The effects of incubation environment, sex and pedigree on the hatchling phenotype in a natural population of loggerhead turtles

Explaining environmental sex determination (when offspring sex is determined by a property of the embryonic environment) in reptiles remains one of the greatest problems in the field of sex allocation. We test Charnov and Bull’s differential fitness hypothesis in a natural population of loggerhead sea turtles in the field. This hypothesis states that the embryonic environment affects a trait that has different fitness consequences for males and females. We experimentally manipulated the incubation environment experienced by each sex and measured the phenotypic variation observed in hatchlings from experimental clutches and additional natural nests. Sand temperature had a negative correlation and percent water content had a positive correlation on the size of hatchlings from natural nests, and there was a significant interaction between sex and sand temperature on mass. This suggests that females, who develop in warm temperatures, are larger than males at hatching. The Charnov and Bull hypothesis would explain this pattern of environmental sex determination if larger size at hatching leads to a greater increase in lifetime fitness for females than males.