Multiple spatially distinct introductions and not range expansion may explain colonization history in a non-native marine shrimp
Biological invasions are often characterized by a phase of post-establishment expansion in which the invading species increases its range through colonization of new geographic areas. These expansions are predicted to result in specific genetic signatures, most notably decreased genetic diversity with distance from the point of introduction. The Asian caridean shrimp Palaemon macrodactylus is an introduced species in many regions of the globe. It has most recently invaded the U.S. Atlantic coast, with the first reported sighting in New York in 2001. This study used mitochondrial cytochrome oxidase I sequence data and data for 1598 single-nucleotide polymorphisms generated through restriction enzyme-associated DNA sequencing to evaluate two potential invasion mechanisms describing the spread of P. macrodactylus north of New York: the first based on a single introduction followed by range expansion facilitated by ocean currents, coastal transport, and physical environment; the second based on multiple introductions from overseas into different ports along the coast. We compare population genetic results to predictions of genetic patterns for each of these potential invasion pathways. Results do not support range expansion in which diversity decreases with distance from the point of first detection. Rather, the data suggest that multiple introductions may have taken place with population genomic diversity increasing with distance from New York, and peaks of mitochondrial diversity in populations collected from New York and the Boston–Plymouth coastline. These results indicate that multiple human-mediated dispersal events may be as important as oceanographic and life history considerations during the colonization phases of a marine invasion.
We thank the exuberant field assistance provided by the many members of the “ShrimpEX2014” research team, based out of the Williams College-Mystic Seaport Maritime Studies Program in Mystic, Connecticut. Support was provided for the ShrimpEX2014 research program by the Massachusetts Office of Coastal Zone Management and the Northeast Sea Grant Consortium. This research is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. 1122374. Funding for the RAD-sequencing was provided in part by the Woods Hole Sea Grant Program, and the Woods Hole Oceanographic Institution Biology Department. Additional support was provided by the National Science Foundation (OCE-1131620 to TMS) and the James Education Fund for Ocean Exploration within the Ocean Exploration Institute of the Woods Hole Oceanographic Institution. We would like to thank the editors and reviewers for Marine Biology who contributed insight and perspective to this manuscript.
Eleanor K. Bors (EKB) conceived of the project with substantial input from James T. Carlton (JTC) and Timothy M. Shank (TMS). JTC and EKB planned and undertook sample collection. EKB undertook the laboratory work and data analysis for the genetic and genomic data. EKB, JTC, and TMS discussed interpretation of the data. JTC and TMS both provided support for the project from assistance in the field to laboratory materials.
Compliance with ethical standards
Conflict of interest
All funding is listed in the acknowledgements section. The authors declare that they have no conflict of interest.
All guidelines for the sampling of organisms were followed. Collecting permits were obtained for New Hampshire, Massachusetts, Rhode Island, Connecticut, and New York, copies of which are available upon request.
Data availability statement
Data have been made available online on GenBank (BioProject ID PRJNA521400). As noted in the text, some accession numbers are already available online for mitochondrial data. Scripts used in analysis are available on the author’s GitHub page accessible via the following link: https://github.com/ekbors/p_macrodactylus-.
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