Cold resistance depends on acclimation and behavioral caste in a temperate ant
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Adjusting to low temperatures is important for animals living in cold environments. We studied the chill–coma recovery time in temperate ant workers (Temnothorax nylanderi) from colonies collected in autumn and spring in Germany. We experimentally acclimated these ant colonies to cold temperatures followed by warm temperatures. As expected, cold-acclimated workers recovered faster from freezing temperatures, but subsequent heat acclimation did not change the short recovery times observed after cold acclimation. Hence, either heat acclimation improves cold tolerance, possibly as a general response to stress, or at least it does not negate enhanced cold tolerance following cold acclimation. Colonies collected in spring showed similar cold tolerance levels to cold-acclimated colonies in the laboratory. Next, we compared the chill–coma recovery time of different worker castes and found that exterior workers recovered faster than interior workers. This difference may be related to their more frequent exposure to cold, higher activity level, or distinct physiology. Interior workers were also heavier and showed a higher gaster-to-head ratio and thorax ratio compared to exterior workers. An obvious difference between exterior and interior workers is activity level, but we found no link between activity and cold tolerance. This suggests that physiology rather than behavioral differences could cause the increased cold tolerance of exterior workers. Our study reveals the importance of acclimation for cold tolerance under natural and standardized conditions and demonstrates differences in cold tolerance and body dimensions in monomorphic behavioral castes of an ant.
KeywordsBehavioral castes Cross-protection effect Hardening Intranidal workers Social insects
We are grateful to Ilka Kureck and Barbara Feldmeyer for their comments on a previous version of the manuscript. We thank also Stefanie Emmling, Marion Kever, and Heike Stypa for their help in the laboratory. I.S. is grateful to the Minerva Stiftung for supporting his postdoctoral research. A.P.M. and T.P. were funded by a Deutsche Forschungsgemeinschaft grant to S.F. (DFG Fo 298/11 and 298/9).
Movie 1: Recovery process from chill coma of a Temnothorax nylanderi worker. The worker ant was placed in -20˚C for 4 minutes and the few seconds of its recovery were filmed. Recovery time varied based on acclimation and behavioral caste, but the recovery process itself was similar for all workers. (MPG 4337 kb)
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