Date of Award
Doctor of Philosophy
Randall L. Small
Edward E. Schilling, Joseph Williams, Sally P. Horn
The North American plums (Prunus subgenus Prunus section Prunocerasus; Rosaceae) are a closely related group with approximately 17 commonly recognized species and lesser taxa. They are infamous for their very poor development of reproductively isolating barriers and most are interfertile in many combinations. This interfertility blurs nearly all morphologically-based taxonomic boundaries. Even still, geographically related morphological variation exists and when intermediates are ignored several taxa may be seen as being reasonably different from one another with respect to both morphology and ecology. Additionally, the ranges of most of the North American plum taxa overlap with the ranges of several others. The only exception is P. subcordata, which is the only species in the section whose range is west of the Rocky Mountains.
The aim of this dissertation research was to infer a phylogeny for the group in an attempt to understand their complicated evolutionary history. Emphasis was placed on using molecular tools (e.g., PCR and DNA sequencing) to tease apart their intricate relationships. The importance of this course of study includes but is not limited to: (1) better understanding a difficult group of taxa for academic reasons, (2) accumulating data to better understand these taxa so that conservation efforts can be better focused (e.g., P.
geniculate is Federally Endangered), (3) better understanding the relationships among a group of plants with economic importance, (4) testing the limits of tools currently used in plant molecular systematics—the North American plums posit a problem at the boundary between molecular phylogenetics and population genetics, and (5) adding to a body of knowledge surrounding longstanding biogeographic questions of North America, namely the Atlantic and Gulf Coastal Plain disjunction to the Great Lakes region and the eastern North America-western North America disjunction.
This research dissertation is the accumulation of information from four original research papers and a National Science Foundation Dissertation Improvement Grant. All papers have either been published, submitted, or will be submitted to the American Journal of Botany
The results of this coarse of study showed that (1) predictable rate heterogeneity exists among noncoding cpDNA regions and several rarely used regions provide more mutations to phylogenetic investigations than the most commonly used regions (Part 3). (2) The North American plums are monophyletic (Part 4). (3) Most North American plum taxa are para- and polyphyletic with respect to their chloroplasts—more than one of the three primary chloro-haplotypes was observed in 12 of 17 of the North American plum taxa (Part 5). (4) Most North American plum taxa are not monophyletic with respect to their nuclear encoded s6pdh genes—three primary haplotypes are shared among most taxa (Part 6). Total evidence provided by this investigation strongly supports the hypothesis of the North American plums are a syngameon, or hybridizing species group.
Shaw, Joey Thomas, "Systematics of the North American Plums (Prunus subgenus Prunus section Prunocerasus; Rosaceae). " PhD diss., University of Tennessee, 2005.