Softening and Cross-Susceptibility: Exposure to Heat and Desiccation Reduces Future Stress Tolerance in an Insect

The frequency and duration of environmental stressors, such as heat waves and drought, will continue to grow due to ongoing climate change, thereby increasing the likelihood that organisms will experience stressors consecutively. Exposure to one stressor can improve or impair future tolerance to the same stressor (i.e., hardening or softening, respectively), or enhance or reduce future tolerance to a different stressor (i.e., cross-protection or cross-susceptibility, respectively). Understanding whether stress improves or impairs animals' abilities to withstand future stressors is critical for determining the physiological sensitivity of animals to ongoing climate change. Here, we used a factorial design with the variable field cricket (Gryllus lineaticeps) to evaluate whether prior heat or desiccation stress influenced subsequent heat or dessication tolerance. Given the potential energetic costs of hardening and cross-protection, we further examined whether resource (food) acquisition promoted hardening and cross-susceptibility. Prior heat exposure reduced future heat tolerance (i.e., softening), and prior exposure to both heat and desiccation reduced future desiccation tolerance (i.e., softening and cross-susceptibility), potentially due to terminal reproductive investment. Further, resource acquisition (amount of body mass gained) did not influence stress tolerance because individuals that acquired more resources were not more likely to exhibit benefits (rather than costs) to their future stress tolerance. In sum, our results suggest the increasing frequency of climate-related stressors may pose a significant physiological risk to some animals.