinkers.
As for homoplasy, this is disproven by the phylogenetic analysis unless you want to argue against phylogenics as a whole. In which case I would like to see how you would explain PLA2 toxins obviously having been involved twice in snake venoms, once in the Viperidae (through recruitment of a synovial (type II) phopholipase gene for use in the venom and another time by the common ancestor of elapids 'colubrids' through the recruitment of a pancreatic (type I) phospholipase gene into the chemical arsenal. When analysed by bayesian, maximum parsimony and neighbor-joining, the two toxin types for two separate monophyletic groups, with an abundance of non-venom proteins in between. In contrast, the 3FTx, CRISP, cystatin, nerve growth factors, M12B peptidases, ANP/BNP-toxins form monophyletic groups, obviously indicative of a shared history and consequently recruitment of into the venom right at the base of the Colubroidea tree. This shows not only that venom evolved a single time but also which toxins were part of this first recruitment. Further evidence against homoplasy is the CNP-toxins represent a second recruitment of natriuretic pepetides into the venom and form a monophyletic group distinct from the ANP/BNP toxins. This demonstrates quite nicely that natriuretic peptides were recruited twice into the venom. Similarly, the lectin toxins form two monophyletic groups, once as an ancestral type and a second when recruited again into the viper venoms.
According to your evidence-free theory, if there were multiple recruitements then all the toxin should form monophyletic groups due to homoplasy. We have demonstrated that this simply is not the case.
I fail to understand why you are having such a hard time grasping this but really don't care actually. However, it does provide a perfect backdrop for our results since you are a lovely example of the wrong interpretation.
Thanks mate, couldn't have done it without ya 
Ciao
B
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Dr. Bryan Grieg Fry
Deputy Director
Australian Venom Research Unit
University of Melbourne
www.venomdoc.com
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RE: Elaphe ["Coelognathus"] radiata - BGF, Sun Nov 2 03:12:17 2003