Nest-site philopatry and the evolution of temperature-dependent sex determination

Despite intensive research, there is no clear empirical evidence to explain the evolution and persistence of temperature-dependent sex determination i n reptiles. A recent hypothesis presented by Reinhold proposes that natal h oming could lead directly to the evolution of temperature-dependent sex det ermination. According to his hypothesis, daughters are produced in rare hig h-quality sites (associated with higher survival rates) to which they retur n and use to nest, thus deriving higher fitness than sons for whom the qual ity of the natal patch does not affect their reproductive output if they su rvive to maturity. We performed an initial empirical evaluation of several assumptions and predictions of this hypothesis as applied to painted turtle s (Chrysemys picta), using data from five consecutive nesting seasons, on a major nesting beach. Females were somewhat philopatric to microgeographic sites and to vegetation cover types within the nesting beach, consistent wi th one of the assumptions of Reinhold's hypothesis. The variables we examin ed that influence hatchling fitness (predation, hatching success and sex ra tio) were not stable at microgeographic nesting sites or at vegetation cove r types. Predation was repeatable within females, whereas hatching success and sex ratio were not. Contrary to Reinhold's hypothesis, females did not nest more frequently in open sites (which tend to produce more females) tha n in patches with more vegetation (which tend to produce more males). Furth ermore, preferred nest sites (as measured by nest density) did not produce predominantly females. However, nests with higher hatching success tended t o produce slightly more females (although the magnitude of this effect was very small). Therefore, Reinhold's hypothesis is not applicable to C. picta at the level studied - that is, within a nesting beach over a 5 year perio d - because most of the essential conditions were not met by our data.