Thermal tolerance differs between co-occurring congeneric beetle species in marine supratidal rockpools

In the context of global change, it is important to know the physiological limits and behavioural responses of species to environmental changes, especially for those living in extreme environments such as supratidal rockpools. Our main study objective was to determine the thermal tolerance of 3 beetle species ( Ochthebius quadricollis, O. subinteger and O. lejolisii ) co-occurring on the western Mediterranean coast using physiological and behavioural thermoregulatory responses to predict their sensitivity to climate change. To this end, we: (1) compared the heat coma (HC) among species and populations; (2) explored the effect of salinity on HC in adults and larvae of O. quadricollis and O. lejolisii ; and (3) determined the temperature thresholds for avoidance responses (water emersion and flight) of adult stages against heat and salinity stressors. We found significant interspecific and interpopulation differences in HC. O. quadricollis larvae and adults were the most heat tolerant, showing similar HC values under different salinity conditions. In O. lejolisii , high salinity (90 g l -1 ) conferred greater thermal tolerance in larvae but lower tolerance in adults. The temperature thresholds for avoidance responses were generally lower than 40°C, but interspecific variation followed their obtained HC patterns. In both of these species, salinity affected the sublethal temperature thresholds for water emersion. An additive effect of temperature and salinity was observed for the frequency of emergence and flight in both species. Our results provide relevant information for estimating thermal safety margins and developing mechanistic predictive models for the survival of these species when faced with current and future climate change scenarios.