Date of Award
Doctor of Philosophy
Ecology, Evolution, and Organismal Biology
Ecology and Evolutionary Biology
Fredric J. Janzen
Maternal effects are a ubiquitous source of phenotypic variation and relevant to understanding many ecological and evolutionary questions. For oviparous organisms, egg size and oviposition/ nest-site choice are two maternal effects that can be particularly important. A classic assumption in life-history theory is that offspring with more resources allocated to them have a fitness advantage, but this assumption is challenging to assess in the wild. Oviposition or nest-site choice can influence many aspects of the offspring environment including abiotic conditions, competition, predation risk, and food availability.
This dissertation focuses on the influence of egg size and nest-site choice on early life stages of the painted turtle, Chrysemys picta. Offspring of painted turtles at our study site in Illinois are laid as eggs in early summer and incubate for several months. Painted turtles exhibit temperature-dependent sex determination, where nest temperature during incubation irreversibly determines offspring sex. Consequently, as nest-site choice can influence nest temperatures, it can also influence offspring sex ratios. After hatching, offspring remain in the natal nest over the winter, and disperse to aquatic habitats the following spring. This dissertation has three data chapters, and together these chapters examine the influence of maternal effects on phenotypes and survival during incubation, hibernation and dispersal.
Data chapter two utilizes a cross-fostering design to partition the relative contribution of egg size, clutch effects, and nest environment to phenotypic variation. Additionally, I quantify the strength and form of selection acting on egg size and body size during incubation and dispersal, respectively.
Data chapters three and four describes an experiment where I compare siblings that incubate and hibernate in maternally-selected nest sites or randomly-selected nest sites. I examine the influence of nest-site choice on the nest environment, and on offspring sex ratio and survival during both stages. Additionally, I investigate the influence of nest-site choice on morphology and quantify the strength and form of selection during incubation and hibernation.
Collectively, these chapters provide evidence that larger offspring have higher survival during multiple life stages, and that sex-ratio selection is an important component of nest-site choice.
Timothy Staub Mitchell
Mitchell, Timothy Staub, "Phenotypic consequences of maternal effects during early life stages of the painted turtle, Chrysemys picta" (2013). Graduate Theses and Dissertations. 13153.