Effect of variation in incubation temperature and exposure to extreme temperature on the hatchability of Nile crocodile (Crocodylus niloticus) eggs

Abstract

In contrast to older experimental systems which typically incubated eggs at constant temperature, recent wide availability of inexpensive programmable microcontrollers has enabled the development of incubators capable of simulating circadian temperature variation. The present study aimed to compare the effect of two sinusoidally fluctuating temperature regimens (31±3 °C and 31±6 °C) with a constant temperature regimen (31 °C) on egg hatchability of the Nile crocodile, Crocodylus niloticus. Towards the end of the incubation period, an electronic malfunction introduced extreme temperatures (cumulative exposure of eggs to 47 hours of extreme temperatures, with a range of 16.3 to 45.4 °C) which confounded the results. A conditional logistic regression model was used with hatching outcome as the response variable, and incubation regimen and extreme temperature exposure group as the predictor variables. Exposure to extreme temperatures had a severe negative effect on hatchability compared with eggs incubated at a constant temperature of 31 °C (P<0.001). An interesting trend (P=0.12) was that both fluctuating temperature groups had a positive association with hatchability when compared to the constant-temperature group. The hypothesis that fluctuating temperatures may be positively associated with measures of C. niloticus embryo and hatchling health warrants further investigation after addressing the technical challenges identified during the current study.