Date of Award

12-31-2021

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology/Environmental Biology

First Advisor

Rick Kesseli

Second Advisor

Robert Stevenson

Third Advisor

Luis De Léon

Abstract

Dandelions are a weedy, cosmopolitan plant group that has successfully spread across the globe, including seeds found on sub-Antarctic islands. The equation behind the evolutionary success of dandelions may be attributed to its unparalleled dispersal ability, exploitation of mixed asexual-sexual reproductive modes, and perhaps its close association with human migration.

This dissertation explores the population genetics and comparative genomics behind the dandelion’s remarkable biology and resilience. The first research chapter investigates the spatio-temporal genetics of dandelion populations in the local Boston area. Here I utilize deep temporal sampling and find three chloroplast DNA haplotypes, spatial structure across sites, and find that certain genotypes are flowering during specific seasons. Significant amounts of gene flow via dispersal from asexual-sexual sympatric sites in Europe are likely contributing to the vast amounts of local genetic diversity observed. Despite high levels of clonal diversity, microsatellite loci are in linkage disequilibrium suggesting asexual populations. The second research chapter assesses global and continental genetic diversity of dandelions. Again three main cpDNA haplotypes are uncovered, while several rarer ones are found in Europe and Asia; four main microsatellite clusters are found worldwide. The center of diversity is in Europe and Asia, where sexual types are known to occur. Gene flow analyses show panmixia (whether via dispersal or actual sexual reproduction) in all geographic regions except for South American samples from Peru. Contingency analyses for independence between the cpDNA and nuclear genomes split by native and non-native regions show lack of association and implicate sexual reproduction in maintaining genetic diversity. However, linkage disequilibrium tests of only the nuclear microsatellite indicate that regions are asexually reproducing. The third and final research chapter investigates whether two purported species of apomictic, weedy dandelions are truly two different species using molecular methods and morphological assessment. Results of this chapter again show three cpDNA haplotypes, but finds that the two taxa are likely slightly differentiated apomictic lines formed from reticulated evolution as opposed to true biological species.

Comments

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