The influence of the incubation environment and parental care on Tokay gecko (Gekko gecko, Gekkonidae) development in captivity

Birgit Szabo

Parental effects, non-genetic effects that parents exert on their offspring, can result in adaptive phenotypes that ensure offspring survival. In captivity, reptiles often experience unnatural incubation and rearing conditions due to limited nest site choices, which can negatively impact individual development and welfare. Incubation temperature and humidity are especially critical for reptile development, influencing factors such as sex determination, growth, and morphology. However, the conditions experienced after hatching, such as social housing, are far less often considered. Here, I studied the effects of both the incubation environment (temperature and humidity) and social rearing compared to isolation rearing on the development of captive bred tokay geckos (Gekko gecko). I find that both temperature and humidity affect hatchling sex and size but only temperature affected incubation duration. Furthermore, females selected nest sites with higher temperatures. After hatching, rearing group size did not affect Snout vent length or growth, but body condition was higher in offspring raised alone and in smaller family groups compared to larger family groups. My findings confirm temperature dependent sex determination in tokay geckos and a role for humidity in lizard development. Importantly, being raised in larger social groups led to a reduction in body condition across the first six months of life, which was not reflected in SVL alone. My results suggest that despite ample food available, competition within family groups does reduce offspring body condition. Therefore, care should be taken when raising tokay geckos in captivity to provide nest site options and enough food and shelter to ensure optimal development of all offspring.