Thermal benefits of polygyny? Multi-queen desert ant colonies have higher and more uniform heat tolerance

Investigations of thermally adaptive behavioral phenotypes are critical for predicting global species distributions under climate change conditions. However, this remains a relatively understudied area of macrophysiology. The interplay between cooperative behavior and group thermal performance in particular is paramount to understanding current and future distributions of highly social insects, which comprise some of the most abundant and ecologically important animal species on earth. We examined the effects of alternative social strategies on thermal tolerance in a facultatively polygynous (multi-queen) desert ant, Pogonomyrmex californicus. Polygyny, a common strategy in harsh environments, can enhance colony growth and competitive advantage, but the mechanisms behind these advantages are not well known. We asked whether and how queen number affects worker thermal tolerances. We established and reared colonies with 1 to 4 queens, then quantified worker heat tolerances (CT_max). Colonies with more queens had higher and less variant CT_max. These findings resemble “weak link” patterns, in which colony group thermal performance is improved by reducing frequencies of the most temperature-vulnerable individual phenotypes. We also characterized summer diurnal temperatures in this species’ native range. Our findings suggest that multi-queen colonies have thermal tolerance distributions that enable increased mid-day foraging where they naturally occur. These insights help explain the success of polygyny in hot environments, including cities and deserts, and suggest advantages to polygyny under climate change scenarios.