01
Oct
08

Agkistrodons-review part 1

I’ll start with saying this will be finished soon, it’s a rough draft, so if you find errors, correct me. I was trying to finish my summaries before Tangled Bank came out, but I failed… I’ve previously done some backyard blogging on the natural history and behavior of Anoles and Hylids, like how Anoles love to do some exercise instead of fight and are often mistakenly called “chameleons” because they can change color. I suppose, in that tradition, I’ll start out with a bit of natural history for you. Many of you have heard of “water moccasins” or “cottonmouths,” but sometimes the former can be rather ambiguous. Agkistrodon piscivorus is sometimes called a “water moccasin” while other times this is often used to refer to the relatively harmless Nerodia genus (frequently, it’s just a Diamondback Water Snake in my area). The difference is quite substantial when you consider one may kill you, and the other may just lead to a nasty infection, easily treatable with antibiotics.

Now that we’ve gotten that out of the way, time for the first Agkistrodon I will talk about in detail.

Agkistrodon bilineatus (Cantil). You may ask why, but the answer is simple, it is relatively central in the phylogeny. It is closely related to Agkistrodon taylori and Agkistrodon piscivorous. So let’s talk a bit about it.

A. bilineatus is found scattered about Mexico and Central America with various subspecies that are recognized. Like all of this genus (and most in the Crotalinae subfamily), they are ovoviviparous (something which I always thought was neat). (The two genera of Crotalids which are oviparous are Lachesis and Calloselasma) Some of the venom proteins have implications in medicine, particularly those that trigger agglutination. (Lu et al.) Such proteins may be used for rapid coagulation of cuts or scrapes. Many possible evolutionary reasons for this may exist, I shall not speculate on this further aside from suggesting the possibility that they served to further reduce active platelets.

A. taylori was originally classified as a subspecies of A. bilineatus but, based upon mitochondrial evidence, was brought to species status. (Parkinson et al. 2000) A. taylori and A. bilineatus also have very a similar LD50.

A. piscivorus is the species I first wrote about. This is also the one I am most familiar with the effects of, having been hospitalized for a bite from this quite painful species. (stupid mistake on my part) This species is the only one known to actively catch fish, (hence the name) and it has tends to hold on to prey rather than inject venom and release like many vipers. While swimming on the surface of the water, this species is demonstrably higher in the water than Nerodia species generally keeping the entire dorsal surface above the water while Nerodia will keep far less above the water. Nerodia species also have eyes located towards the top of the head (similar to crocodiles) while A. piscivorus has eyes located on the sides of the head. I always look at the head shape of swimming snakes.

A. contortix has many venoms being studied by Dr. Markland at USC. Chief among these is contortrostatin, a small disintegrin (targets αVβ3, among other things, if I remember correctly) that may be useful in understanding the role of integrins in tumors. I certainly hope Dr. Markland’s work is fruitful in this endeavor. Another interesting aspect of this species is that it has a fondness for cicadas. This species (generally) has a venom which is far less toxic to humans.

*Note: any species you see from outside of the Americas is not an Agkistrodon!

In part 2, I’ll have some summaries from five different papers, but I wanted to at least have my introduction up.

Topics which I will be discussing are: phylogeny, dimorphism, reproduction, migration, and even more reproduction. Dr. Sever loves sperm! Amazing to listen to him speak as well.

Part 2 may not be quite finished until October 1 at 1PM CST


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