First name: Quinn
Last name: Evans
Class Year: 2025
Advisor: Jenn Coughlan
Essay Abstract:
How species are maintained in secondary contact is a fundamental question in evolution, and one with important consequences for biodiversity. Finescale ecological divergence is one mechanism of co-existence which requires the evolution of functional traits. Understanding the genetic architecture of divergence can allow us to assess how rapidly this divergence can occur. In this study, we used a pair of sympatric Californian monkeyflowers which differ in ecology and several putatively adaptive phenotypes to explore genetic divergence. We conducted a large common garden experiment with parental species as well as F1 and F2 hybrids and measured 10 reproductive, anatomical, and morphological traits. In contrast to the typically water-dwelling Mimulus guttatus, Mimulus glaucescens (which inhabits drier habitats) flowered early, reproduced via self-fertilization more often, produced fewer and larger stomata, produced epicuticular waxes, and exhibited a unique fused bract at reproductive nodes. By quantifying trait distributions in the F2 generation, we find that a diversity of genetic architectures underlie trait divergence, with many traits appearing largely quantitative. These findings suggest that ecological divergence may have required many mutational steps to achieve. Some traits exhibited strong genetic correlations, suggesting that they share a genetic basis and may represent evolutionary tradeoffs. Abnormal trait distributions and trait combinations in hybrids may have significant implications for selection against hybrids in the field, which may also contribute to species maintenance. This work contributes to a growing literature that suggests that species identity can be maintained in secondary contact, even with complex genetic architectures.