Energy metabolites mediated cross-protection to heat, drought and starvation induced plastic responses in tropicalD.ananassaeof wet-dry seasons

Cross-tolerance effects for cold and drought stressors are well known for temperate and polar ectothermic organisms. However, less attention has been paid to plastic changes induced by wet-dry conditions for the tropical insect taxa. Drosophila ananassae is abundant in wet habitats but its desiccation sensitivity is likely to make it vulnerable under expected drought conditions due to climate change. We tested plastic effects of heat hardening, acclimation to drought or starvation; and changes in trehalose, proline and body lipids in D. ananassae flies reared under wet or dry season specific conditions. Wet season flies showed significant increase in heat knockdown, starvation resistance and body lipids after heat hardening. However, accumulation of proline was observed only after desiccation acclimation of dry season flies while wet season flies elicited no proline but trehalose only. Thus, drought induced proline can be a marker metabolite for dry season flies. Further, partial utilization of proline and trehalose under heat hardening reflects their possible thermoprotective effects. Heat hardening elicited cross-protection to starvation stress. Stressor specific accumulation or utilization as well as rates of metabolic change for each energy metabolite were significantly higher in wet season flies than dry season flies. Energy budget changes due to inter-related stressors (heat vs desiccation or starvation) resulted in possible maintenance of energetic homeostasis in wet or dry season flies. Thus, low or high humidity induced plastic changes in energy metabolites can provide cross-protection to seasonally varying climatic stressors. Summary statement In the tropical Drosophila ananassae , low or high humidity induced plastic changes in energy metabolites provide cross-protection to seasonally varying climatic stressors