Document Type

Dissertation

Degree

Doctor of Philosophy

Major

Biology

Date of Defense

4-24-2020

Graduate Advisor

Nathan Muchhala

Committee

Nathan Muchhala

Robert Ricklefs

Maria del Carmen Ulloa

Christine Edwards

Abstract

Genetic structure within and among plant populations is a critical component of plant biodiversity, informing local adaptation, conservation, and incipient speciation. However, its drivers remain poorly understood, especially across different spatial scales. In my dissertation I examined factors that affect plant population genetic structure at global, regional, and local scales. At the global scale, I performed a literature review of population genetic differentiation (FST) in seed plants based on a 337-species dataset with data on FST and species traits. Using phylogenetic multiple regressions, I found that FST is higher for tropical, mixed-mating, non-woody species pollinated by small insects, and lower for temperate, outcrossing trees pollinated by wind. At the regional scale, I tested the effect of flowering asynchrony on genetic divergence between conspecific subpopulations of understory flowering plants in the Andean biodiversity hotspot. I documented flowering phenology for nine species at two sites over one year and inferred population genetic parameters with a genome-wide genotyping approach termed 2b-RAD sequencing. I found that species with higher flowering asynchrony between their subpopulations also show greater genetic divergence. At the local scale, I examined the effect of insect vs. hummingbird pollination modes on the fine-scale spatial genetic structure (SGS) of understory plants in the Andes. I focused on six species for which I confirmed putative pollinators through fieldwork and used the same genotyping technique as above. I found that insect pollination results in a stronger pattern of spatial autocorrelation among closely related individuals, relative to hummingbird pollination. Finally, I investigated the effect of animal pollination mode and latitudinal region on plant SGS, based on a 147-species global dataset. I found that pollination by small insects is significantly associated with stronger SGS relative to pollination by large insects and vertebrates, particularly in understory plants. Likewise, species from tropical regions have significantly greater SGS than species from temperate zones. Thus, factors that affect plant population genetic differentiation are also important for plant SGS. Overall, my findings shed light on the global drivers of genetic structure in plants, and point to important mechanisms for regional genetic divergence and local genetic connectivity in Andean flowering plants.

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