Plasticity in thermal hardening of the invasive Asian house gecko.

The Asian house gecko (Hemidactylus frenatus) is a tropical invasive species that has established and spread throughout several temperate regions around the world. In some invasive species, rapid thermal acclimation (thermal hardening) may contribute to their success in occupying a wide range of climates. In this study, we investigated whether invasive house geckos from southeastern Australia show differing thermal hardening responses than individuals from the native range in Thailand. In the laboratory, we measured the basal heat tolerance (CT_max) of the geckos and their heat hardening response after being subjected to the second thermal stress after 1, 3, 5, 7, 9, or 11 h. When geckos had recovered, we measured their basal cold tolerance (CT_min) and cold hardening response over the same time intervals. We then explored whether hardening responses differed between populations or among time intervals. We found that basal heat tolerances did not differ between populations, but geckos from Australia had lower cold tolerance than geckos from Thailand. The magnitude of the heat hardening was similar between populations, but the introduced geckos had a higher magnitude of cold hardening. The native geckos could maximize their cold tolerance capacity for only 0.6 °C, versus 0.9 °C for the introduced geckos. Also, geckos from Australia exhibited faster responses to thermal stress than did geckos from Thailand. Maximum thermal tolerances as a result of hardening responses peaked within three hours after thermal stress in Australian geckos (adjusted means = 44.0 °C for CT_max and 9.9 °C for CT_min) and at five hours after thermal stress in Thailand geckos (adjusted means = 44.2 °C and 10.2 °C, respectively). The plasticity in the thermal hardening of the invasive gecko should enable it to survive rapid temperature fluctuations, especially winter cold snaps that occur in temperate regions. [ABSTRACT FROM AUTHOR]