Abstract
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 (CTmax) 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 (CTmin) 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 CTmax and 9.9 °C for CTmin) 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.
Highlights
Invasive species are a global environmental problem due to their ability to disrupt native ecosystems and cause declines or extinctions of native species (Lockwood et al 2013)
We investigated whether invasive house geckos from southeastern Australia show differing thermal hardening responses than individuals from the native range in Thailand
Geckos from Thailand were transported to Prince of Songkla University (PSU), while geckos from New South Wales (NSW) were transported to the University of Technology Sydney (UTS)
Summary
Invasive species are a global environmental problem due to their ability to disrupt native ecosystems and cause declines or extinctions of native species (Lockwood et al 2013). The exposure to cold temperatures can generate the upregulation of cold-shock proteins (CSP) (Ritossa 1962; Seebacher 2005; Thieringer et al 1998) or induce metabolic adjustments without additional protein syntheses (Lee et al 1987; Teets and Denlinger 2013; Teets et al 2020), which allow organisms to survive exposure to colder temperatures These rapid responses to thermal stresses should facilitate the survival of introduced species during the transport and early introduction phases of the invasion when they encounter unfamiliar climates (Chown et al 2007; Nyamukondiwa et al 2010). Most studies investigating the thermal hardening responses have focused on dipteran insects (Chown et al 2007; Hu et al 2014; Nyamukondiwa et al 2010)
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