ORCID

0000-0001-7299-2991

Keywords

hawkfish, color, polymorphism, genome, ecology, evolution

Abstract

Color polymorphism provides a tractable window into how selection, gene flow, and ecology interact to maintain phenotypic diversity and initiate divergence. I investigate the ecological and genomic basis of sympatric light and melanistic morphs in two reef hawkfishes, Paracirrhites arcatus and P. hemistictus, across Guam and Hawai‘i. This study aims to determine whether the color morphs of these hawkfishes are a stable polymorphism or have begun the process of ecological speciation. For P. arcatus revealed substantially lower density on Guam (0.086 ind/m²) than reported for Hawai‘i (0.292 ind/m²) and a strong skew away from the melanistic morph on Guam (7.0%) relative to Hawai‘i (39.6%), indicating geography‑dependent morph structure and habitat context. Redundancy analysis showed that a simplified model explained slightly more variance than the model developed for the Hawaiian population, while multidimensional niche‑overlap tests detected significant differentiation among morphs despite weak univariate habitat preferences. Whole‑genome resequencing (148 genomes) recovered modest population differentiation (Guam-Hawai‘i mean FST = 0.0047) and slightly higher between‑morph genome‑wide FST on Guam (0.0015) than Hawai‘i (0.0010). Sliding‑window scans and SNP outlier tests identified numerous regions of elevated differentiation, including pigmentation genes (e.g., gpnmb, sox9, sfxn1), supporting “islands of divergence” under gene flow. In P. hemistictus (69 genomes), morph divergence was markedly greater (mean FST = 0.0750), with spatial sorting across Orote Peninsula and selective signatures (e.g., Chd1) pointing to more advanced separation without single diagnostic loci. Together, these results show that similar light/melanistic polymorphisms can follow distinct trajectories driven by ecological conditions and including competitive environments. Sympatric incipient divergence is supported in P. arcatus, particularly in Hawai‘i, while there is deeper genome‑wide separation in the morphs of P. hemistictus.

Completion Date

2026

Semester

Spring

Committee Chair

Michelle Gaither

Degree

Doctor of Philosophy (Ph.D.)

College

College of Sciences

Department

Biology

Format

PDF

Document Type

Dissertation

Identifier

DP0053259

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