Thermal stress impairs survival and immune responses in ant founding queens.

Rising temperatures associated with global warming affect all organisms, particularly ectotherms such as insects. Ant queens provide an ideal model for studying the effects of thermal stress because of their distinctive life-history traits. After mating, nest-founding queens of many species undergo a critical phase in which they search alone for a suitable site to establish a new colony. Despite growing concern about the effects of thermal stress on organisms, we still lack detailed understanding of how heat intensity and exposure duration influence mortality and immune function in founding queens, both of which are key to successful colony establishment. Here, we tested how these factors affect mortality and encapsulation, a proxy for immune response in insects, in queens of the common garden ant Lasius niger during colony founding. We found that heat stress increased queen mortality, regardless of exposure duration to heat, and decreased their encapsulation responses, indicating compromised immune function. These results highlight the detrimental effects of high temperatures on ants, organisms that provide essential ecological services.