| dc.description.abstract | Life-history traits form an integral part of evolutionary biology as they closely relate to an individual’s fitness. There is a huge archive of empirical research that has shown diet influences the expression of nearly all life-history traits, ranging from immune response to sperm number. Exactly how diet actually influences the expression of important life-history traits, however, is often poorly understood, as traditionally diet has been viewed in a one-dimensional context, namely energy or calories. More recent research has begun to challenge this notion, by suggesting that it is actually the intake of specific nutrients that influences trait expression and fitness. Clearly, our understanding of the role of diet is shifting, yet more empirical studies are needed, which focus on how the intake of specific nutrients influence key life-history traits, whether these regulate life-history trade-offs and how this may impact an individual’s fitness.
In this thesis, I use the Geometric Framework (GF) of nutrition to examine the role nutrition plays in the expression of key life-history traits (reproduction and lifespan) and any trade-offs that may exist between them. Historically, the type of diet used in some nutritional studies has been suboptimal, with some researchers proposing that CAFÉ assays, in particular, effect trait expression in Drosophila melanogaster. This is because they are a foreign substrate for the fly to feed from and thus it is difficult for flies to acquire the nutrients they need to function properly. Therefore, I formulated novel diets that represent the smallest deviation from natural feeding conditions, when compared to previous nutritional research, for D. melanogaster. I used these diets to focus on the effect two macronutrients, protein and carbohydrate, have on lifespan and reproduction in male and female D. melanogaster. I found that both protein and carbohydrates play a role in the expression of these traits, and not calories per se, and that there are divergent nutritional demands for reproduction between the sexes. I also found evidence that implies the type of diet (liquid versus medium-based) used to study nutritional effects on life-history traits could influence findings, with flies fed a medium-based diet living longer and having greater reproductive success. This could possibly be due to greater nutrient acquisition by flies fed medium-based diets.
Overall, my thesis highlights that nutrition is multifaceted and complex, which is paramount to understanding life-history trait expression and the trade-offs that may exist between them. My work challenges the central dogma that calories are responsible for changes in trait expression and life-history trade-offs, and advances our understanding of diet composition and also the way that diet is delivered to organisms. In addition, it opens the door to new questions relating to how the type of diet and nutrient composition effect not only lifespan and reproduction but other life-history and sexually selected traits as well. | en_GB |
