Behavioral Modification as a Means of Reducing the Cost of Reproduction

Abstract

Because relative clutch mass (RCM) adversely affects locomotor performance, and therefore presumably the survival rate of pregnant females, it is assumed to be constrained by natural selection. I propose that changes in antipredator tactics during pregnancy can reduce females' dependence on locomotion, thereby alleviating selection acting on RCM. Such a behavioral shift would be a more likely response to selection against poor locomotor ability because reductions in RCM have obvious disadvantages (i.e., decreasing fecundity) and can only partially improve speed and endurance. Comparisons of the locomotor performance and antipredator behaviors of pregnant female garter snakes (Thamnophis ordinoides) before and after parturition indicate that locomotor ability declines and that antipredator tactics change during gestation. Females tend more toward cryptic behavior during pregnancy than after. These observations are consistent with behavioral shifts observed in lizards during periods of reduced locomotor ability.