Date of Graduation

8-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Biology (PhD)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Jeremy Beaulieu

Committee Member

Andrew J Alverson

Second Committee Member

Adam M Siepielski

Third Committee Member

Andrew B Leslie

Keywords

biogeography;evolution;meta-analysis;phylogenetic comparative methods;phylogeny;polyploidy

Abstract

Polyploidy, the state of having more than two complete sets of chromosomes, is common in plants and has been linked to several beneficial traits. On the macroevolutionary scale, the effects of polyploidy have been hotly debated for over one hundred years, being alternatively described as an “evolutionary dead end” and the most important discovery in evolutionary biology since Darwin and Wallace. This thesis aims to contribute to the debate by studying the diversification, biogeography, and ecophysiology of polyploid flowering plants with recently developed phylogenetic comparative methods. This dissertation has three chapters. In Chapter I, I review work on the so-called “dead-end hypothesis” in polyploid research, which I argue is in fact multiple hypotheses masquerading as one. I supplement the review with an analysis of tip diversification rates in Solanaceae, employing the MiSSE model. In Chapter II, I examine the “latitudinal polyploidy gradient,” in which polyploid plants comprise greater proportions of the flora at higher latitudes. To compare latitudinal movement and patterns of origination between diploids and polyploids across four flowering plant clades, I use the novel machuruku model to reconstruct ancestral ranges and develop a new function for ancestral state reconstruction within the corHMM package. In Chapter III, I perform the first systematic review and meta-analysis comparing pathogen resistance in diploid and polyploid plants, incorporating phylogenetic information at the family level. Across these three analyses, I do not find support for associations between polyploidy and increased diversification or the evolution of beneficial traits. It is thus possible that any beneficial effects resulting from polyploidy can be chalked up to the “luck of the draw.” Together, these chapters all present novel or under-utilized methods of studying the effects of polyploidy in phylogenetic context.

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