Impact of Suburban Landscape Features on Gene Flow of the Model Invasive Grass, <i>Brachypodium sylvaticum</i>

Abstract

Rapid range expansion of newly invasive species provides a unique opportunity for studying patterns of dispersal and gene flow. In this thesis, I examined the effect of landscape features on gene flow in the invasive grass Brachypodium sylvaticum at the edge of its expanding range. I used genome-wide Single Nucleotide Polymorphism (SNP) surveys of individuals from 22 locations in the Clackamas Watershed in the Portland, Oregon metropolitan region to assess genetic diversity and structure, to identify putative source populations, and to conduct landscape genetic analyses. Resistance surfaces were created for each landscape feature, using ResistanceGA to optimize resistance parameters. My STRUCTURE analysis identified three distinct clusters, and diversity analyses support the existence of at least two local introductions. Multiple Regression on distance Matrices (MRM) showed no evidence that development, roads, canopy cover, or agriculture had a significant influence on genetic distance in B. sylvaticum. The effect of geographic distance was marginal and reflected geographic clustering. The model of rivers acting as a conduit explained a large portion of variation in genetic distance. Results indicate that rivers influence patterns of dispersal of B. sylvaticum by human recreational activity centering on use of rivers, and possibly due to movement of deer.