PHENOTYPIC COVARIATION OF CARAPACE MORPHOLOGY AND NESTING BEHAVIOR IN THE PAINTED TURTLE
Daniela Flores1, Jaymie Reneker2, Daniel Warner3, Fredric Janzen1.
1Iowa State University, Ames, IA, 2University of North Carolina Wilmington, Wilmington, NC, 3The University of Alabama at Birmingham, Birmingham, AL.
Parental care varies across vertebrate taxa, ranging vastly from high-input care in mammals to very limited care in some reptiles. In some oviparous species, such as the painted turtle (Chrysemys picta), parental care is limited solely to maternal effects in terms of egg size, yolk hormones, and nest microenvironment. Maternal nest-site choice is especially critical in species like C. picta that have temperature-dependent sex determination, in which incubation temperatures permanently dictates the sex of the offspring. This project combined field and laboratory studies to examine morphological indicators of a female’s nesting behavior and clutch sex ratio in C. picta. Nesting females in the field were characterized as flat, domed, or intermediate based on carapace measurements. Vegetation coverage of each nest site was quantified, and sex ratios were obtained after egg incubation either in the field in their natural nests or in the lab at a temperature to produce both sexes. Carapace morphology was associated with nest-site choice, with more domed females nesting in shadier sites and flatter females nesting in sites with more direct sunlight. Carapace morphology and clutch sex ratio were associated only when eggs were incubated in their natural nests. This result was not mirrored in the lab experiment, implying that the primary influence on clutch sex ratio is a nest’s vegetation coverage. These results highlight a unique example of a morphology-behavior relationship in vertebrates that may influence population structure and fitness.