Temperature, phenotype, and the evolution of temperature-dependent sex determination: how do natural incubations compare to laboratory incubations?

Phenotypic variation is a fundamental component of the process of evolution and understanding the factors that create this variation is critical to investigations of this process. We test the hypothesis that phenotypic variation created under natural incubation conditions will differ from that created under constant laboratory conditions in a reptile species with temperature-dependent sex determination (TSD), the red-eared slider turtle (Trachemys scripta). Using a split clutch design, we demonstrate that offspring morphology, behavior, and sex differed between hatchlings incubated in the field and those from the laboratory, but immune response did not. The interactions between different phenotypic parameters will ultimately determine how natural selection acts upon offspring, and consequently our data suggest that offspring developing under these differing conditions should have different fitnesses. The relationship between offspring sex and phenotype serves as the theoretical foundation on which most investigations into the evolution of TSD are built. Thus, it may be necessary to use natural incubation conditions to accurately examine how offspring sex relates to other phenotypic parameters if we are to understand the evolution of this sex determining mechanism. (c) 2009 Wiley-Liss, Inc.