Pivotal range and thermosensitive period of the pig-nosed turtle, Carettochelys insculpta (Testudines: Carettochelydidae), from northern Australia

Understanding temperature-dependent sex determination in nature often depends on knowledge of species-specific attributes that are integrated into the relationship between temperature and sex. We determined two such attributes for the pig-nosed turtle, Carettochelys insculpta Ramsay, 1886, in tropical Australia: the pivotal range in temperature that separates the male-producing domain from the female-producing domain, and the thermosensitive period during which the embryonic sex is influenced by temperature. The pivotal range for C. insculpta was very narrow, spanning only about 1°C, and was centered on 32°C, which is high but consistent with temperatures reported for other tropical species. The thermosensitive period spanned developmental stages 17-21 for temperature influence in the direction of maleness and 18-21 for temperature influence in the direction of femaleness. This period is slightly narrower than that for other reptile species but broadly consistent with the middle third of incubation.