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The massive geographic expansion of terrestrial plant crops, livestock, and marine aquacultured species during the 19th and 20th centuries provided local economic benefits, stabilized food demands, and altered local ecosystems. The invasion history of these translocations remains uncertain for most species, limiting our understanding of their future adaptive potential and historical roles as vectors for coinvaded species. We provide a framework for filling this gap in invasion biology using the widely transplanted Pacific oyster as a case study. A two-dimensional summary of population-level variation in single nucleotide polymorphisms in native Japan reflected the geographical map of Japan and allowed identification of the source regions for the worldwide expansion. Pacific oysters proliferate in nonnative areas with environmental temperatures similar to those areas where native lineages evolved. Using Approximate Bayesian Computation, we ranked the likelihood of historical oyster or shipping vectors to explain current-day distribution of genotypes in 14 coinvaded algal and animal species. Oyster transplants were a more likely vector than shipping for six species, shipping activity was more likely for five species, and a vector was ambiguous for three species. Applying this approach to other translocated species should reveal similar legacy effects, especially for economically important foundation species that also served as vectors for nonnative species. 

Abstract AimAs within‐species genomic data have been shown useful in interpreting broader biogeographic trends, we analysed the mode of population genomic isolation involved in a well‐studied intertidal genomic cline to better understand the mechanisms maintaining it. These results were interpreted in the context of spatial variation in habitat use and availability as well as likely fitness consequences for hybridization between the two lineages. LocationPacific coast of North America. TaxonArthropods (Class Maxillopoda, Order Sessilia, Family Balanidae;Balanus glandula). MethodsGenotype‐by‐sequencing approaches were used to generate single‐nucleotide polymorphism markers across sites sampled between southern Alaska and Southern California. Inference using standard population genomic methods, including analysis of population structure, inbreeding and linkage disequilibrium, was used to identify the steepest transitions across the largest number of loci examined. These data were put in the context of observed population density and habitat availability. ResultsWe show that the majority of markers analysed show strong clinal transitions in a very narrow portion of the California coast. Patterns of linkage disequilibrium among markers, along with prior evidence of variation in reproductive potential by latitude and by mitochondrial lineage, suggest some reproductive isolation among the northern and southern lineages ofB. glandulathat are concordant with the drop in population density and habitat availability in central California. Main ConclusionsA significant clinal transition in genomic diversity is stronger and more localized than previously recognized and exhibits statistical patterns suggesting that the lineages are reproductively and phenotypically distinct in ways that may be ecologically important. As this species has been used to infer process in coastal biogeography, further study of concordant patterns will be important for advancing our understanding of this region.