The genomic basis of repeated adaptation in deer mice

Abstract

Repeated adaptation to the same environment can drive similar trait changes in independent lineages. This phenomenon, often called convergent evolution, has been observed on a wide variety of timescales, from lineages that diverged hundreds of millions of years ago to contemporary populations evolving in real time. When convergence occurs, it suggests some predictability to the course of evolution and that perhaps the set of possible solutions to a biological problem is constrained. While the selective forces driving convergence may be intuitive, it’s much less clear how, at the molecular level, traits can repeatedly evolve. Even though repeated causal mutations occurring at the same site might seem improbable, it has nevertheless been observed multiple times in long-diverged lineages. At the same time, closely related populations with a considerable amount of shared ancestry have been shown to use different genetic mechanisms to produce the same trait. In this thesis, I explore multiple aspects of convergent evolution in closely related lineages of Peromyscus mice, and describe the molecular mechanisms contributing to repeatedly evolved phenotypes. In Chapter 1, I characterize the repeated independent evolution of two forms of deer mice, forest and prairie, across the species’ range. In Chapter 2, I show that a large chromosomal inversion is associated with multiple trait differences between western forest and prairie deer mice. Finally, in Chapter 3 I examine recently evolved beach mice located in the southeastern United States, and show that a novel enhancer is associated with camouflaging pigmentation in separate populations of these mice.