Origins and Hybridization of Invasive Saltcedar (Tamarix) Inferred from DNA SequencesEPA Grant Number: U915573
Title: Origins and Hybridization of Invasive Saltcedar (Tamarix) Inferred from DNA Sequences
Investigators: Gaskin, John F.
Institution: Washington University
EPA Project Officer: Broadway, Virginia
Project Period: August 1, 1999 through August 1, 2002
Project Amount: $79,896
RFA: STAR Graduate Fellowships (1999) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Ecology and Ecosystems
The objective of this research project is to determine the specific identity and Eurasian origins of invasive saltcedar populations, and investigate putative post-introduction hybridization between historically separated species.
This project will be the first application of molecular sequence data and phylogeography for invasive plant research. Vouchered DNA samples will be used to compare the range of DNA sequences of the invasive specimens with that of different suspect Old World species, unambiguously elucidating the taxa or taxon that comprise the invasions. For the phylogenetic analyses, the investigator will sequence the nuclear ribosomal internal transcribed spacer (ITS) region and a chloroplast transfer RNA gene, which give resolution at the species level. Parsimony analysis will be used to illuminate interspecific relationships and any putative hybridization events. To pinpoint invasive population origins the ppcL locus (the fourth intron of phosphoenolpyruvate carboxylase) will be sequenced, which has shown variation at the population level in selected Tamarix species. DNA sequences will be used to perform a coalescent-based analysis of allele genealogies (also called a haplotype tree). The geographic structuring of haplotypes then will be assessed to discern if population-specific geographic origins of invasive haplotypes correlate with their position on the haplotype tree.
Post-naturalization hybrid events will be revealed if an invasive or naturalized specimen contains a chloroplast sequence belonging exclusively to the native genotype of one species, and a nuclear sequence belonging exclusively to the native genotype of a different species (phylogenetic incongruence), or if an invasive or naturalized specimen contains nuclear haplotypes corresponding exclusively to the native genotypes of two different species (nuclear heterozygosity).