BGF wroet:

“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.“



You are laboring under a misunderstanding of ratsnake evolution. Let me briefly summarize the available evidence on ratsnake evolution. The racers (e.g. Coluber, Ptyas, Gonoysoma, Masticophis) are either the paraphyletic parental group which gave rise to the ratsnakes (e.g. Old and New World Elaphe, Lampropeltis, Arizona, Bogertophis, Pituophis) or these two groups are monophyletic (holophyletic) sister groups that share a common ancestor. Unfortunately the systematic position of Elaphe [“Coelognathus”] radiata remains unclear because Utiger et al. excluded all species of “Coelognathus” from their otherwise rather comprehensive analysis. Therefore there are two scenarios:



“Coelognathus” is a racer. In that case, either the common ancestor of racers and ratsnakes is non-venomous, which disproves your theory that the colubroid ancestor is venomous, or the common ancestor of the racers and ratsnakes is venomous and the genus Elaphe has since lost its venomous ancestry completely without a trace.



The second possibility is that “Coelognathus” is a ratsnake. In that case it would mean that either venom evolved independently multiple times in Colubroidea, which of course falsifies your hypothesis, or else “Coelognathus” underwent the following evolutionary sequence:



nonvenomous (booid ancestor) -> venomous (colubroid ancestor) -> nonvenomous (ratsnake ancestor) -> venomous (Elaphe radiata).



You seem to favor the hypothesis that “Coelognathus” is a racer, but that would contradict your earlier claim that it is a ratsnake and that the ratsnakes lost their venom. If “Colognathus” is a racer, then there is not a single species of ratsnake that is venomous. It also means that there is no reason to suppose that either their ancestor or the colubroid ancestor is venomous. There is no “fatal flaw” in my argument. You are simply mistaken about ratsnake and racer relationships.



“As for homoplasy, this is disproven by the phylogenetic analysis unless you want to argue against phylogenics as a whole. “



As Feduccia points out, convergent evolution is an insidious trap. It appears that you have fallen into that trap.



“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. “



Did I not already point out to you that biochemical homoplasy is rampant in eye evolution? Why would you still insist that venom evolution must follow the most parsimonious route according to these chemicals? Besides, the “Coelognathus” problem I discussed above shows that it is simply not parsimonious for venom to have evolved once, since it would need to evolve twice if “Coelognathus” is a ratsnake, and if it is racer, then the common ancestor of the ratsnakes almost certainly is nonvenomous, meaning that the colubroid ancestor is also likely to be nonvenomous.



“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. “



See the “Coelognathus” problem above to see why venom most likely did not evolve in the colubroid ancestor.



“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. “



Far from being evidence free, the multiple recruitment theory is supported by the evolution of other body parts, including the eye. I am not sure how multiple recruitments can result in monophyletic groups for the toxins due to homoplasy. That is not a logical extension of the multiple independent evolution of venom. Therefore you are only erecting a strawman. I point out that convergence can result in similar chemical structures among related taxa.



“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 “



I have no difficulty understanding the basis of your hypothesis. You are fooled by the chemical similarities of the venoms of different lineages, not realizing that similar chemical structure can result even when they are products of convergent evolution. I showed you how it happened in the evolution of the eye, but you simply ignores it and continue to have blind faith in these similarities. We all have eyes, but only some of us will use them to see evidence of convergent evolution.

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