Date of Graduation

Spring 5-23-2026

Document Type

Thesis

Degree Name

Master of Science in Biology

College/School

College of Arts and Sciences

First Advisor

John R. Paul

Second Advisor

Sevan Suni

Third Advisor

Scott Nunes

Abstract

Islands, with their isolation and steep environmental gradients, serve as natural laboratories for studying speciation. Molecular phylogenetic and population genetic methods utilizing Next-Generation Sequencing (NGS) have revolutionized our ability to document patterns of genetic divergence and diversity. Cryptic diversity, genetically distinct populations that were previously unrecognized as unique, and cryptic speciation, where divergent genetic populations may be deserving of status as unique species, have been observed in many taxa. The Hawaiian Islands provide an ideal setting for studying divergence and speciation due to their extreme isolation, known ages, and volcanic origin. Previous work has investigated the evolutionary relationships of the 11 named endemic species of Psychotria on the Hawaiian Islands using molecular phylogenetics. The research has confirmed a single origin of the Psychotria diversification and may indicate the presence of cryptic diversity in Psychotria mariniana, one of the widespread species. This species has been extensively sampled across the Hawaiian Islands, and the genetic divergence between its populations exceeds the divergence between other Hawaiian Psychotria species, based on ribosomal and chloroplast DNA data in past studies. However, the lack of molecular markers with sufficient genetic variation has limited strong inferences about patterns of divergence. To overcome this limitation, I investigated the possibility of cryptic divergence in P. mariniana using two NGS approaches, double-digest restriction-associated DNA sequencing (ddRADseq) and whole-genome sequencing (WGS). I hypothesized that the genetic divergence between different P. mariniana populations is equal to or greater than that of populations of different Hawaiian Psychotria species. This study confirmed substantial intra-island genetic diversity, clarified previously unresolved or contradictory phylogenetic relationships, and suggested a more complex origin scenario for Hawaiian Psychotria than previously thought. Rather than a simple Kaua‘i-first model, the data support an early divergence between O‘ahu and Kaua‘i lineages, with one giving rise to younger island populations and the other diversifying further on Kaua‘i, possibly including the origin of P. wawrae. These findings provide insights into the conservation and management of the endemic Psychotria diversity on the Hawaiian Islands. By revealing cryptic genetic structure and highlighting distinct lineages that had not been formally recognized, this work has the potential to inform taxonomic reevaluation and support efforts to revise protection status for certain populations. In testing low-coverage whole-genome sequencing in this system, this study offers a starting point for future work on genome-wide variation in Psychotria and potentially other non-model tropical plants. The resulting genome will be made available as a resource for further studies and guiding future research in both Hawaiian biogeography and Rubiaceae systematics.

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