BGF wrote:
“In your view of taxonomy, what is the common ancestor of the elapids and how does this relate to the various lineages of colubrids. Also, how do you reconcile all 3FTx (elapid and colubrid) forming a monophyletic group relative to the abundant three-finger peptides in the body? If they were evolved independtly, wouldn't they form separate monophyletic groups (as is the case with the PLA2 toxins). “

According to Slowinski and Keogh’s tree (2000, Mol. Phylogenet. Evol. 15:157-164), Homoroselaps is the most basal elapid and the colubrids are ancestral to the elapids. The toxins they have in common probably arose in their common ancestor. Since most colubrids are not venomous, these chemicals most likely served other, as yet unknown purposes. Even though they are toxic, it does not automatically make them venom.

“But monophyletic groups is evidence of homology. This is the gold standard test.”

This is a circular argument, if the evidence of monophyly is a cladistic analysis. That is because cladists do not investigate homology separately. They assume that the characters they use are synapomorphic, and “test” this assumption using the tree they obtain from their phylogenetic analysis. That makes for a circular arguments since synapomorphy proves monophyly and monophyly in turn proves synapomorphy.

“Which is why we test this through phylogenetic analysis and the PLA2 toxins are a very useful control in this regard. If the 3FTx had been independtly recruited then they would have formed two separate groups like the PLA2s but they form one tight monophyletic group, hence the colubrid and elapid venoms share a history and venom evolved one time. This is not to say that new toxin types have not been added independently, like the independent addition of PLA2s, but this is because venom is a moveable feast. Changes in venom does not change the single origin.”

As Kenneth Kardong pointed out, venom is a biological definition, not a pharmocological one. Possessing a toxin does not make an animal venomous unless the toxic chemical is used to subdue or kill prey. A recent paper by Okumura et al (2002, Archives of Biochemistry and Biophysics 408: 124–130) shows that the nonvenomous colubrid snake Elaphe quadrivirgata has a PLA2 inhibitor in its blood, liver and lung. This protein inhibits group II PLA2 toxicity and enzymatic activity, and is only known previously in a viperid snake. Okumura et al. claims that this inhibitor may be widespread among snakes, even though they cannot rule out the possibility that it has evolved independently in E. quadrivirgata to counter the venom of the species of viperid that it occasionally preys upon. The presence of PLI beta in the lung, however, suggests to Okumura et al. that group II PLA2 is also present in the lung of Elaphe quadrivirgata, where it performs an as yet unknown physiological function. Their next project appears to be an investigation of the role of PLA2 in the lung of E. quadrivirgata.

“Please explain to me how you reconcile venomous and non-venomous colubrids with their common ancestor and what is the relationship of this ancestor with the elapids and vipers. Please also explain to me how two sea snake lineages independently evolving towards a non-venomous state is different than a lineage of colubrid evolving into a non-venomous state?”

As I said, different lineages of venomous snakes probably co-opted the same chemicals independently from their bodies for use in their venom. The elapids you mention show signs of a venomous ancestry; they have fangs and venom glands. Most colubrids lack fangs or grooved teeth and they also lack venom glands. Most colubrids, according to Kenneth Kardong’s estimate, do not even have a Duvernoy’s gland. The inferred presence of group II PLA2 in Elaphe quadrivirgata invalidates your “control.” This enzyme is either widespread among snakes, instead of being restricted to viperids as is previously thought, or else it evolved convergently in a nonvenomous snake and a venomous lineage. Either way, it shows that biochemical homoplasy is not only possible, but that it has indeed occurred within the Colubroidea. Therefore your hypothesis that biochemical similarity is evidence that venom evolved once in snakes is based on a falsified assumption. You will need much better evidence to show that your hypothesis is correct.

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