So, first paper:
I promised pretty pictures and phylogeny, here’s the phylogeny:
From: Phylogeography of the pitviper clade Agkistrodon: historical ecology, species status, and conservation of cantils, Parkinson et al. 2000
This is from the paper that originally proposed A. taylori be reclassified as a distinct species from A. bilineatus. Note that it also supports A. taylori being the outgroup among the other subspecies of A. bilineatus. This supports the trans-continental model of this genus’ evolution. The article also provides some pretty good ideas on conservation of neotropical Agkistrodons. Essentially, the trans-continental model is probably correct, A. taylori is a separate species, we need to protect the Central American and Mexican Agkistrodons.
Let the sex begin!
The first paper is by Dustin Siegel in Sever’s lab. (I only know this because he was at a convention I attended)
They looked at oviduct seasonal variation. Who cares, right? Well, it has implications in understanding the reproduction of many organisms, not just this one species. Organisms with similar mating patterns and sperm storage may have similar seasonal variation. It also makes damn interesting party conversation. Picture said researcher trying to pick up a date and then they get to that “oh, you do research, in what?” “sperm storage.” If said researcher is male, he will be slapped, if said researcher is pretty and female, well…
Anyway, here’s the research:
This was really a multi-part experiment involving histochemistry and electron microscopy building on previous research. Unlike other squamates, A. piscivorous still has those specialized uterine glands similar to those found in oviparous species responsible for egg-shell formation and differ even amongst ovoviviparous squamates. Another neat part is that the locations for sperm storage in this species are highly specialized, secreting a cocktail to keep sperm alive. In addition to this, reproductive cycles of this species were also investigated and numerous questions were raised such as homology to similar features in other squamates as well as a possible role of mating order with fertilization. We still have quite a bit to learn about the behavior of this species, as we will see shortly.
Fig. 1. Follicle development and embryogenic cycle in female Agkistrodon piscivorus. (A) Ovarian follicle size in postpartum to late summer/fall mating season females (example: August 2005– September 2006). (B) Ovarian follicle size immediately prior to hibernation (example: November 2006). (C) Ovarian follicle size shortly after emergence from hibernation (example: March 2007). (D) Ovarian follicle size immediately prior to ovulation (example: May 2007). (E) Near fully developed embryo removed from uterus in August (gravidity would occur from May to August/September).
Fig. 11. Reproductive cycle of female Agkistrodon piscivorus (redrawn from Aldridge and Duvall, 2002). Biennial cycle of reproduction in A. piscivorus females results in two possible reproductive conditions in each month (A or B). Povd sperm, sperm presence in the posterior
oviduct; SST sperm, sperm presence in SSTs; SST activity, secretory activity of sperm storage tubules; Utg activity, uterine gland secretory activity.
Since I know everyone is just dying to see what a snake reproductive tract looks like:
Fig. 1. The four recognized regions of the female Agkistrodon piscivorus oviduct discussed in this study. Gu, glandular uterus; Inf, infundibulum; Ngu, nonglandular uterus; Ov, ovary; Vag, vagina.
This is from the same paper, published in a different journal, I’m not sure exactly why it was not included in both…
Can anyone tell me at what stage this female is at? Hint, you have a key two photos up…
We move along to Glaudas et al. in Migration patterns in a population of cottonmouths (Agkistrodon piscivorus) inhabiting an isolated wetland. Snakes going to the habitat were highly directional. This is not surprising since many individuals will hibernate in the same location year after year. Most of them left from October to November with juveniles leaving first. They propose several reasons for this varying from predators to the time required for suitable habitat. Another interesting observation is that adult snakes leaving the habitat were highly directional in the southwest direction. The high rates of arrivals were from northeast (males, females, and juveniles) and southwest (females only) while the high rates of departures were southwest (males and females) and undirectional (juveniles). Peak migration times were March arrivals (males, females, and juveniles), July departures (females), October (juvenile) departures and November (male and the remaining females) departures.
