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Phylogeographic structure and northward range expansion in the barnacle Chthamalus fragilis.

Govindarajan AF, Bukša F, Bockrath K, Wares JP, Pineda J - PeerJ (2015)

Bottom Line: The barnacle Chthamalus fragilis is found along the US Atlantic seaboard historically from the Chesapeake Bay southward, and in the Gulf of Mexico.We found significant genetic structure between northern and southern populations.While the distances between clades do not suggest cryptic speciation, selection and dispersal barriers may be driving the observed structure.

View Article: PubMed Central - HTML - PubMed

Affiliation: Biology Department, Woods Hole Oceanographic Institution , Woods Hole, MA , USA.

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.

No MeSH data available.


Comparison with Chthamalus proteus.Midpoint-rooted neighbor-joining topology generated using HKY distances.
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fig-2: Comparison with Chthamalus proteus.Midpoint-rooted neighbor-joining topology generated using HKY distances.

Mentions: For all sites, haplotype diversity was high and Tajima’s D and Fu’s Fs were negative (Table 1), which may indicate population expansion or purifying selection. However, there were no trends with latitude and none of the Tajima’s D values were significant. FST and AMOVA results showed significant genetic structure particularly between distant sites (Table 2), with ∼14% of the variation among populations and ∼86% of the variation within populations (Table 3). The best-fit model selected using the AICc was HKY + I + G. A Bayesian analysis conducted with this model revealed three distinct, well-supported haplogroups (i.e., clades) (Fig. 1). A neighbor-joining tree based on HKY distances also uncovered these three haplogroups (Fig. 1), and was used to assess the distinctiveness of the haplogroups with the Species Delimitation Plugin in Geneious (Rosenberg, 2007; Masters, Fan & Ross, 2011). Within each of the three haplogroups, intraclade distances were significantly smaller than interclade distances (Table 4). Rosenberg’s PAB was 6.5E-18, 6.5E-18, 8.0E-34, for clades 1, 2, and 3, respectively (Table 4), strongly supporting reciprocal monophyly of the three haplogroups. All three haplogroups are clearly differentiated from the sister taxon Chthamalus proteus (Fig. 2).


Phylogeographic structure and northward range expansion in the barnacle Chthamalus fragilis.

Govindarajan AF, Bukša F, Bockrath K, Wares JP, Pineda J - PeerJ (2015)

Comparison with Chthamalus proteus.Midpoint-rooted neighbor-joining topology generated using HKY distances.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4419548&req=5

fig-2: Comparison with Chthamalus proteus.Midpoint-rooted neighbor-joining topology generated using HKY distances.
Mentions: For all sites, haplotype diversity was high and Tajima’s D and Fu’s Fs were negative (Table 1), which may indicate population expansion or purifying selection. However, there were no trends with latitude and none of the Tajima’s D values were significant. FST and AMOVA results showed significant genetic structure particularly between distant sites (Table 2), with ∼14% of the variation among populations and ∼86% of the variation within populations (Table 3). The best-fit model selected using the AICc was HKY + I + G. A Bayesian analysis conducted with this model revealed three distinct, well-supported haplogroups (i.e., clades) (Fig. 1). A neighbor-joining tree based on HKY distances also uncovered these three haplogroups (Fig. 1), and was used to assess the distinctiveness of the haplogroups with the Species Delimitation Plugin in Geneious (Rosenberg, 2007; Masters, Fan & Ross, 2011). Within each of the three haplogroups, intraclade distances were significantly smaller than interclade distances (Table 4). Rosenberg’s PAB was 6.5E-18, 6.5E-18, 8.0E-34, for clades 1, 2, and 3, respectively (Table 4), strongly supporting reciprocal monophyly of the three haplogroups. All three haplogroups are clearly differentiated from the sister taxon Chthamalus proteus (Fig. 2).

Bottom Line: The barnacle Chthamalus fragilis is found along the US Atlantic seaboard historically from the Chesapeake Bay southward, and in the Gulf of Mexico.We found significant genetic structure between northern and southern populations.While the distances between clades do not suggest cryptic speciation, selection and dispersal barriers may be driving the observed structure.

View Article: PubMed Central - HTML - PubMed

Affiliation: Biology Department, Woods Hole Oceanographic Institution , Woods Hole, MA , USA.

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.

No MeSH data available.