Heat water and reptiles – do the hydro‐thermal properties of animals at the source location persist at the translocation site?

Assisted colonization to locations predicted to remain climatically suitable in the future is increasingly necessary to mitigate climate change effects in ectotherms such as reptiles. However, these future‐suitable locations are often currently cooler than those from which individuals are sourced. While species‐wide paradigms prevail, responses to thermal regimes may vary across a species range, affecting daily activity, colonization and survival in a new environment. Additionally, hydro‐regulatory behaviours are severely understudied, despite the need for understanding trade‐offs between thermoregulation and hydro‐regulation for successful assisted colonization strategies. We investigated behavioural responses to temperature and relative humidity in two latitudinally distinct lineages of pygmy bluetongue (Tiliqua adelaidensis), a cryptic, burrow‐dwelling endangered lizard, in the Mid‐North of South Australia. From spring 2020 to autumn 2021 we took monthly field‐based approach distance and behavioural footage at the source locations and at a southerly translocation site. Behaviours were matched to site‐specific microclimate data prior to principal component and generalized linear mixed model analysis. We found lineage differences in behaviour that persisted after translocation; southern lineage lizards showed significantly less daily activity and were active at lower temperatures and higher humidity than northern lineage lizards. Southern lineage lizards allowed a human observer to approach closer as base‐of‐burrow humidity increased, while northern lineage lizards were quicker to retreat into burrows, at both source and translocation sites. Novel, non‐invasive field‐based activity curves successfully identified lineage differences in humidity and temperature ranges for surface activity, implying environmental preferences of target populations that were reinforced by the models. Specifically, we found evidence for thermoregulation and adaptation/acclimation to higher temperatures in northern lizards and hydroregulation and adaptation/acclimation to cooler, more humid conditions in southern lizards. The limited behavioural plasticity shown by translocated individuals over the season demonstrates the importance of understanding lineage‐level behaviours, hydro‐regulation, and micro‐climate when selecting individuals for assisted colonization.