Anyway, the main point to take away from this is that these snakes make considerable use of land near their summer habitat. This means that conservation of this species not only requires preservation of aquatic habitat, but also distinct forested corridors around this habitate for overwintering.
Comparisons of Aquatic Versus Terrestrial Predatory Strikes in the Pitviper, Agkistrodon piscivorus. Vincent et al.
Long story short, I could ramble about this one for days, is that A. piscivorus, while it does frequently eat fish, sucks at catching them. The snake frequently did not get their fangs into the fish that was struck at and of the fifty-four aquatic strikes observed, only seven were successful. It is possible that the conditions simulated were the results of a very hungry snake with no other prey around being forced to strike at a longer distance than would be done normally as a result of hunger. Nevertheless, there were interesting observations, namely that terrestrial and aquatic strike velocity and acceleration did not vary and that aquatic strikes were usually done further from the prey rather than closer. It does pose some interesting questions though, namely why the increase in distance from terrestrial to aquatic strikes and how are the speeds through water and through air the same? In most aquatic strikes, the snake ended up striking above the fish with only the lower jaw ever making contact and fangs never puncturing. Contrast this to terrestrial strikes where the fangs were the initial point of contact and you can see why the strike success rates varied.
More on snake sex!
In case you don’t know, male snakes have two penes (plural of penis) with each being called a hemipene or “half penis.” I’m really only telling you this to give you an idea of how the fuck in all of these papers did they know 1) which ones to dissect and 2) which ones were male or female in the migration study. Well, one of several ways are usually done.
Cloacal probing is done by inserting a probe into the cloaca of the animal and towards the tale and if it easily slides considerably deep into the tail, it’s a male. Snakes are usually placed in tubes so that the person doing said probing doesn’t experience a few probes in the form of fangs.
Now, here’s what makes learning about cloacal probing pays off with something useful with Vincent et al. again. This time, Sexual dimorphism in head shape and diet in the cottonmouth snake (Agkistrodon piscivorus). Males and females of A. piscivorus vary in diet. This means that they are subject to varying selective pressures for gape, head size, and body size. Males, since they eat larger prey, require a larger quadrate bone to allow for a wider gape. Why on earth would a single little bone have such an effect on the gape angle? Well, the quadrate bone is a pivot point. If the quadrate bone is longer, it allows the jaw to open wider.
Now to tackle the actual problem of prey “size.” What is the size of prey, is it the volume, the mass, or the widest point? Well, for this study, “size” is measured by the height of the animal. Males and females at fish at about the same frequency, but males ate far larger fish than females. Females ate reptiles over twice the frequently of males and this, along with fish, made up the bulk mass of female prey items with amphibians getting about 10%. The bulk mass of male items came from fish, reptiles, and amphibians combined. These data mean that while fish account for the same proportion of animals by number, account for far larger percentages in males, while females ate larger reptiles such as lizards and other snakes. Males, therefor, need a larger gape to accommodate this larger prey size.
- Phylogeography of the pitviper clade Agkistrodon: historical ecology, species status, and conservation of cantils. Parkinson et al. Molecular Ecology (2000) 9, 411–420
- Seasonal Variation in the Oviduct of Female Agkistrodon piscivorus (Reptilia:Squamata): An Ultrastructural Investigation. Siegel et al. Journal of Morphology (2008) 269:980–997
- Comparisons of Aquatic Versus Terrestrial Predatory Strikes in the Pitviper, Agkistrodon piscivorus. Vincent et al. Journal of Experimental Zoology (2005)303A:476–488
- Migration patterns in a population of cottonmouths (Agkistrodon piscivorus) inhabiting an isolated wetland. Glaudas et al. (2006) 271-2:119 – 124
- Sexual dimorphism in head shape and diet in the cottonmouth snake (Agkistrodon piscivorus). Vincent et al. J. Zool., Lond. (2004) 264: 53–59