Our understanding of range shifts in response to climate change principally hinge on distribution modeling based on the contemporary distributions of organisms. Many plants and animals may have the physiological capacity to live in hotter and more variable environments, and understanding how animal behaviorally adjust to hotter conditions is critical for modeling future species distributions and community assembly processes. Many of these processes hinge on fine-scale changes in thermal conditions that typically overlooked.
Social insects often adapt to environmental conditions by altering the division of labor among workers in the colony. When colonies experience thermal stress, how is it that the expression of heat tolerance varies among workers? Is it possible that colonies are capable of adapting to thermal challenges by allocating resources to workers that specialize on heat tolerance to forage during hot conditions? Is it possible that colonies have a capacity for greater heat tolerance that cannot be assayed by measuring the performance of individual workers? We designed a set of experiments to thermally challenge colonies of thieving ants (Ectatomma ruidum) in the laboratory to assay temporal variation and intracolonial variation in the capacity to persist in thermally changing foraging conditions. This was coupled with a set of field observations and marking of individuals foraging at different thermal conditions. We tested whether there workers specialize with respect to thermal persistence, and whether thermal persistence followed a circadian rhythm, and whether colonies can modify their capacity for thermal persistence after experiencing more challenging thermal environments.
Results/Conclusions
We found that the expression of thermal persistence followed a diel cycle, suggesting that the expression of heat shock proteins follows an endogenous circadian rhythm. We found that individuals that were observed foraging under hot conditions in the field expressed a higher thermal persistence than individuals who were not foraging under those conditions, even at time points several days beyond that foraging episode. This suggests that there is interindividual variation and specialization with respect to thermal persistence. We also found that chronic application of thermal challenges to whole colonies resulted in increased thermal persistence of individual workers relative to controls, suggesting that colonies might have a greater capacity to respond to changing thermal environments than predicted by classic species distribution modeling. We conclude that the behavior of individuals in the context of microgeographic variation, and understanding the flexibility of behavior in colonial organisms, are important for interpreting and predicting responses to climate change.