Sex in crocodilians is not determined by chromosomes, but by egg incubation temperature, where different temperatures produce different clutch sex ratios. Two patterns have been proposed to describe these changes in sex ratios: a 100% female proportion at low and high temperatures with male predominance at inter- mediate ones (FMF) or a simpler pattern with a single female-to-male transition (FM).
Here, we aimed at gathering the existing data on these patterns to provide models of temperature-dependent sex determination in those crocodilians studied so far.
Potentially relevant publications were searched on Web of Knowledge, Scopus, Scielo and Science Direct. Studies that reported results on the sexual identity of crocodilian hatchlings obtained from constant temperature incubation treatments were considered. Using statistical models varying in their underlying assumptions, we evaluated which sex-determination pattern was best supported for the studied crocodilians and constructed species-specific and latitude-specific models.
Results/Conclusions
Based on the sexual identity of 8,458 hatchlings studied throughout 31 studies, we show that the evidence supports a shared FMF pattern in all the crocodilian species for which enough data are available. We found that such pattern changes between species and at different latitudes, and that asymmetries exist between the transitional ranges of temperature (i.e. those producing mixed clutches), with wider ranges at the MF transition. In general, no single temperature produces male-only clutches, making incubation temperature a poor proxy to sex identity. Finally, we discuss several considerations on the available information on these patterns. Our results suggest a lability of the FMF crocodilian sex-determination pattern, a key feature under the present climate change scenario.