Molecular basis for the co-evolution of thermophysiology and pigmentation in Habrobracon hebetor (Hymenoptera: Braconidae)

Abstract

In the context of global warming and increasing extreme heat, insect responses to temperature include physiological and biochemical changes such as changes in body color. One challenge in biology is to integrate diverse mechanisms of insect plasticity underlying responses to temperature. Life history and trait trade-offs provide a framework for investigating this issue as it relates to the synergistic optimization of related traits. High temperatures during the pupal stage can induce reductions in melanin levels and affect the body color of Habrobracon hebetor adults, with these changes accompanied by enhanced longevity at the expense of fecundity. In our study, we used transcriptome and metabolome sequencing, antioxidant enzyme (SOD, CAT, POD) assays, and additions of exogenous antioxidants, and we found three important relationships: (1) The establishment of heat tolerance in this parasitoid involved responses of antioxidant systems, biogenic amines, and heat shock protein genes, and this tolerance was induced by heat experienced in the pupal stage, with results in the adult stage. (2) A trade-off existed between survival and reproduction based on energy and resource allocation under heat stress. This relationship was disrupted by feeding adults exogenous antioxidants (glutathione and melatonin), as demonstrated by a simultaneous elevation of survival and reproduction at high temperatures. (3) Parasitoid melanosis-related genes (DDC and AANAT) both participated in the regulation of melatonin synthesis. These results enrich our understanding of the theory of plastic body color differentiation in insects and may provide useful insights for the conservation of parasitoids in tropical regions.