South Dakota State University Brookings, South Dakota
How do individuals tolerate both the hot and the cold climates of our planet? One possibility is that traits like thermal tolerance, which allow organisms to function in highly variable environments, are plastic. Thermal tolerance (i.e. the range of temperatures at which an organism can survive) has been quantified for many species, yet the extent of trait variation and its potential correlates remain uncertain. Here we test if thermal tolerance is a plastic trait in the red harvester ant, Pogonomyrmex barbatus. To do this we measured the lower and upper critical thermal limits (CTmin and CTmax) of worker ants each month for two years while concurrently measuring temperature at regular intervals. Across months, both CTmin and CTmax co-varied with temperature in a predictable way; values increased in a positive, linear manner. We also questioned whether ant thermal tolerance could shift to accommodate temperature variability at shorter time scales (i.e. within a month). To test this, we placed sub-colonies of ants into environmental chambers set at 10, 20, and 30°C. We monitored ants for 10 days and then ran thermal assays as before to compare our results to both initial field collections and treatment differences. CTmin increased considerably with treatment temperature, however, CTmax was not different from the initial field collection. Combined, our results suggest that thermal tolerance of ants may be more plastic than originally hypothesized, potentially aiding an already thermophilic clade of ectotherms under future climate scenarios.
