Abstract
The barnacle Chthamalus fragilis is found along the US Atlantic seaboard historically from the Chesapeake Bay southward, and in the Gulf of Mexico. It appeared in New England circa 1900 coincident with warming temperatures, and is now a conspicuous member of rocky intertidal communities extending through the northern shore of Cape Cod, Massachusetts. The origin of northern C. fragilis is debated. It may have spread to New England from the northern end of its historic range through larval transport by ocean currents, possibly mediated by the construction of piers, marinas, and other anthropogenic structures that provided new hard substrate habitat. Alternatively, it may have been introduced by fouling on ships originating farther south in its historic distribution. Here we examine mitochondrial cytochrome c oxidase I sequence diversity and the distribution of mitochondrial haplotypes of C. fragilis from 11 localities ranging from Cape Cod, to Tampa Bay, Florida. We found significant genetic structure between northern and southern populations. Phylogenetic analysis revealed three well-supported reciprocally monophyletic haplogroups, including one haplogroup that is restricted to New England and Virginia populations. While the distances between clades do not suggest cryptic speciation, selection and dispersal barriers may be driving the observed structure. Our data are consistent with an expansion of C. fragilis from the northern end of its mid-19th century range into Massachusetts.
Highlights
Evaluation of population genetic discontinuities and range boundaries in coastal marine species is essential for understanding the consequences of anthropogenic stressors like climate change which may be driving range shifts, poleward range expansions (e.g., Barry et al, 1995; Zacherl, Gaines & Lonhart, 2003; Dawson et al, 2010; Harley, 2011)
The intertidal barnacle Chthamalus fragilis is currently found along the eastern United States, extending from the Gulf of Mexico to the Atlantic coast northward up to Massachusetts (Wells, 1966; Zullo, 1963; Carlton, Newman & Pitombo, 2011), and is thought to be experiencing a northward range expansion linked to warmer temperatures (Wethey, 1984; Carlton, Newman & Pitombo, 2011)
The goals of this study were to investigate the phylogeographic structure of C. fragilis and gain insight into the origin of northern C. fragilis populations by comparing mitochondrial cytochrome c oxidase (COI) haplotypes from several locations in Massachusetts and Rhode Island with those obtained from locations farther south, in Virginia, South Carolina, Georgia, and Florida
Summary
Evaluation of population genetic discontinuities and range boundaries in coastal marine species is essential for understanding the consequences of anthropogenic stressors like climate change which may be driving range shifts, poleward range expansions (e.g., Barry et al, 1995; Zacherl, Gaines & Lonhart, 2003; Dawson et al, 2010; Harley, 2011). Prior to the late 19th century, C. fragilis was observed from the Chesapeake Bay area and southward It was first observed in New England (Woods Hole, Massachusetts) in 1898, and subsequently was observed in other locations south of Cape Cod, in Buzzards Bay and Vineyard Sound (Carlton, Newman & Pitombo, 2011). It is found along the north shore of Cape Cod, from the outer Cape (Provincetown) to Sandwich at the northern end of the Cape Cod Canal (Zullo, 1963; Carlton, 2002; Wethey, 2002; Jones, Southward & Wethey, 2012). C. fragilis is a conspicuous species occupying the accessible upper intertidal, so it is unlikely that an earlier northern presence was overlooked, as the Woods Hole region has a long history of faunal surveys
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