Degree

Doctor of Philosophy (PhD)

Department

Biological Sciences

Document Type

Dissertation

Abstract

The remarkable diversity of Neotropical flowering plants has been shaped by a complex interplay of abiotic and biotic factors, including mountain uplift, ecological niche evolution, and shifts between pollinator groups. Yet few studies integrate these drivers across spatial and evolutionary scales within a single clade. Hillieae (Rubiaceae) is a diverse Neotropical tribe comprising ~30 epiphytic species that exhibit spectacular variation in floral morphology, including adaptations to hawkmoth, hummingbird, and bat pollination. While most species occur in low- to mid-elevation wet forests and species richness peaks in southern Central America, the group as a whole occupies a broad range of habitats and abiotic niches. To understand how biogeography, plant-pollinator interactions, and ecological divergence have shaped Hillieae diversification, I integrate target enrichment data, ancestral biogeography and pollination syndrome reconstruction, ecological niche modeling, and multivariate trait analysis. A phylogenetic framework based on ~1000 loci supports multiple shifts in pollination syndromes and a Southern Central American origin ~19 million years ago. Biogeographic reconstructions reveal a history of dispersal and vicariance across geologically complex regions, with pollinator shifts often occurring in distinct geographic and climatic contexts. Zooming in on Hillia subg. Hillia— a clade of nine long-tubed, hawkmoth-pollinated species occurring in diverse habitats along the eastern Andean slopes— I investigate patterns of recent radiation (~5 Mya) and cryptic diversity to understand how mechanisms beyond pollinator-driven selection, which has been common in other subclades, contribute to diversification. Several species overlap in environmental niche and geographic range, and one member of the subgenus, Hillia parasitica, is particularly widespread and exhibits notable intraspecific morphological variation. Phylogenetic analysis reveals that H. parasitica is non-monophyletic with respect to other members of the subgenus, raising questions about species boundaries. To better resolve population structure and delimit species across this subgenus, I integrate SNP data, model-based clustering, species delimitation under varying assumptions of admixture, and analyses of floral and vegetative traits. SNP-based clustering suggests the existence of multiple ecologically and geographically structured lineages. Collectively, this work underscores the value of integrative approaches in understanding plant diversification and sheds new light on the processes generating biodiversity in the Neotropics.


Date

7-13-2026

Committee Chair

Lagomarsino, Laura

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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Available for download on Tuesday, July 13, 2027

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