Degree

Doctor of Philosophy (PhD)

Department

Biology

Document Type

Dissertation

Abstract

The emergence of novel pathogens can impose intense selective pressures on natural populations, driving rapid evolutionary change or precipitating population collapse. In Hawaiʻi, the introduction of avian malaria (Plasmodium relictum) and its mosquito vector (Culex quinquefasciatus) have caused severe declines and extinctions among native forest birds. Yet some populations of Hawaiʻi ʻamakihi (Chlorodrepanis virens) persist across a broad elevational and disease gradient, providing a powerful natural system for examining the genomic basis of rapid adaptation, the role of gene flow in adaptive response, and the potential for parallel evolutionary responses. This dissertation integrates genomic, population genetic, and transcriptomic approaches to investigate the mechanisms underlying evolved malaria tolerance in Hawaiʻi ʻamakihi. First, whole-genome sequencing of experimentally infected individuals was used to identify genetic variants associated with malaria immunity. Association analyses revealed a polygenic basis of immunity involving genes linked to immune regulation, including both previously implicated malaria-related genes (e.g., TLR4, IL15, CD99L2) and novel candidate loci, highlighting the complex genomic architecture of rapid adaptation. Second, population genomic analyses assessed connectivity across low-, mid-, and high-elevation populations on the island of Hawaiʻi. Genome-wide SNP data revealed minimal population structure, low genetic differentiation, and widespread bidirectional gene flow across elevations. These findings indicate that disease-mediated selection has not resulted in strong genetic isolation and suggest that immune-associated alleles may spread across the elevational gradient, potentially facilitating evolutionary rescue as climate change expands malaria transmission into higher elevations. Finally, transcriptome sequencing of Hawaiʻi ʻamakihi from Maui examined gene expression differences across regions of varying malaria prevalence. Differential expression analyses identified immune-related genes involved in signaling, ubiquitination, autophagy, and T-cell regulation, with patterns paralleling immune-associated pathways identified on the island of Hawaiʻi. These results provide evidence for parallel evolution of similar immune responses across islands despite geographic isolation. Together, this dissertation demonstrates that malaria tolerance in Hawaiʻi ʻamakihi arises from a combination of polygenic adaptation, high population connectivity, and repeated evolution of shared immune pathways, offering rare insight into contemporary natural selection in response to an emerging infectious disease.

Date

2-6-2026

DOI

https://proquest.com/docview/3347903254

First Committee Chair

Loren Sackett

First Committee Member

Andrea Westerband

Second Committee Member

Melissa Toups

Third Committee Member

Ole Seehausen

Fourth Committee Member

Swanne Gordon

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