Temperature-dependent sex determination in the Nile crocodile, Crocodylus niloticus, in the Okavango River, Botswana, and the effect of global climate change

[摘要] ENGLISH ABSTRACT: The Nile crocodile, Crocodylus niloticus exhibits temperature-dependent sexdetermination, where sex is determined by the incubation temperature of the egg prior tohatching. Laboratory incubation of the eggs indicated that the lower and upper pivotaltemperature for the Nile crocodile in the Okavango River, Botswana was 31.4°C and33.4°C respectively. Exclusively females were produced at a constant temperature of30.0°C, 30.5°C and 34.0°C, 71% females were produced at 31.0°C and the majoritymales were produced at 31.5; 32.0; 32.5 and 33.0°C. Crocodylus niloticus in theOkavango Region therefore has a female-male-female pattern of temperaturedependentsex determination where females are produced at lower and higherincubation temperatures. Embryonic development, incubation period, hatching successand development rates were strongly temperature dependent. The location of nestsplays an important role in determination of incubation temperature. At a distance of 6mfrom the river, soil temperature was at a maximum at a depth of 25cm. Breeding femaleschoose nesting sites based on optimal soil temperatures. Along the Okavango River theaverage nest sites were 5.6m from the river, and the eggs were at an average depth of24.5cm. Calculation of mean nest temperature during the thermosensitive period (sexdetermining period) of incubation for ten wild Nile crocodile nests indicated that thenests along the Okavango River are primarily female-biased. An increase in average airtemperature due to Global Climate Change could possibly shift the population to a malebiasedsex ratio, leading to eventual extinction of the Nile crocodile in the OkavangoRiver.Stellenbosch University https://scholar.sun.ac.za

[发布机构] Stellenbosch University