UC Riverside

ABSTRACT OF THE DISSERTATION

Courtship Behavior and Mechanisms of Isolation Across a Hummingbird Hybrid Zone

by

Brian Myers

Doctor of Philosophy, Graduate Program in Evolutionary Biology

University of California, Riverside and San Diego State University, September 2020

Dr. Kevin Burns and Dr. Christopher Clark, Co-Chairpersons

In my dissertation, I focused on the discovery and evolutionary maintenance of a hybrid zone between migratory Allen’s (Selasphorus sasin) and Rufous (Selasphorus rufus) Hummingbird centered in southern Oregon. Via incorporation of morphological, genomic, and behavioral data of 304 birds, my dissertation examines how natural selection, sexual selection, and biogeographic processes have affected the diversification and interactions of Allen’s and Rufous Hummingbird.

In Chapter 1, I used Linear Discriminant Function Analysis (LDA), cline analysis, and a hybrid index to reveal the geographic extent of the Allen’s and Rufous Hummingbird hybrid zone, classify individuals as parents or hybrids, and investigate how selection acts on a suite of behavioral and morphological characters. The contact zone extends north into the breeding range of Rufous, and south into the range of Allen’s. Using geographic cline analysis, I found a role of sexual selection in shaping species barriers.

In Chapter 2, I performed behavioral sequence analysis on Allen’s, Rufous, and their hybrids to assign discrete phenotypes based on the sequences of their courtship displays. For the first time in ethology, I implemented k-mer analysis to identify how many behavioral phenotypes are present across my sampled individuals. I also described novel and transgressive courtship behaviors across the contact zone and found that hybrids are more variable than parental species. At least within Allen’s and Rufous Hummingbird, the modular nature of displays shows that courtship might play a role in diversification between these two species, and possibly within Selasphorus.

In Chapter 3, using whole-genome data, I found evidence of gene flow from Rufous Hummingbird across the range of migratory Allen’s, evidence of intergradation between non-migratory and migratory Allen’s, and high gene flow across the entire non-migratory Allen’s, migratory Allen’s, and Rufous Hummingbird species complex. Further, I found evidence of selection on the Z chromosome in migratory Allen’s and Rufous Hummingbird and estimated divergence dates of Allen’s and Rufous to be further back in time than previously reported.