Abstract

Variation in body size and body shape underlies much of the diversity observed between insect species. This variation in body size/shape results from genetic variation between and within species, but also from environmentally induced variation that can cause dramatic changes in phenotype within a single genotype. We are interested in how the developmental mechanisms that respond to environmental change, also known as phenotypic plasticity, correlate with the genetically determined variation in phenotype between and within species. Here, we will explore an example of how developmental processes in the ovary are affected by both environmental and genetic variation to generate a range of ovary sizes. We used the fruit fly Drosophila melanogaster to first identify phases of sensitivity to nutrition that contribute to plasticity ovary size, and to uncover three developmental processes affected by nutrition. We further determined the role of two nutrition-responsive signalling pathways, the ecdysone signalling and the insulin/insulin-like growth factor signalling (IIS) pathways, in regulating each of these developmental processes, thereby determining ovary size. Next, we explored if the developmental processes affected by nutrition also account for genetic differences in ovariole number between two subspecies of Drosophila mojavensis, D. moj. sonorensis and D. moj. wrigleyi. This characterization revealed that all three developmental processes differ between subspecies. Nevertheless, divergence in ovary growth rates appears to underlie much of the variation in ovariole number. These data suggest that genetic variation in ovariole number between these subspecies results from a subset of the processes involved in the plastic response to nutrition. Further experiments are required to determine whether the same signalling pathways, ecdysone signalling and IIS , are also underlie genetic variation in ovariole number.