Cross resistance to environmental stressors in Natal fruit fly, Ceratitis rosa Karsch (Diptera: Tephritidae) and its underlying physiological mechanisms

Abstract

Plastic adjustments of physiological tolerance to a particular stressor can result in fitness benefits for resistance that might manifest not only in that same environment, but might also be advantageous when faced with alternative environmental stressors, a phenomenon termed cross-tolerance. The nature and magnitude of cross-tolerance responses can provide important insights into the underlying genetic architecture, potential constraints on, or versatility of, an organism’s stress responses. The curent study tested for cross-tolerance to a suite of abiotic factors that likely contribute to setting insect population dynamics and geographic range limits: heat, cold, desiccation and starvation resistance in adult mixed sex Ceratitis rosa following acclimation to all of these isolated individual conditions prior to stress assay. Traits of stress resistance measure included critical thermal (activity) limits, chill coma recovery time (CCRT), heat knockdown time (HKDT), desiccation and starvation resistance. In agreement with a range of other studies, we found that acclimation to one stress typically increased resistance for that same stress experienced later in life. A more novel result is that substantial evidence for cross-tolerance was found. For example, we found an improvement in heat tolerance (critical thermal maxima, CTmax) following starvation or desiccation hardening; improved desiccation resistance following cold acclimation, and enhanced starvation resistance following desiccation hardening, indicating pronounced cross tolerance to these environmental stressors for the traits examined. The study further investigated underlying physiological mechanisms to the observed cross tolerance by measuring water balance traits, carbohydrates and lipid content of acclimated and control adult C. rosa. Overlaps in physiological mechanisms such as reduced water loss rates, and high lipid content observed in both heat and starvation treatment C. rosa flies weredetermined to be the likely mechanisms behind the observed increased heat tolerance following desiccation hardening, and improved heat tolerance following starvation acclimation respectively. However physiological mechanisms were not exhaustive hence there is need to conduct further research to explain all observed cross tolerance. The major implications of the results are:1) the existence of cross tolerance could explain how species are able to survive multiple stress environments, 2) that a set of common underlying physiological mechanisms might exist between apparently divergent stress responses in species, and (3) suggest that stress resistant traits likely coevolved to cope with diverse or simultaneous stressors.