Abstracts (first author)
Experimental insight into condition-dependent trait expression: near-orthogonal effects of environmental vs. genetic manipulations in Drosophila melanogaster
Differences in condition among individuals arise from both genetic and environmental variance in their acquisition and/or assimilation of resources. Such variation in condition can weaken or otherwise obscure the physiological trade-offs among competing life history traits that are thought to necessarily arise from the allocation of finite resources. The nature and extent of among-individual variation in condition will therefore determine whether life history traits co-vary positively or negatively and is therefore central to our understanding of life history trade-offs. Our understanding of condition-dependent trait expression derives almost exclusively from environmental manipulations, yet it is the underlying genetic basis of condition, and the pleiotropy this generates among life history traits, that may have fundamental evolutionary consequences. A comprehensive understanding of life history traits, their trade-offs, and their evolution, will therefore require a detailed knowledge of the impacts on trait expression of both environmental and genetic variation in condition. Here we use a two-way factorial design to provide some of the first experimental data comparing the effects of diet and mutation-accumulation (i.e. environmental and genetic) manipulations of condition on a suite of sexual displays (epicuticular pheromones) and morphological traits in Drosophila melanogaster. Our results reveal that condition is multi-dimensional, with the effect of the environmental manipulation being almost orthogonal to that of the genetic manipulation for both sets of traits in both sexes. Only body size showed concordant effects of diet and mutation accumulation. This suggests that environmental manipulations alone may provide misleading insight into condition-dependence and its effects on the expression, evolution, and trade-offs among competing traits.