Significant colony differences in thermal tolerances and decoupling of high and low critical temperatures in the army ant Eciton burchellii parvispinum

Differences in behaviour and physiology among social insect colonies provide opportunities for evolutionary responses to environmental selection. Colony differences in thermal physiology can indicate potential for social insect populations to accommodate temperature extremes and determine how populations will respond to changing climates.We tested whether army ant (Eciton burchellii parvispinum) colonies differed in their distributions of worker tolerances of extreme low temperatures (CTmin) and extreme high temperatures (CTmax). We sampled workers across a range of body sizes in each colony, and we collected data from colonies at both warmer low elevation sites and cooler high elevation sites.Colonies differed significantly in the distributions of both CTmin and CTmax; colony mean CTmin and CTmax were not correlated.The colony differences were not associated with worker body size variation. Some thermal physiology differences were associated with local climates: colonies from warmer lower elevation sites had significantly higher CTmin and higher CTmax, but much of the inter-colony variation was unexplained.If significant colony variation in thermal physiology is associated with genetic differences, thermal environments could drive evolutionary changes in thermal physiology.