Thermal tolerance of monomorphic ants: The importance of body size

Abstract

The foraging behavior of ants may be linked to the body size of workers, which serves as an adaptation to suboptimal external temperatures. The relationship between foraging behavior and body size is especially noticeable in polymorphic species, which display a broad range of variation in worker body size. An increasing number of studies have found that body size plays an important role in the division of labor among monomorphic ants, which do not display physical subcastes of workers. This study aimed to investigate whether the workers of the monomorphic ant Lasius niger respond to temperature in a similar way to polymorphic species. Surprisingly, our findings indicate that the mean body size of workers foraging in high temperatures during the afternoon is significantly smaller than that of workers foraging in much lower temperatures during the morning. Our study supports the idea, proposed by other authors, that simple radiative heat transfer does not fully explain the significance of body size for thermal tolerance. We hypothesize that allocating smaller workers when the temperature is high protects the colony from overheating.