Assessment of patterns of temperature-dependent sex determination using maximum likelihood model selection

Sex determination in some reptiles is independent of egg incubation temperature and is called genotypic sex determination (GSD). In many other reptiles, sexual phenotype is dependent on incubation temperature. This phenomenon is called temperature-dependent sex determination (TSD). TSD is categorized by three patterns, based on the majority sex produced at lower and higher incubation temperatures, named MF for Male-Female, FM for Female-Male, or FMF for Female-Male-Female. When large numbers of eggs are incubated at many different incubation temperatures, the assessment of TSD pattern is unambiguous, but when few eggs or few incubation temperatures are used, the categorization of TSD pattern is less straightforward. We propose a new methodology based on maximum likelihood model selection that evaluates and ranks the performance of four descriptive models of sex determination for discrete datasets. This method has the added benefit of giving standardized definitions of two commonly reported parameters of TSD: the pivotal temperature and the transitional range of temperature. Standardization of analyses will help facilitate cross-species meta-analyses of TSD in reptiles.