The impact of heatwaves on the behaviour of the Madascar hissing cockroach

The impacts of climate change are increasingly evident across ecosystem, affecting humans, animals and plants. A major consequence of climate change is the increase in the frequency and intensity of extreme events, particularly hot days and heatwaves, defined as short periods of unusually high temperatures. While research has largely focused on survival, other traits, particularly behavioural and reproductive ones, often provide more sensitive indicators of species’ vulnerability. These aspects, especially in relation to social and explorative behaviours, remain poorly understood. This thesis addresses this knowledge gap by investigating how heatwaves affect key traits across multiple biological levels. A combination of laboratory experiments, semi-natural field studies, chemical analyses, and a comparative meta-analysis of invertebrate studies was used to assess the interplay between heatwaves and behavioural traits. Empirical work has focused on two tropical insect species, the Madagascar hissing cockroaches Gromphadorhina portentosa and Elliptorhina chopardi. Across studies, three main patterns emerged. First, behavioural traits were consistently more sensitive than morphological ones. Second, heatwaves increased inter-individual variability revealing differential effects to heat stress. Third, sociality buffers individuals against thermal stress while itself being influenced by social conditions. Behavioural traits, such as boldness, exploration, and aggression, were strongly affected, heatwaves increased variability among individuals and disrupted social hierarchies, while group-living provided buffering benefits, stabilising behaviour and reducing mortality. Chemical analyses further revealed that cuticular hydrocarbon profiles, critical for desiccation resistance and social communication, were shaped by both heat stress and social environment, with potential downstream effects on reproduction and social living. This thesis shows how heatwaves challenge body condition, exploration, social interactions, and survival of animals. These findings emphasise the ecological relevance of sublethal effects and behavioural plasticity, providing critical insights into how organisms may cope with increasing frequency and intensity of heatwaves under climate change.