Evolution of a physiological trade-off in a parasitoid wasp: how best to manage lipid reserves in a warming environment
Résumé
Ectothermic animals, especially insects, are probably the ones most affected, for better or worse, by variable thermic environment, for example in the case of global warming, as their metabolic rate is controlled by the ambient temperature. Parasitoid insects, at the third trophic level, are widely distributed worldwide, and they influence the population dynamics of their highly diverse insect hosts. An important feature of parasitoid wasps is their supposedly limited or non-existent capacity to synthesize lipids during adulthood. As lipid level can be expected to determine whether they engage in maintenance or reproduction, parasitoid wasps are useful biological models for investigating how evolutionary trade-offs in energy allocation to maintenance or reproduction are likely to alter in response to global climate change. To address this, we developed a state-dependent stochastic dynamic programming model, which we parameterized using empirically derived data. The model shed light on the adaptive response of parasitoids with regard to three traits: activity rate, initial egg load, and egg production over the adult female's life span.We show that in a warmer climate, parasitoids devote smaller amounts of lipids to their reproductive effort and favour maintenance over reproduction. However, the bias towards maintenance is reduced when the parasitoids are able to adapt their activity rate to the features of their environment. This model could be tailored to a wide range of organisms with limited energy intake during their adult life.