Community-wide seasonal shifts in thermal tolerances of mosquitoes

The broadening in species' thermal tolerance limits and breadth from tropical to temperate latitudes is proposed to reflect spatial gradients in temperature seasonality, but the importance of seasonal shifts in thermal tolerances within and across locations is much less appreciated. We performed thermal assays to examine the maximum and minimum critical temperatures (CTmax and CTmin, respectively) of a mosquito community across their active seasons. Mosquito CTmin tracked seasonal shifts in temperature, whereas CTmax tracked a countergradient pattern with lowest heat tolerances in summer. Mosquito thermal breadth decreased from spring to summer and then increased from summer to autumn. We show a temporal dichotomy in thermal tolerances with thermal breadths of temperate organisms in summer reflecting those of the tropics (tropicalization) that is sandwiched between a spring and autumn temperatization. Therefore, our tolerance patterns at a single temperate latitude recapitulate classical patterns across latitude. These findings highlight the need to understand the temporal and spatial components of thermotolerance variation better, including plasticity and rapid seasonal selection, and the potential for this variation to affect species responses to climate change. With summers becoming longer and increasing winter nighttime temperatures, we expect increasing tropicalization of species thermal tolerances in both space and time.

Automated summary

The study demonstrates that thermal tolerances of mosquito communities change with seasonal shifts in temperature, with lowest heat tolerances in summer. The temporal dichotomy in thermal tolerances shows temperate organisms' thermal breadths reflecting those of tropical regions, sandwiched between temperate and tropical conditions in spring and autumn. As summers lengthen and winter nighttime temperatures increase, species' thermal tolerances are expected to become more tropicalized in both space and time.