The Herpetological Journal

pp.101-108

Authors: El Hassan El Mouden , Mohammed Znari And Claude Pieau

Abstract: The effects of temperature on incubation time, embryo survival, sex ratio , embryo growth and size at hatching were investigated in the north African Agamid lizard, Agama impalearis. Seven constant temperature treatments (spanning 20-36°C) were employed and a split clutch design was used to assign eggs from the same clutch to the different treatments. Incubation time varied significantly with temperature treatments. Embryos incubated at 32°C, 34°C and 36°C hatched between 41 and 46 days, whereas embryos incubated at 26°C and 28°C hatched at 83 and 67 days respectively. Hatching success was higher at 28°C, 30°C, 32°C and 34°C, but much lower at 26°C and 36°C; hatching did not occur at 20°C. Eggs incubated at 26°C and 36°C produced only females. At 28°C, 30°C, 32°C and 34°C, the percentages of males were 9%, 53. 5%, 32%, and 58% respectively. These sex ratios can be explained by a temperature-dependent mechanism of sex determination. The relative growth rates are highest early in incubation and lower for several days prior to hatching. The relationship between snout-to-vent length and age of embryos seems to be best described by a polynomial fitted regression. Growth rates at 26°C were much lower than those at 34°C. Constant incubation temperatures affected both snout-to-vent length and body mass at hatching, with maximum body size occurring at intermediate constant incubation temperatures (30°C, 32°C and 28°C). According to this study, the optimal temperatures of embryonic development probably lies within the range 28-34 °C. The possible adaptive significance of incubation temperature effects on some life history characteristics of A. impalearis is discussed.

Keywords: incubation temperature, embryonic development, sex determination, Agama