| dc.description.abstract | Phenotypic plasticity is fundamental in the evolutionary process, as it allows a single genotype to display different phenotypes in response to novel environments. There is a large body of research that demonstrates the ways in which phenotypic plasticity can influence evolution, such as by permitting persistence in novel environments and revealing cryptic genetic variation, which can become genetically assimilated into a population. When plastic responses within a population differ among genotypes, a genotype by environment interaction (GxE) will exist and phenotypic plasticity will have a genetic basis of variation. This genetic basis means that plastic traits are heritable and therefore selection can target both the phenotype that plasticity produces and the plastic response itself. By better understanding the genetic basis of plasticity, the scientific community can hope to further our understanding of the evolutionary process, including how plastic traits are inherited across generations. In this thesis, I use nutritional geometry to examine the role that dietary environment plays in the phenotypic plasticity of maternal investment in the cockroach Nauphoeta cinerea. By creating a half-sib pedigree, I was able to use quantitative genetics to control for individual genotypes, allowing half-siblings to be reared in different nutritional environments (a split brood half-sib design) to judge whether maternal investment varies plastically in response to the nutritional environment, and whether this plasticity has a genetic basis. I used diet eaten per day, gestation period, clutch size, and offspring lipid proportion to measure maternal investment in this study. Specifically, I used two holidic (i.e. chemically defined) diets, one with high carbohydrate content and one with low carbohydrate content, to provide different nutritional environments for the female cockroaches in the experiment. It has previously been shown that many reproductive traits, including gestation period, lipid investment into offspring, and clutch size, for N. cinerea are maximised on high carbohydrate diets, and thus I deemed the high carbohydrate diet a ‘high’ nutritional treatment, and the low carbohydrate a ‘low’ nutritional treatment. I found evidence of phenotypic plasticity in all four of the traits I measured, and evidence of a genetic basis for plasticity (GxE) in diet eaten per day and offspring lipid proportion, but not for gestation period or clutch size. Overall, my thesis provides evidence for a genetic basis of phenotypic plasticity variation in two traits that are fundamentally important for the fitness of an organism, diet eaten per day and offspring lipid proportion. I discovered that maternal investment in N. cinerea responds plastically to the nutritional environment, in that a single genotype can display different phenotypes depending on the diet they receive. As these two traits are linked to fitness and each other, my findings provide evidence that the plastic response to environmental conditions could evolve, producing organisms better able to persist and reproduce in a range of nutritional environments. My findings also support the theory that the role of phenotypic plasticity should be discussed in the Extended Synthesis for the evolutionary process, as these plastic traits are heritable and two show evidence of a basis in the genotype of the organism. Better understanding of the role phenotypic plasticity plays in the evolutionary process could allow us to predict population responses to changing environments, such as those presented by global climate change. | en_GB |
