Temperature-Dependent Sex Determination in Crocodilians and Climate Challenges

Abstract

The sex of crocodilians is determined by the temperature to which the eggs, and hence the developing embryo are exposed during critical periods of development. Temperature-dependent sex determination is a process that occurs in all crocodilians and numerous other reptile taxa. The study of artificial incubation temperatures in different species of crocodiles and alligators has determined the specific temperature ranges that result in altered sex ratios. It has also revealed the precise temperature thresholds at which an equal number of males and females are generated, as well as the specific developmental period during which the sex of the hatchlings may be shifted. This review will examine the molecular basis of the sex-determination mechanism in crocodilians elucidated during recent decades. It will focus on the many patterns and theories associated with this process. Additionally, we will examine the consequences that arise after hatching due to changes in incubation temperatures, as well as the potential benefits and dangers of a changing climate for crocodilians who display sex determination based on temperature.

Keywords: DNA methylation; SF-1; SOX-9; TRPV; anti-Müllerian hormone; aromatase; climate change; crocodile sex determination; miRNA.

Figure 1

TSD2 pattern of A. mississippiensis: Males have a low proportion at decreased and very high temperatures, while at the intermediate temperatures, higher male ratios can be observed (dotted line). The blue and rosa bands describe the development of the PTs where a 50% male proportion was observed at 31.7 °C and 35.9 °C, while at 33.4 °C, the highest male ratio was found, according to the data of González (2019) [13].

Figure 2

Schematic figure for summarizing the involvement of steroid hormones, enzymes, and genes in the TSD mechanisms.