Intellectual Merit: The duplication of chromosome sets (polyploidy) and interspecific hybridization are critical mechanisms known to generate novel genotypes and species diversity. Furthermore, recent advances in genomic techniques and data analysis have suggested that polyploidy and hybridization played more fundamental roles in major evolutionary events than previously recognized. These discoveries along with the tremendous range of consequences induced by these mechanisms identify that we are only touching the tip of the iceberg when it comes to both our understanding of the distribution of hybridization and polyploidy and their potential actions. In this proposal I outline a project whose goals are to advance the understanding of the distribution of these phenomena as well as the application of new tools in research programs focused on relationships among closely related plant species. Through this work I intend to elucidate relationships among divergent and reticulate species in the legume genus Leucaena, a group that has been a focus of my recent research program and that will form a core component of future studies.
The Study System: The 22 species of Leucaena include presumed extant divergent diploid progenitors with derived taxa/individuals of hybrid, autopolyploid, and allopolyploid origins all within a fairly restricted geographic distribution. The prevalence of hybridization and polyploidy among species of Leucaena (Fabaceae) help to make it an important system in the study of plant evolutionary biology. In addition, general interest in systematic research on Leucaena has been sparked by connections to ongoing indigenous plant domestication and the status of some taxa as invasive weeds in the tropics. Several studies have attempted to elucidate the origins of polyploid and hybrid species of Leucaena; however, a lack of sufficiently variable data continues to hinder the development of clearly supported hypotheses that are critical for the understanding of their origin(s) and subsequent study on the specific impact of these mechanisms on evolution.
Objectives: The specific research objectives of this proposal are to: 1) use a novel strategy to develop multiple sufficiently variable DNA sequence based data sets from Leucaena to fully investigate divergent and reticulate relationships among taxa; 2) demonstrate the utility of the novel SCAR-based strategy in phylogenetic studies; 3) complete a web-based database that will facilitate the dissemination of the growing body of information on Leucaena to the broader research community; and 4) educate and inspire undergraduate and graduate student participants from a minority serving institution.
Broader impacts: Findings from this study will provide critical evidence for the general role of hybridization and polyploidy in a genus of chiefly neotropical trees that includes species undergoing domestication. In addition, the tools developed will help to address problems resolving phylogenies that have been commonplace in angiosperm systematics. The funding and implementation of this project will generate training and educational opportunities for graduate and undergraduate students at a minority serving institution in a laboratory with a record of attracting and training individuals who represent minority groups. All students involved in this project will develop expertise in taxonomy, systematics, molecular biology, and bioinformatics.
Furthermore, the completion of the data base on Leucaena will supply a comprehensive global resource for information on this developing system that will ideally attract the attention of other researchers interested in using Leucaena to study the genomic impacts of hybridization, polyploidy, and domestication.
