Genetic variation in Bromus tectorum (Poaceae) in the Mediterranean region: biogeographical history of native populations

Lauren J. Kelly

The genetic consequences of a species’s introduction into a new range are determined by the amount and distribution of genetic diversity within and among native source populations, size of the founder population, and the number of introduction events. The genetic diversity of native populations is influenced by the species’s mating system and its evolutionary history, especially large-scale biogeographical events. The exceptionally high level of self-pollination (> 99%) in Bromus tectorum contributes to preserving the genetic signature associated with the biogeographical history of its native populations – a history influenced by past climatic events and anthropogenic activity. I characterize here genetic diversity within and among 42 native populations of B. tectorum drawn from two regions: the Eastern Mediterranean Basin (Israel, Jordan, and Syria) and the Western Mediterranean Basin (Portugal, Spain, and France). Two contrasting predictions were tested: 1) populations from the Eastern Mediterranean Basin are more genetically diverse compared with Western Mediterranean Basin populations, a consequence of founder effects during the species’s dispersal with the spread of agriculture and (2) populations from the Eastern and Western Mediterranean Basin contain equivalent genetic vi diversity because both regions served as refugia during glacial advances in the late Quaternary Period. The effects of local factors such as environmental heterogeneity were also assessed, as well as possible pathways of introduction into North America. Eastern Mediterranean Basin populations possess 16 polymorphic loci and 37 multilocus genotypes; populations from the Western Mediterranean Basin have in contrast a subset of these polymorphic loci (9) and fewer multilocus genotypes (19), consistent with the dispersal of B. tectorum with the spread of agriculture. However, 13 of the 19 multilocus genotypes identified in the Western Mediterranean Basin populations are undetected in the Eastern Mediterranean Basin populations. And on average, genetic diversity within populations from Israel, Syria, and Jordan is similar to the genetic diversity in populations from Spain and Portugal. Diversity is lowest for populations from France. These data suggest that glacial history and environmental heterogeneity have also influenced the genetic structure of these populations.

Genetic variation in Bromus tectorum (Poaceae) in the Mediterranean region: biogeographical history of native populations

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