Match or mismatch: Tokay geckos adjust their behaviour to familiar and unfamiliar handlers but according to the context

Animals need to distinguish among different con- and heterospecific individuals to be able to adjust behaviour appropriately. Behavioural responses towards familiar individuals might vary based on context in which they are encountered. However, such context dependent responses, while beneficial in the wild, can impact experimental results, increase error, decrease reproducibility and threaten scientific advancement. Consequently, it is essential to understand how and when experimenters influence animal behaviour. Here, we tested captive Tokay geckos (Gecko gecko) ability to discriminate familiar and unfamiliar handlers across two situations (novel and routine). In the novel situation, we induced tonic immobility through physical constraint, a protocol the animals had never experienced before. In the routine situation, we fed lizards live prey with tweezers (as during regular husbandry). Geckos behaved differently towards familiar and unfamiliar handlers in a routine situation but not in an novel situation. Nevertheless, we found high individual repeatability in tonic immobility (R = 0.41-0.56). Our study, therefore, has implications for animal behaviour, cognition and welfare, while revealing important insights into context specific responses in relation to handler identity, factors that are rarely considered in experimental animal studies but that can significantly impact results.