Evidence of thermal adaptation in a widely distributed mosquito species

Whether mosquitoes can adapt apace with rapid climate warming will have a large impact on their future distributions, and consequently those of mosquito-borne diseases, but remains unknown for most species. We investigated the adaptive potential of a wide-ranging mosquito species, Aedes sierrensis, by conducting a common garden experiment measuring mosquito fitness and its component life history traits. Although field-collected populations originated from vastly different thermal environments that spanned over 1,200 km, we found that populations varied in maximum fitness, but not in the thermal performance of fitness, with upper thermal limits varying by <1°C across the species range. However, for one life history trait - pupal development rate - we found clear evidence of local thermal adaptation. The upper thermal limits of pupal development rate varied between populations by 1.6°C - five times greater than the average variation in ectotherm upper limits across the same latitudinal extent - and was significantly associated with source temperatures. Despite this evidence of local thermal adaptation, we found that for all populations, temperatures in the source environment already frequently exceed their estimated upper thermal limits, suggesting high vulnerability to additional warming. This was particularly true at the adult life stage, which had the lowest upper thermal limits across traits (31.6°C), the largest impact on mosquito fitness, and occurs during the warmest part of the year. Our results suggest that evolutionary adaptation alone may be insufficient to sustain mosquito populations, and that behavioral thermoregulation and temporary coping strategies are likely important for mosquito persistence under ongoing climate warming. ### Competing Interest Statement The authors have declared no competing interest.