Carbohydrate-rich diet increases critical thermal maximum in ants

To understand species' responses to climate change, we must better comprehend the factors shaping physiological critical thermal limits. One factor of potential importance is nutrient availability. Carbohydrates are an energy source that can directly affect an organism's physiological state. Ants are among the most omnipresent and ecologically relevant animal groups on Earth, and many ant species consume carbohydrate-based diets. Additionally, as ectotherms, ants are highly vulnerable to the effects of climate change. Here, we examined the relationship between foraging temperature, carbohydrate availability, and critical thermal maximum (CTmax) in ants (Hymenoptera: Formicidae). First, we conducted a laboratory experiment using 3-4 colonies of two species that forage at high temperatures (Camponotus blandus Smith and Dorymyrmex thoracicus Gallardo) and two species that forage at lower temperatures (Nylanderia fulva Mayr and Dolichoderus quadridenticulatus Roger). Each colony was divided into two experimental subcolonies, which were given diets containing different carbohydrate concentrations (5 vs. 20% sucrose solutions). We then measured CTmax. We also collected ants belonging to these species in the field and measured their CTmax. We found that CTmax was highest for the two species that forage at higher temperatures. For C. blandus and D. thoracicus, workers given 20% sucrose had higher CTmax than workers given 5% sucrose. No diet-mediated differences in CTmax were seen for N. fulva and D. quadridenticulatus workers. Additionally, the experimental ants in both treatment groups had higher CTmax than their field-collected conspecifics, except in the case of C. blandus. If carbohydrate-rich diets can boost heat tolerance in some species, it is possible that changes in resource availability could determine how climate change affects ants, especially species with carbohydrate-based diets. Furthermore, these impacts could ripple across the entire trophic network.