Costs and benefits of heat and cold hardening in a soil arthropod

Thermal plasticity can increase thermal limits and may be of central importance to the ability of species to cope with future climatic changes. However, little is known about the costs and benefits of plastic responses of ectotherms and for soil species in particular. Here, we examine the costs and benefits [measured as critical thermal minimum and maximum (CTmin and CTmax, respectively)] of duration of heat and cold hardening and its reversal in the soil arthropod Orchesella cincta. Furthermore, we examine the effect of rate of temperature change and age of tested individuals. Increasing rates of temperature change increased CTmin and CTmax, whereas age had a significant effect only on CTmax. There was a strong increase in CTmin and decrease in CTmax with duration of cold hardening and vice versa for heat hardening. The time course of re-acclimation to 20 degrees C after exposure to 4 degrees C for 2 h showed an initial decrease in CTmin, but this effect was gone after 96 h. Re-acclimation to 20 degrees C after exposure to 33.4 degrees C for 2 h showed an initial increase in CTmax and CTmin and these costs and benefits were gone after 96 h. These results add to our understanding of the costs and benefits of hardening and its reversal in soil organisms.