Because resources are finite, female animals face trade-offs between the size and number of offspring they are able to produce during a single reproductive event. Optimal egg size (OES) theory predicts that any increase in resources allocated to reproduction should increase clutch size with minimal effects on egg size. Variations of OES predict that egg size should be optimized, although not necessarily constant across a population, because optimality is contingent on maternal phenotypes, such as body size and morphology, and recent environmental conditions. We examined the relationships among body size variables (pelvic aperture width, caudal gap height, and plastron length), clutch size, and egg width of diamondback terrapins from separate but proximate populations at Kiawah Island and Edisto Island, South Carolina. We found that terrapins do not meet some of the predictions of OES theory. Both populations exhibited greater variation in egg size among clutches than within, suggesting an absence of optimization except as it may relate to phenotype/habitat matching. We found that egg size appeared to be constrained by more than just pelvic aperture width in Kiawah terrapins but not in the Edisto population. Terrapins at Edisto appeared to exhibit osteokinesis in the caudal region of their shells, which may aid in the oviposition of large eggs.

Studies examining the association between life-history strategies and behavior can help inform our understanding of the fitness consequences of reproductive behaviors. Breeding migrations are common in numerous taxa and often represent an important reproductive cost. We examined body mass changes of spotted salamanders (Ambystoma maculatum) during their seasonal breeding migrations to determine the influence of breeding behaviors on reproductive costs. We sampled salamanders entering and exiting a 0.92-ha ephemeral wetland in the North Carolina Piedmont using a 400-m drift fence completely encircling the wetland. Traps were checked daily during annual breeding migrations in mid-January to early March of 2013 and 2014. The relationship between body mass changes and explanatory factors including sex, duration of stay at wetland, and distance between site entrance and exit were examined using a set of candidate linear mixed models selected a priori and compared using Akaike's information criterion. Female salamanders lost a greater percentage of body mass during the time in the wetland than males as a result of oviposition. Model selection identified duration of stay as the most important predictor of female body mass change with greater duration of stay associated with lower mass loss. In males, percentage mass loss was most closely associated with site entranceÀexit correspondence with greater distance between entrance and exit sites associated with greater mass loss. These data demonstrate both the importance of wetland entranceÀexit sites and duration of stay at the wetland in determining mass change during spotted salamander reproduction and also that these relationships can differ as a function of sex. Taken together, our findings provide a potential link between behavior, life-history cycles, and costs experienced during reproduction.