title: Are genes faster than crabs? Mitochondrial introgression exceeds larval dispersal during population expansion of the invasive crab Carcinus maenas.
abstract: Biological invasions offer unique opportunities to investigate evolutionary dynamics at the peripheries of expanding populations. Here, we examine genetic patterns associated with admixture between two distinct invasive lineages of the European green crab, Carcinus maenas L., independently introduced to the northwest Atlantic. Previous investigations based on mitochondrial DNA sequences demonstrated that larval dispersal driven by advective currents could explain observed southward displacement of an admixture zone between the two invasions. Comparison of published mitochondrial results with new nuclear data from nine microsatellite loci, however, reveals striking discordance in their introgression patterns. Specifically, introgression of mitochondrial genomes relative to nuclear background suggests that demographic processes such as sex-biased reproductive dynamics and population size imbalances-and not solely larval dispersal-play an important role in driving the evolution of the genetic cline. In particular, the unpredicted introgression of mitochondrial alleles against the direction of mean larval dispersal in the region is consistent with recent models invoking similar demographic processes to explain movements of genes into invading populations. These observations have important implications for understanding historical shifts in C. maenas range limits, and more generally for inferences of larval dispersal based on genetic data.
authors.affiliation: National Exposure Research Laboratory, United States Environmental Protection Agency , 109 TW Alexander Drive, Durham, NC 27711, USA.
authors.forename: John A
authors.initials: JA
authors.lastname: Darling
authors.affiliation: Department of Ecology and Evolutionary Biology , University of Colorado , Boulder, CO 80309, USA.
authors.forename: Yi-Hsin Erica
authors.initials: YH
authors.lastname: Tsai
authors.affiliation: Department of Biology , Long Island University , 720 Northern Boulevard, Brookville, NY 11548, USA.
authors.forename: April M H
authors.initials: AM
authors.lastname: Blakeslee
authors.affiliation: Gund Institute for Ecological Economics, University of Vermont , Burlington, VT 05405, USA.
authors.forename: Joe
authors.initials: J
authors.lastname: Roman
keywords: admixture; introgression; invasive species; range expansion