Shifts in thermal tolerance of the invasive Asian house gecko (Hemidactylus frenatus) across native and introduced ranges.
The ability to rapidly adjust thermal tolerance in response to variable temperatures may facilitate the success of invasive species in non-native ranges. The Asian house gecko Hemidactylus frenatus is native to the tropics of South and Southeast Asia. This small lizard has spread across the globe and has also successfully invaded colder regions of Australia. In this study, we investigated whether this species displays plasticity in thermal tolerance in its introduced range. We measured cold tolerance (CTmin) and heat tolerance (CTmax) of H. frenatus from two native tropical populations in Thailand, and two introduced subtropical populations in southeastern Australia. We also explored seasonal variation in the thermal tolerance of the introduced populations. We found that heat tolerance (CTmax) of geckos did not differ among four populations in Thailand and Australia (range = 43.4-43.7°C). By contrast, geckos from southeastern Australia had lower cold tolerance (CTmin) (mean = 10.43°C) than geckos from Thailand (mean = 11.57°C). We also documented seasonal shifts in cold tolerance of H. frenatus from southeastern Australia. Geckos captured in winter had cold tolerances 1-2°C lower than those captured in summer. Unexpectedly, this shift in cold tolerance was accompanied by a 1-2°C upward shift in heat tolerance. Our results support a growing body of evidence showing that tropical invaders can adjust cold tolerance downwards via plasticity or acclimation. Such changes may allow tropical invaders to expand their geographic range into colder regions of non-native ranges.