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Abstract
Pollinator interactions are key to understanding plant evolution across space and time. One prominent question is how plants evolve under a geographic mosaic of pollinators at the macroevolutionary scale. In this dissertation, I examine the interplay among pollinator interactions, geography, floral traits, and speciation in Southeast Asian sunbird-pollinated Aeschynanthus (Gesneriaceae). Integrating comparative approaches with ecological experiments, I focused on divergence and pollinator shifts in the morphologically and geographically distinctive A. acuminatus and its closest relatives. In Chapter 1, I tested macroevolutionary predictions of the classic pollinator-mediated speciation model in the origin of A. acuminatus. Phylogeographic analysis of genome-wide SNPs revealed that the species did not originate beyond the sunbird range and did not support the model’s prediction. Using hypothetical pollinator-mediated fitness models, I proposed an alternative scenario to explain its shift to a mixed vertebrate pollination system in the presence of ancestral sunbird pollinators. In Chapter 2, I investigated the role of pollinators in the divergence and speciation of A. acuminatus and its two closely related species, A. moningerae and A. pedunculatus. Phylogenetic reconstruction demonstrated expansion and contraction of pollinator niche breadths concurrent with a series of speciation events in the three focal species. However, pollinator shifts alone did not lead to the absence of gene flow unless complemented with geographic or phenological isolation. In Chapter 3, I focused on the divergence between A. acuminatus and A. moningerae to investigate how differences in floral traits determine their pollinator assemblages and visiting behavior. Predominant sunbird visit by hovering affirmed the prediction that long peduncles in A. moningerae restrict access by antagonistic floral visitors and demonstrated that sunbirds can act as hovering pollinators analogous to hummingbirds. Across chapters, I presented cases of speciation with pollinator shifts—such as in A. acuminatus and A. moningerae—cannot be fully explained by the classic pollinator-mediated speciation model. Instead, alternative hypotheses derived from the hypothetical fitness landscapes in Chapter 1 suggest future directions that consider temporal mosaics in pollinator availability. These ideas invite further testing through microevolutionary approaches. Finally, this dissertation underscores the enduring value of natural history observations, which both challenge and enrich theoretical predictions.