Sex, diet, health and lifespan in the fruit fly, Drosophila melanogaster

Nutrition is a vital determinant of lifespan, reproduction, health and ageing. Much has been done to investigate the lifespan consequences of short-term (proximate) nutritional manipulation, but much less is known about long-term (evolutionary) nutritional manipulation and nutritional mismatches. In this thesis I addressed this important omission, using the fruit fly, Drosophila melanogaster, model system. I empirically tested two evolutionary theories: the Thrifty Phenotype and Thrifty Genotype hypotheses, which predict the general life history consequences of nutritional mismatches over the lifetime or over evolutionary time, respectively. I also tested how the latter interacted with long-term nutritional selection regimes. Contrary to predictions, I showed that the costs of nutritional mismatches between developmental and adult diets were not universal, but instead dependent on the nature of the mismatch, sex and the components of life history measured (Chapter 2). Similarly, the costs of mismatches between evolved and proximate nutrition were dependent on evolved feeding regime, sex, life history component measured and proximate diet (Chapter 3). I discovered that there was enhanced sexual dimorphism for lifespan in nutritionally selected lines, which was associated with sex-specific life history patterns and a partial resolution of sexual conflict (Chapter 4). Transcriptome-wide analysis of these nutritionally selected lines revealed differential expression in genes with functions related to lifespan, post-mating responses, regulation and epigenetic modification (Chapter 5). Finally, I found that manipulation of another important component of altered lifestyles, activity level, had no effect on lifespan or reproduction (Chapter 6). Overall, my results make a novel contribution to the study of nutritional mismatches and long-term nutritional selection. The results also highlight the importance of simultaneously studying both sexes and several age-specific components of life history, in different proximate environments, to fully elucidate the fitness consequences of nutritional manipulation