Scott,
I was glad to see your reply here on this thread.
Let me say from the outset that I enjoyed your new book on "colubrid" venoms and bites, which brings together a tremendous amount of data and provides a tremendous resource for anyone interested in this topic - it is an absolutely 100% recommended must-read as far as I am concerned. There are very few specialist books for which I make time to read the whole thing cover-to-cover, but this was one of that select few. Please bear this big picture in mind while I quibble about a couple of evolutionary points in the following paragraphs
If I may be a little tongue in cheek about this, while I found the book extraordinarily informative, I could not help deriving considerable amusement from the intellectual contortions involved in avoiding that nasty V-word for the "Duvernoy's"/venom gland secretions of the vast majority of non-front-fanged colubroids. There are several facets to this:
1. You want to see evidence that snakes use their secretions for subduing prey or for defence. That evidence exists for only for a small minority of non-front-fanged colubroids, true. However, for how many is there
actual evidence that they do
NOT use these secretions?
I think there some confusion there between absence of evidence and evidence of absence. Bruce Young's recent "Tears of venom" paper showed very elegantly how a non-canaliculate venom delivery system can inject venom fairly effectively, even as a low-pressure system. I agree entirely that we desperately need more case studies of what non-front-fanged snakes (and lizards for that matter) do with their secretions, but the "If it is not demonstrated to be used for prey capture or defence, then it isn't venom" attitude seems to me to be the wrong default position. Given the homology of toxins, glands and teeth, I would suggest that the burden of proof is on those who argue that we should
not call them the same thing.
2. You repeatedly mention and explicitly adhere to the traditional definition of venom, being based largely on biological function. The problem with traditional definitions is that their relevance can become problematic as new evidence, new methods and new conceptual approaches provide us with new ways of looking at problems, leading to paradigm shifts. Look at taxonomy: since the 1950s, we have moved from an approach based largely on similarity to one based strictly on evolutionary relationships, and the reason for this is that newer conceptual outlooks and methodological tools have given us new insights that we have incorporated in the way we do taxonomy. In a nutshell, taxa are now defined on the basis of evolutionary relationships, specifically on the basis of monophyly. You clearly (and quite rightly) accept this, since the book talks about "non-front-fanged colubroids" rather than "colubrids", acknowledging the non-monophyly of what was the family "Colubridae" of old.
To me, this now begs a simple question: why should the definition of venom be immune from paradigm shifts? Before we had the level of evidence of evolutionary homology of glands, teeth and toxins available today, it was perhaps reasonable to define venom and venomousness purely on a functional/anatomic basis, with some taxa having that feature, whereas others lack it. However, we have moved on from that. We have an abundance of data that show all venom/"Duvernoy's" glands to be homologous, that show all snake fangs to be homologous, and that show many toxin families to be homologous across all Colubroids. As an evolutionary biologist, I would find it extremely peculiar to ignore and exclude this large body of evidence and the consequent new view of the evolution and origin of venom from the question of how we define venom. To me, this would be the intellectual equivalent of continuing to recognise the "Colubridae" of old as a single family due to the shared primitive lack of front fangs despite the fact that their non-monophyly is rejected by an increasingly large body of evidence.
3. I fail to see how the traditional definition would be helpful in practice. Where we have two closely related species of snakes using homologous teeth to inject a homologous secretion into a prey item, is it really helpful to expect us to stand with a stopwatch and time the subsequent events before deciding that one of them is venomous and the other one perhaps not, based on some arbitrary threshold? Does it make sense to call one species of garter snake (for the sake of argument) venomous because its secretions have an effect beyond a certain arbitrary threshold, whereas those of another, closely related species fall just short? As always in evolutionary biology, we are almost certainly dealing with a continuum of function. Acknowledging evolutionary homology in our terminology seems to make a lot more sense than drawing arbitrary lines, especially when we have no evidence to even do that for the vast majority of species.
4. We need to be careful about letting the potential public impact of terminology dictate the technical language of science. I appreciate that "venom" and "venomous" are emotive words, considering the general public's attitudes towards snakes. However, the simple fact is that the majority of advanced snakes (just like virtually all spiders) fall into the category of "venomous but harmless". Since all spiders (except for one or two small families) use venom to capture their prey, you presumably agree that they are venomous, and hence, calling them non-venomous would be biologically misleading. Exactly the same applies to the majority of advanced snakes. So, if I were to write a field guide for the general public, I would simply categorise a garter snake as "harmless" (given the rarity and often special circumstances surrounding the very minute percentage of symptomatic bites, such as the one that triggered this thread), and a rattlesnake as "dangerously venomous" - it avoids alarming anyone or sensationalising the issue, but provides the information that the general public really need and want to know.
At the end of the day, there will probably never be full agreement on the definition of venom, and I don't have a simple solution. However, I don't think that going back to a definition of venom that ignores the increasingly vast body of evolutionary evidence is going to be helpful to the understanding of these secretions.
Best wishes,
Wolfgang Wüster
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