Thermal specialization across large geographical scales predicts the resilience of mangrove crab populations to global warming.

The broad prediction that ectotherms will be more vulnerable to climate change in the tropics than in temperate regions includes assumptions about centre/edge population eff ects that can only be tested by within-species comparisons across wide latitudinal gradients. Here, we investigated the thermal vulnerability of two mangrove crab species, comparing populations at the centre (Kenya) and edge (South Africa) of their distributions. At the same time, we investigated the role of respiratory mode (water- versus air-breathing) in determining the thermal tolerance in amphibious organisms. To do this, we compared the vulnerability to acute temperature fl uctuations of two sympatric species with two diff erent lifestyle adaptations: the free living Perisesarma guttatum and the burrowing Uca urvillei , both pivotal to the ecosystem functioning of mangroves. Th e results revealed the air-breathing U. urvillei to be a thermal generalist with much higher thermal tolerances than P. guttatum . Importantly, however, we found that, while U. urvillei showed little diff erence between edge and centre populations, P. guttatum showed adaptation to local conditions. Equatorial populations had elevated tolerances to acute heat stress and mechanisms of partial thermoregulation, which make them less vulnerable to global warming than temperate conspecifi cs. Th e results reveal both the importance of respiratory mode to thermal tolerance and the unexpected potential for low latitude populations/species to endure a warming climate. Th e results also contribute to a conceptual model on the latitudinal thermal tolerance of these key species. Th is highlights the need for an integrated population-level approach to predict the consequences of climate change.