Multiple spatially distinct introductions and not range expansion may explain colonization history in a non-native marine shrimp

Abstract

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.