Department of Earth and Biological Sciences
Faculty: William K. Hayes
Laboratory of behavioral ecology and conservation
G. Curtis Rehling (MS, 2002)
"Venom expenditure in multiple bites by rattlesnakes and cottonmouths."
Contact - Curtis graduated, moved to the northeast, and will be entering veterinary school in fall 2004.
Email: curtis@flyfishermen.com
The kids just love him... With excellent communication skills, Curtis was much appreciated for his ability to relate interesting facts to those of any age. Because few kids have an innate fear of snakes, we relish opportunities to share our knowledge with the next generation. Hopefully, they will treat snakes and their critical habitats with more respect than we do presently. Photograph: Shelton S. Herbert.
Curtis took on a hefty project, completing three separate experiments on venom expenditure during consecutive bites by not one, but two different species of snakes, the cottonmouth (Agkistrodon piscivorus) and southern Pacific rattlesnake (Crotalus helleri). Using two species actually doubled the amount of work involved and went against recommendations by his guidance committee. But hey...I like students with ambition! To quantify venom injected, he relied on three bite targets and simple protein assays. He compared the amounts of venom injected into each target for three consecutive bites. For predatory bites, he elected to use a mouse model consisting of a cheesecloth-covered, agar-filled condom that was similar in size, shape, warmth, and odor to a real mouse. Clever work. However, the snakes appeared to inject more venom into the model mice than other snake species have injected into real mice (in previous studies), so we can't help but wonder whether the model mice are treated the same as real mice. Even so, the consecutive bites represent a valid basis for comparison. For defensive bites, he used a warm, saline-filled glove to model a human limb in a low-threat context, and he created a high-threat context that entailed simple venom extraction involving physical grasping of the snake. His results proved to be very interesting. Read the abstract below.
You can also check out more facts regarding venom expenditure by visiting my account Research on Venom Expenditure and Strike Behavior by Snakes.
Thesis abstract
Venomous snakes have opportunities to bite multiple targets within a short time frame in nature. Thus, the ability to successfully inject multiple venom doses is of ecological importance. However, this capacity is limited by the quantity of venom available in the venom gland and the time required to regenerate it. This study was conducted to determine the envenomation strategies of two North American pitvipers (Agkistrodon piscivorus, Crotalus helleri) in multiple bites. Protein-based venom assay of non-biological bite targets was used to determine venom expenditure in multiple predatory, low-threat defensive, and high-threat defensive biting contexts. In the first experiment, mouse models were presented to elicit three sequential predatory bites. In this context, venom expenditure declined in successive bites and Crotalus helleri injected more venom overall than Agkistrodon piscivorus. The second experiment utilized saline-filled gloves to model multiple bites at a human limb, a low-threat defensive context. Venom expenditure declined with sequential bites for C. helleri but increased for A. piscivorus, suggesting that venom injection may be metered in defensive bites. Dry bites represented 16% of all bites at gloves, and were evenly distributed between species and among sequential bites. For the third experiment, voluntary venom extractions simulated a high-threat defensive context wherein the snake was grasped by an attacker. Venom expenditure declined for three successive bites, but unlike the first two experiments, A. piscivorus expended more venom than C. helleri. Duration of fang contact was positively correlated with venom in defensive strikes (experiment 2) but independent of venom injected in predatory strikes (experiment 1). This study also supports the importance of snake size as a determinant of venom expenditure, as found by previous authors. Though bite sequence had a significant effect on venom injected in all contexts, my results suggest that pitvipers have the capacity to deliver multiple potent bites.
Rehling, G. Curtis. 2002. Venom expenditure in multiple bites by rattlesnakes and cottonmouths. Unpublished MS thesis, Loma Linda University, Loma Linda, California.
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