Free Lunch Helps Rattlesnakes In Mating Game

FAYETTEVILLE, Ark. - For a certain group of rattlesnakes in the Arkansas Ozarks, there is such a thing as a free lunch—and that lunch has helped University of Arkansas scientists learn more about the physiology of these reptiles.

Steven J. Beaupre, associate professor of biological sciences, combines fieldwork, laboratory work and computer simulations to get a better perspective on how future changes in climate and environment may affect these reptiles. The National Science Foundation recently awarded him a second consecutive grant to continue his rattlesnake studies.

Snakes make good models for studying behavioral and physiological ecology because their behaviors are easy to see: A foraging snake holds its head differently from a resting snake, and snakes seeking mates are found in different positions and locations than resting or foraging snakes. Also, researchers can tell when a snake has eaten by the telltale bulge in its otherwise lithe body.

Beaupre and his colleagues supplemented the resources of one small group of rattlesnakes by feeding them rats that have been frozen and thawed. They simultaneously followed a group of rattlesnakes that did their own foraging. The snakes with supplemented diets averaged about four times more energy from meals than their counterparts.

Since 1998, the researchers have used radio telemetry to track the movement of all the snakes, periodically checking the snakes’ growth and behaviors.

They found out that when it comes to reproducing, size does matter—at least for snakes. Snakes with additional food spent more time digesting, and larger males courted females about twice as often as their less-fed competitors.

"These are truly food limited organisms," Beaupre said. It takes rattlesnakes 8-10 years to reach maturity in the wild, but supplemental feeding may cause the snakes to reach sexual maturity earlier.

This finding fits well with Beaupre’s simulated snake model. Beaupre has developed a computer model that simulates rattlesnake behavior and physiology. The model allows the user to manipulate different aspects of a snake’s life, such as body temperature, food availability, metabolism and digestion, to determine any effects on growth, size and reproduction for the animals.

The model, based on data generated on different types of snakes, has shown that an increased food supply can speed growth and help with reproductive success.

In addition, the model suggests an optimum size for breeding female snakes. Female rattlesnakes that mature at medium sizes have the highest reproductive output. Smaller females have less room to accommodate developing offspring and eat smaller meals. However, very large females spend too much of their limited energy in support of metabolically expensive body tissue - leaving less energy available for making offspring.

Another reason Beaupre simulates snake behavior is to find out what information he lacks.

"You find out quickly what you don’t know about how an animal works," Beaupre said.

He and his graduate students measure physiological indicators in the laboratory and in the field using oxygen isotopes and deuterium to measure water lost in respiration and metabolic rates. They can then look at the physiology, size, condition, behavior and environment of the snake to determine how these factors affect one another. They also can incorporate data on individual snakes into the snake simulator to look at entire populations.

Up to this point, Beaupre and his colleagues have focused on the physiology and energy budgets of male snakes.

"Males are simple," he said. "They don’t have the complication of larger energy allocation to reproduction."

With renewed NSF funding, Beaupre plans to study the reproductive energetics of female rattlesnakes. He will incorporate his findings on the individual male and female rattlesnakes into the computer model to generate an ever more accurate tool to predict physiological and behavioral changes.

"These things are at the core of understanding what will happen to the population" as climate and other environmental changes occur, Beaupre said.