Effects of incubation temperature on embryonic development and sex determination in the north African Agamid Lizard, Agama impalearis

The effects of temperature on incubation time, embryo survival, sex ratio, embryo growth and size at hatching were investigated in the north African A gamid lizard, Agama impalearis. Seven constant temperature treatments (span ning 20-36 degreesC) were employed and a split clutch design was used to as sign eggs from the same clutch to the different treatments. Incubation time varied significantly with temperature treatments. Embryos incubated at 32 degreesC, 34 degreesC and 36 degreesC hatched between 41 and 46 days, where as embryos incubated at 26 degreesC and 28 degreesC hatched at 83 and 67 da ys respectively. Hatching success was higher at 28 degreesC, 30 degreesC, 3 2 degreesC and 34 degreesC, but much lower at 26 degreesC and 36 degreesC; hatching did not occur at 20 degreesC. Eggs incubated at 26 degreesC and 36 degreesC produced only females. At 28 degreesC, 30 degreesC, 32 degreesC a nd 34 degreesC, the percentages of males were 9%, 53.5%, 32%, and 58% respe ctively. These sex ratios can be explained by a temperature-dependent mecha nism of sex determination. The relative growth rates are highest early in i ncubation and lower for several days prior to hatching. The relationship be tween snout-to-vent length and age of embryos seems to be best described by a polynomial fitted regression. Growth rates at 26 degreesC were much lowe r than those at 34 degreesC. Constant incubation temperatures affected both snout-to-vent length and body mass at hatching, with maximum body size occ urring at intermediate constant incubation temperatures (30 degreesC, 32 de greesC and 28 degreesC). According to this study, the optimal temperatures of embryonic development probably lies within the range 28-34 degreesC. The possible adaptive significance of incubation temperature effects on some l ife history characteristics of A. impalearis is discussed.