Temporal plasticity of thermal tolerance in ants

How do individuals tolerate both hot and cold climates of our planet? One possibility is that organisms have plastic traits, such as thermal tolerance, that allow them to function in highly variable environments. In this study, we tested whether phenotypic plasticity of temperature tolerance (i.e., acclimatization in the field and acclimation in the lab) occurs in the red harvester ant, Pogonomyrmex barbatus, at two temporal scales. We first measured the upper and lower critical thermal limits (CT_max and CT_min) of ants monthly for 2 years while concurrently measuring environmental conditions. Both CT_max and CT_min covaried with temperature in a predictable way; values increased in a positive, linear manner. We then experimentally tested whether CT_max and CT_min could shift within a shorter time period by exposing subcolonies of ants to cool (10°C), moderate (20°C), and hot (30°C) temperatures for 10 days. CT_max increased only slightly at the hottest temperature treatment (+1.2°C); however, CT_min increased considerably under both moderate (+2.6°C) and hot treatments (+3.8°C). Combined, our results suggest that the thermal tolerance of ants may be more plastic than originally hypothesized, potentially aiding an already thermophilic clade in future climate scenarios.