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Abstract Detail

Population Genetics

Winkler, Daniel E. [1], Chapin, Kenneth J. [2], Garmon, David [3], Huxman, Travis E. [4].

Population genomics and the rapid colonization of Sahara mustard (Brassica tournefortii) in the United States.

Since its introduction in California in the early 20th century, Sahara mustard (Brassica tournefortii) has successfully colonized semi-arid regions eastward from California to Texas and northward into Nevada and Utah. The dispersal and genetic mechanisms that have enabled its success remain unexplored and are a major hurdle in the successful control of the species. The recent, rapid invasion of this species provides an opportunity to address hotly debated questions in invasion biology. We used a next-gen genotyping by sequencing technique to generate reduced representation genomics for 943 individuals from 55 locations and six states across the species’ invaded range to identify population structure and invasion history. Further, we hypothesized that human-mediated dispersal is driving colonization in the US. To address this, we tested for roadways as dispersal corridors as an alternative to isolation by distance models. We used STRUCTURE to infer discrete populations and an analysis of molecular variance to calculate the hierarchical genetic structure within and among locations. Last, we identified introduction, expansion, and admixture events in the species’ history. We identified 1164 single nucleotide polymorphisms across the 55 locations sampled. There was no evidence of isolation by distance among locations, suggesting discrete genetic structure across the range. AMOVA results revealed a significant amount of genetic variation across and within locations. Bayesian clustering analyses using STRUCTURE supports distinct genetic clusters of Sahara mustard in the US. Overall genetic diversity was low across sites, perhaps due to the species dispersal modality and natural history. Surprisingly high heterozygosity across the species range likely indicates admixture of multiple introduction sites after initial invasions. Overall, we found moderate to low levels of genetic structure supporting human-mediated migration along roadways. Sahara mustard has invaded 720,000 sq km across six states and eight ecoregions, despite being introduced in North America as recently as the 1920’s. We present Sahara mustard as an eminently-suited study system to understand invasion evolutionary biology, and discuss our next steps aimed at genomic analyses in the species native range.

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1 - University of California, Irvine, Ecology & Evolutionary Biology, 321 Steinhaus Hall, Irvine, CA, 92697-2525, USA
2 - University of California, Los Angeles, Ecology & Evolutionary Biology, Los Angeles, CA, USA
3 - Tubb Canyon Desert Conservancy, Borrego Springs, CA, USA
4 - University of California, Irvine, Ecology & Evolutionary Biology, Irvine, CA, USA

population genetics
Genetic diversity
genotyping by sequencing

Presentation Type: Oral Paper
Session: 39, Population Genetics
Location: 201/Savannah International Trade and Convention Center
Date: Wednesday, August 3rd, 2016
Time: 8:45 AM
Number: 39004
Abstract ID:937
Candidate for Awards:Margaret Menzel Award

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