The Effect of Incubation Temperature on Sex and Morphology in the African Redhead Agama (Agama picticauda)

Abstract

The first demonstration of temperature-dependent sex determination (TSD) in a vertebrate was in the African redhead agama (Agama agama) nearly 50 years ago. The original study was generally overlooked until it was later identified in turtles, which attracted more interest into this peculiar sex determining mechanism. Since then, numerous studies have investigated the physiological mechanisms behind TSD, the evolutionary transitions between genetic sex determination and TSD, and the adaptive significance of TSD, however, research on the original species has not been conducted. My research aims to revisit the original study to evaluate the effect of incubation temperature on sex ratio and fitness-relevant phenotypes, and to identify the sex-specific effects of incubation temperature in Agama picticauda (formerly A. agama). Eggs were incubated under constant and ecologically-relevant fluctuating temperatures to better characterize the pattern of TSD in this species, provide insight into the ecological relevance of TSD, and quantify the effects of incubation temperature on fitness-relevant phenotypes and sex-specific effects. Hatchling sex ratios varied with incubation temperature in a pattern similar to a female-male-female pattern of TSD. Fitness-relevant phenotypes were also affected by incubation temperature, although the effects were not sex-specific. Eggs incubated at male-biased temperatures hatched earlier than eggs at female-biased temperatures, which may have sex-specific consequences later in life as predicted by models for the adaptive significance of TSD.