Thermal plasticity of metabolic rates linked to life-history traits and foraging behaviour in a parasitic wasp

Abstract

1. Ectotherm organisms are known to be plastic in their responses to temperature. Individuals developing at low temperatures usually achieve a larger body size through a lower growth rate (‘Temperature Size Rule’, TSR) and, when compared at the adult stage in a common environment, have a higher metabolic rate than those developing at higher temperatures (‘Thermal Compensation Hypothesis’, TCH). 2. For such plastic individuals, increased metabolic rate may incur a switch in the energetic allocation between competing functions such as maintenance and reproduction. Consequently, this differential allocation is expected to affect the animals’ foraging behaviour. 3. This study investigates the effect of developmental temperatures and temperature experienced as adults on metabolic rate, life-history traits and foraging behaviour of females of the parasitic wasp Aphidius rhopalosiphi. For this purpose, individuals were reared at 10, 15, 20 and 25 °C. At emergence, we checked if their traits followed the TSR. We then placed all females in a common environment (20 °C), measured their metabolic rate and examined if a switch of energetic allocation occurred between longevity and/or egg load. Finally, we examined the physiological consequences of temperature on their host patch exploitation behaviour. 4. First, our results showed that traits at emergence followed the TSR. Second, metabolic rates of individuals developing at low temperatures were higher, following the TCH and leading to a reduction in longevity but an increase in oviposition rate. Finally, we showed that patch exploitation behaviours conformed to the predictions of state-dependent foraging models and that hosts which were not exposed to different temperatures, modified their behavioural defences. 5. To our knowledge, this is the first study to demonstrate adaptive thermal developmental plasticity in metabolic rates and its consequences on thermal plasticity of life-history traits and foraging behaviour in ectotherms.