Date of Award
Spring 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Ecology and Evolutionary Biology
First Advisor
Post, David
Abstract
Eco-evolutionary feedbacks describe how ecology and evolution reciprocally act upon each other to bring about adaptive evolution over ecological timescales. Two conditions or steps define eco-evolutionary feedbacks: (1) an organism’s phenotype must interact strongly with its environment so as to construct or structure it, and subsequently, (2) the newly constructed environment must introduce new selection pressures that result in the population’s adaptive evolution. Eco-evolutionary feedbacks have been discovered in numerous taxa, including fish, bacteria, cancer cells, and plants. Despite the growing number of examples, the prevalence of eco-evolutionary feedbacks in nature is still unknown. Each step of an eco-evolutionary feedback is likely contextually dependent. If either condition of the feedback is not met, the feedback will decouple, and the reciprocal relationship between ecology and evolution will cease. Understanding the contexts that mediate the conditions of eco-evolutionary feedbacks can lead to predictions about their strength and incidence and in nature, and to their discovery in other organisms. The alewife (Alosa pseudoharengus) is a clupeid fish native to the Atlantic Coast of North America and is an archetypal organism for studying eco-evolutionary feedbacks in nature. Alewife exhibit two life histories. Anadromous alewife move between marine and freshwater habitats and landlocked alewife spend their entire life cycle within freshwater lakes. Through size selective foraging, alewife shift the size of the zooplankton community toward smaller bodied individuals. Landlocked alewife live year-round in their constructed environment and are thus subjected to increased selection on foraging traits like gill raker spacing to handle smaller bodied zooplankton. In response to this increased selection, landlocked alewife adapt smaller gill raker spacing, among other traits, creating intraspecific variation between anadromous and landlocked populations. Here, I analyze the context dependency of eco-evolutionary feedbacks in alewife to understand the origins of their intraspecific variation. I present evidence for the context dependency of eco-evolutionary feedbacks in four chapters. In chapter 1, I show that the alewife’s effects on zooplankton community size structure can be used by ecosystem managers to monitor their presence or absence within freshwater lakes. I compare and contrast this with direct sampling by purse seine and environmental DNA, and show that sampling alewife through their environmental effects is the most efficient and effective method for alewife biomonitoring. In chapter 2, I show that ecosystem size mediates landlocked alewife’s environmental effects through studying zooplankton heterogeneity across a lake size gradient. In small lakes, alewife’s environmental effects are strong, but their effects weaken as lake size increases. In chapter 3, I propose a framework for understanding the mechanism by which strong organism-environment interactions lead to changes in selection pressures Through their strong effects on zooplankton, alewife push their fitness optima away from themselves, resulting in stronger selection and evolutionary responses. In chapter 4, I show that landlocked alewife in small lakes have smaller gill raker spacing than in large lakes, and present evidence that lake size mediates alewife eco-evolutionary interactions. Taken together, these findings highlight the context dependency of eco-evolutionary feedbacks in alewife.
Recommended Citation
Dougherty, Matthew Michael, "Context Dependency of Eco-Evolutionary Feedbacks in Alewife (Alosa pseudoharengus)" (2023). Yale Graduate School of Arts and Sciences Dissertations. 942.
https://elischolar.library.yale.edu/gsas_dissertations/942
