Abstract

In a world wherein climate is rapidly changing, understanding species’ adaptations to climate is crucial. Quantifying phenotypic variation occurring across the range of a species is a useful approach to infer how populations adapt or show plastic responses to climatic regimes. In understudied groups such as eusocial ant colonies, the degree of worker polymorphism, whereby workers vary in size and scaling, is a phenotypic trait of the “superorganism”. Yet, the degree to which such variation changes plastically or evolves in response to geographic variation in environmental factors remains poorly explored. Here, I first test whether the degree of variation in worker polymorphism in colonies of the carpenter ant Camponotus herculeanus varies predictably along a broad-scale latitudinal gradient and then examine the environmental factors driving this phenotypic variation. I found that the proportion of major workers within a colony decreased with increasing latitudes and was most related to regional climate. However, contrary to my expectation, variation in mean major worker body size did not correlate with worker polymorphism and was most related to colony size. These results suggest that change in the social phenotype of the superorganism is a plastic response to cooler and shorter seasons typical of northern latitudes, rather than resulting from the evolution of new developmental thresholds. I conclude that elucidating how genes and development interact to shape phenotypes along environmental gradients is key to improving understanding and predictions of climate adaptations in social organisms.