Risk-sensitive maternal investment: an evaluation of parent–offspring conflict over nest site choice in the wild

Abstract

Parents increase their fitness by investing resources in offspring. However, such investment is costly for parents, leading to trade-offs, which should shift towards heavier investment in reproduction as females age and future reproductive opportunities decrease. Nests of aquatic turtles laid farther from water have higher survival than those laid closer to shore because nest predators often forage along environmental edges. However, the predation risk of adult females increases farther from water because water is used as refuge from terrestrial predators. Thus, females may balance investment in current offspring versus maternal survival and future offspring. To test whether investment varies depending upon perceived risk, we exposed 30 painted turtles, Chrysemys picta, to simulated predation by capturing and handling them shortly after females chose a nest site. We then released females, which fled to water, and allowed them to return to land and nest undisturbed. We compared the distance to water of nests laid before and after simulated predation. Unexpectedly, females did not vary distance to water in response to simulated predation. Regardless, nest sites chosen after simulated predation were more likely to be depredated than those chosen before simulated predation, suggesting that females altered nest site choice in ways we did not quantify. In addition, although older turtles nested almost twice as far from water as younger turtles, we found no evidence that age influenced maternal response to simulated predation. Our findings suggest that perceived risk of mothers to predation influences nest site choice and subsequently reduces offspring survival in C. picta. In addition, we provide a rare assessment of how plastic maternal investment might vary across reproductive life.