The effects of incubation temperature on locomotor performance, growth and survival in hatchling velvet geckos

The thermal environment that lizard eggs experience during incubation can affect the size, shape and performance of hatchlings. Summer heatwaves are predicted to increase in frequency and duration in the future, and could produce higher temperatures inside lizard nests. Increase in nest temperatures may influence offspring sex, body size, growth and locomotor performance, which in turn can affect fitness. We investigated whether incubation temperatures influenced the locomotor performance of hatchlings of the velvet gecko (Amalosia lesueurii), a nocturnal gecko that lays eggs in communal nests inside rock crevices. We incubated eggs at two fluctuating temperature regimes that mimicked current nest temperatures (mean=23.2 degrees C, range 10-33 degrees C, current') and predicted future nest temperatures (mean=27.0 degrees C, 14-37 degrees C, future'). We measured the locomotor performance of hatchlings at four temperatures (20, 25, 30 and 35 degrees C), and released them at two field sites (Nowra and Dharawal National Park, DNP') to estimate their growth and survival over 10months. Hot-incubated hatchlings were smaller, and ran more slowly than current-incubated hatchlings at all four test temperatures. Incubation temperature did not affect the growth rates of lizards from Nowra, but at DNP, hot-incubated lizards grew more slowly than current-incubated lizards. Survival analyses revealed that future-incubated hatchlings had lower survival than current-incubation hatchlings over 10months of life, but selection on hatchling traits differed between study sites. For hatchlings from DNP, there was evidence for directional selection on body mass, but little support for selection on SVL or speed. At Nowra, there was equivalent evidence for selection on mass, SVL and speed. These results demonstrate that incubation induced differences in morphology and locomotor performance can influence the survival of hatchlings. In the absence of maternal plasticity in nesting behavior, future increase in nest temperatures, by altering offspring morphology, performance and survival, have the potential to influence the viability of gecko populations