Identifying the Geographic Origins for the Introduction of \u3cem\u3eTaeniatherum caput-medusae\u3c/em\u3e subsp. \u3cem\u3easperum\u3c/em\u3e (Medusahead) in the Western United States

The use of molecular markers can provide insights into the demographic and evolutionary processes that have shaped the genetic diversity of native populations and can be used to identify an invasive species’ geographic origins. Taeniatherum caput-medusae subsp. asperum (medusahead) is a cleistogamous, diploid, annual grass native toEurasia that is now invasive in the western United States (U.S.). Enzyme electrophoresis methods (allozymes) have previously been used to analyze both native and invasive populations of medusahead. Results from these studies suggest that the invasion of medusahead in the westernU.S. stems from multiple introduction events. In addition, 10 of 34 populations from across the native range of the species possessed multilocus genotypes that match some of those detected in invasive populations, with six of these putative source populations located inGreece andNorthwestern Turkey. The overall objective of the current study is to better circumscribe the geographic origins for this invasion through allozyme analysis of 48 native populations of medusahead from Southeastern Europe (Albania, Bulgaria, Greece, Macedonia, Romania, Serbia, Northwestern Turkey, and Ukraine) and South-central Turkey. Among the 48 native populations I analyzed, a total of 35 multilocus genotypes were detected, with four of these genotypes matching those previously reported among invasive populations. Forty of the 48 (83.3%) native populations contained at least one individual with a multilocus genotype matching a genotype reported among invasive populations. The 48 populations from Southeastern Europe andSouth-central Turkey exhibit less genetic structure and display lower levels of genetic diversity compared with the 34 native populations previously analyzed. Also, the genetic diversity of these 48 populations is not geographically structured; it does not conform to an isolation-by-distance pattern. Taken together, results from this study suggest that the geographic origins of this invasion occur broadly across the study region. In addition, the genetic diversity of these 48 native populations appears to be influenced by stochastic demographic processes in which an individual or individuals with various genotypes randomly colonizes disturbed sites and establishes a population. This process has led to an intermixing of genotypes within and among populations across the study area. Because allozymes typical underestimate the genetic diversity of populations, the findings of this study should be assessed using a molecular marker with greater resolving power (i.e., amplified fragment length analysis)