The genetic and physiological basis of total energy budget in different nutritional environments

Abstract

Organisms need to adapt to dynamic environments over time. An organism consumes and stores a finite amount of resources that are used for all daily tasks. In order to survive and thrive, they must allocate these finite resources to different life history traits like reproduction or somatic growth. In order to understand this process, I examined the genetic and phenotypic variation in macromolecule content, estimated heritability for these phenotypes, and studied the effects of selection on macromolecule content. In my first study, I used the genetic mapping population, the Drosophila Synthetic Population Resource (DSPR), to measure macromolecule content and mapped the genetic loci responsible for carbohydrate, lipid and protein storage on different diets in Drosophila melanogaster. I measured the effect of nutritional environment on overall fly composition. By using the energy budget assays, I showed that there is phenotypic variation in response to diet, the genotypes responsible for nutrient content storage are plastic and that there are multiple genomic loci of interest. Nutrient acquisition increased according to diet composition, with DR having the lowest amount and HS having the highest. The exception to this pattern was glycogen. On the C diet, lipid and carbohydrate amounts correlated together. Overall, protein consistently correlated with all other macromolecules between 0.2 and 0.3 correlation. In my second study, I estimated the heritability of lipid, carbohydrate, glycogen, and protein contents across three different diets using a half-sibling design experiment, using flies from a genetically diverse outbred population generated from the DSPR. I showed differing heritability for different macromolecule contents across nutritional environments. This suggesting not only does nutrient content change based on the particular environment a genotype is in, but that these phenotypes are heritable. In my final study, I tested the effects of female fruit flies undergoing selection for 30 generations. I measured protein, lipid, soluble carbohydrates, and glycogen amount in ovaries and somatic tissue across three different diets across three different selection regimes and found that selection treatments did not significantly impacted macromolecule content. However, diet did. Strikingly, for carbohydrates specifically, patterns of acquisition remained the same in both the base population and after thirty generations of selection regardless of selection regimen. Unlike previous studies, I focused on the impact of diet and measured all four energy budget components on the same individual flies. This allows a wider understanding of resource allocation in different environments. I found that there was variation in macromolecule content acquisition. It is a heritable phenotype, and that diet was more influential in macromolecule content allocation than selection treatment.