With guidance from faculty adviser Dr. William Anderson, graduate student Steven Jessup of the University of Michigan is studying plants of the genus Gaudichaudia of the Malpighiaceae family, a group of flowering vines of the American tropics. Species in this group exhibit several different levels of chromosome doubling, called polyploidy, along with several apparent instances of hybridization between morphologically separate lineages, leading to both sterile and fertile intermediates. The ability of polyploids to produce fertile hybrids between distantly related lineages, and for polyploid hybrids from different progenitors to cross and then backcross to parental tetraploids, results in a genetically complex array of forms where clear morphological boundaries between species are blurred. By using DNA restriction fragment markers and protein electrophoresis in combination with standard taxonomic methods, the researchers will identify and characterize species, and analyze ecological races in terms of geographic range and soil/climate distributions. Using computer-aided methods of phylogenetic analysis, they will infer the origins and evolutionary history of taxa in this genus, and test the hypothesis that the group exhibits a pattern of polyploid cycles of speciation through hybridization. Polyploid cycles have received little attention, especially in tropical woody plants, yet the incidence of high chromosome numbers suggests extensive polyploid evolution in tropical taxa. The new molecular methods in use promise a breakthrough in our understanding of the prevalence and significance of polyploid evolution.
