Date of Award

June 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

David Althoff

Keywords

genetic variation, phenotypic plasticity, phenotypic variation, species interaction

Subject Categories

Life Sciences

Abstract

Phenotypic plasticity refers to a genotype’s ability to produce different phenotypes in response to different environments. How organisms respond to environments through phenotypic plasticity can impact the fitness of individuals and thus the demography and even evolution of a population. Having environmentally relevant phenotypic responses could be especially important when a population encounters novel environments, where extinction risks are high such as at the edge of geographic ranges or when there are sudden environmental shifts. Although plasticity has been shown to facilitate the production of novel phenotypes in novel environments, it is less clear whether this leads to increased population survival. The first chapter of this dissertation addresses this question by investigating variation in phenotypic plasticity in a functional trait, alcohol dehydrogenase, and its effect on larval survival of Drosophila melanogaster in a novel alcohol environment. After a population colonizes a novel environment, the population often adapts to this new environment, and phenotypic plasticity has been proposed to facilitate trait evolution. I tested whether phenotypic plasticity could lead to increased fitness when organisms encounter a novel environment. The second chapter examines the genetic architecture of the functional trait alcohol dehydrogenase and its plasticity. Understanding the genetic architecture is important because it can influence the evolutionary response. Specifically, if the functional trait and its plasticity have shared genetic control, their evolution would be tightly linked, which could speed up the rates of evolution if selection on both the trait and plasticity was synergistic or constrain evolution if the direction of selection were divergent. Alternatively, if the trait and its plasticity had different genetic control, plasticity can evolve independently from the functional trait. I used quantitative trait loci mapping with the lines from the Drosophila Synthetic Population Resources to examine genetic architecture in historical and novel alcohol environments. The first two chapters focused on plastic responses to abiotic environments, about which we have a wealth of theoretical and empirical understanding. Natural populations, however, almost never exist alone without interacting with other organisms. Biotic interactions are important drivers of species distributions and trait evolution and new interactions are analogous to novel environments. Biotic interactions are predicted to influence plasticity evolution, but this has been challenging to test and has received little empirical attention. The third chapter explores how biotic interactions may influence trait and plasticity evolution using synthetic yeast (Saccharomyces cerevisiae) communities. I chose to use yeast as a study system because yeast has a short generation time and can be used to form relatively simple replicate communities to isolate the effects of the interaction types. Specifically, I compared competition and mutualism, because they have very different effects on resource dynamics, and I expected them to influence trait and plasticity evolution very differently. I used experimental evolution with communities engaged in either no interspecific interaction, exploitative competition, and resource exchange mutualism. Taken together, this dissertation examines the evolutionary importance of phenotypic plasticity in novel abiotic and biotic conditions and demonstrates that plasticity can be important for both population survival and subsequent evolution in novel environments.

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