From physiology to fitness: the costs of a defensive adaptation in rattlesnakes.

The costs of using and maintaining presumed adaptations are unknown for most animals. Energetically expensive traits, such as some agonistic and antipredator behaviors in animals, may incur trade-offs with other aspects of an animal's life history, such as feeding and reproduction. However, infrequent and brief use may reduce the costs of vigorous behaviors. The shaker muscles in the tails of rattlesnakes are an excellent system for studying the potential costs of a specialized defensive system. The high energetic cost of rattling may increase feeding requirements or use energy that could otherwise be available for reproduction. I used energetic modeling to test whether the cost of rattling in western diamond-backed rattlesnakes (Crotalus atrox) can be high enough to increase feeding demands or reduce fecundity and fitness. Only very frequent and prolonged rattling would increase feeding needs and perhaps reduce fecundity to some degree. Typically, rattling probably incurs very low costs to feeding, reproduction, and hence fitness. These and other results suggest that many seemingly expensive adaptations may have minimal costs to energy budgets, reproduction, and fitness.