Ontogenetic stage-dependent effect of temperature on developmental and metabolic rates in a holometabolous insect

Different hypotheses attempt to explain how different stages of organisms with complex life cycles respond to environmental changes. Most studies have focused at the among-species level showing similar responses to temperature throughout ontogeny. However, there is no agreement about the pattern expected at the intraspecific scale where a strong selective effect is expected. In this paper, we studied the effects of thermal treatments on a life history trait (developmental rate) and a physiological trait (metabolic rate) during development in the fruitfly Drosophila buzzatii. First, we estimated the rate of development during larval life (LDR) and the pupal stage (PDR) in flies derived from two natural populations exposed to several thermal treatments. Our results showed that the developmental rate ratio, LDR/PDR, did not vary between populations, and that the effects of thermal treatments were stage specific. Second, we studied the relationship between developmental rate (DR) and metabolic rate (MR) in each life cycle stage. We found that allometric relationships between DR and MR varied throughout ontogeny, a pattern that shed light on the mechanisms responsible for thermal plasticity. We conclude that, although different populations may show developmental rate isomorphy; larvae and pupae may choose alternative "decisions" in terms of life-history evolution and physiological traits when confronted to different thermal environments.