INCUBATION-TEMPERATURE INFLUENCES SEX AND HATCHLING SIZE IN THE NEOTROPICAL TURTLE PODOCNEMIS-UNIFILIS

Influence of incubation temperature on sex determination, hatchling size, and residual yolk in Podocnemis unifilis were studied under natural and laboratory conditions. Nest temperatures and sex ratio were influenced by the sand texture of the nesting site. Switch experiments performed in the field revealed that the critical period is longer and covers more developmental stages than in other species of turtles developing under constant conditions. Mean and variance in incubation temperature and number of hours at or above the threshold temperature were the indices Chat best described sex ratio in nature. Hatchlings were heavier when incubated in nests with higher mean temperatures. Residual yolk weight was positively related to egg width.