Date of Award
Doctor of Philosophy
Ecology, Evolution, and Organismal Biology
Ecology and Evolutionar y Biology
Females across taxa increase fitness by investing resources and care to offspring. However, numerous intrinsic and extrinsic factors influence both female and offspring performance and survival. Such complexity leads to tradeoffs in investment and variety in investment strategies. For iteroparous species, females must balance investment into reproduction with their own survival and future reproduction. In this dissertation, I examine how females balance numerous pressures on investment with an emphasis on how investment strategies vary across life.
In chapter two, I tested how maternal predation risk influences nest-site choice, and how maternal responses to risk affect offspring survival in painted turtles (Chrysemys picta). I compared young and old mothers to assess if response to risk varies depending upon maternal age. I predicted that young mothers would invest heavily in themselves (i.e., nest closer to the safety of water) whereas older mothers would invest more into current reproduction (i.e., nest farther from the shore because of lower nest predation risk). Contrary to predictions, neither young nor old females altered how far they nested from water after perceiving elevated risk. Nevertheless, older females nested farther from water than younger females, which is likely driven by lower future reproductive potential (i.e., residual reproductive value, RRV) in older females.
In chapter three, I assessed how offspring phenotype influences investment strategy in common snapping turtles (Chelydra serpentina). I released hatchling turtles at varying distances from water and monitored survival during overland dispersal. Survival decreased with dispersal distance. However, bigger hatchlings were less affected by increasing dispersal distance. Moreover, females producing larger and better dispersing offspring oviposited farther from water than females that produced smaller and poorer dispersing offspring. These findings suggest female investment can be sensitive to offspring phenotype and that such covariation between nest-site choice and offspring dispersal ability can maximize offspring survival and, thus, maternal fitness.
In chapter four, I examined how age and RRV compare in explaining variation in a risky investment behavior (i.e., distance females construct nests from water) in painted turtles. Previous work (in addition to chapter 2) has shown that older females nest farther from water than younger mothers and suggested this effect is driven by RRV. I predicted that RRV would explain more variation in distance to water than age because RRV accounts for any nonlinearity in future reproductive potential across age. Contrary to my prediction, age was a better predictor of nest distance to water than RRV. This finding suggests a stronger correlate of age (e.g., body size) may be more responsible for shaping the distance females nest from water than previously appreciated.
Collectively, this work suggests nest-site choice is a complex behavior that is shaped by numerous factors, many of which interact. Moreover, investment strategies shift across age to maximize lifetime fitness in freshwater turtles.
Delaney, David, "Causes and consequences of variation in maternal investment strategies" (2020). Graduate Theses and Dissertations. 18115.