Placing the Floridian Marine Genetic Disjunction Into a Regional Evolutionary Context Using the Scorched Mussel, Brachidontes Exustus, Species Complex

Abstract

Abstract. The well-documented Floridian Gulf/Atlantic marine genetic disjunction provides an influential example of presumed vicariant cladogenesis along a continental coastline for major elements of a diverse nearshore fauna. However, it is unclear if this disjunction represents a local anomaly for regionally distributed morphospecies, or if it is merely one of many such cryptic phylogenetic splits that underlay their assumed genetic cohesiveness. We aimed to place the previously characterized scorched mussel Gulf/Atlantic genetic disjunction into a regional phylogenetic perspective by incorporating genotypes of nominal conspecifics sampled throughout the Caribbean Basin as well as those of eastern Pacific potential geminate species. Our results show it to be one of multiple latent regional genetic disjunctions, involving five cryptic Caribbean species, that appear to be the product of a long history of regional cladogenesis. Disjunctions involving three stem lineages clearly predate formation of the Isthmus of Panama and of the Caribbean Sea, although four of the five cryptic species have within-basin sister relationships. Surprisingly, the Atlantic clade was also found to be widespread in the southern Caribbean, and ancestral demography calculations through time for Atlantic coast-specific genotypes are consistent with a northward range extension after the last glacial maximum. Our new data seriously undermine the hypothesis of a Floridian vicariant genesis and imply that the scorched mussel Gulf/Atlantic disjunction represents a case of geographic and temporal pseudocongruence. All five Caribbean Basin cryptic species exhibited an intriguing pattern of predominantly allopatric distribution characterized by distinct geographic areas of ecological dominance, often adjoining those of sister taxa. This pattern of distribution is consistent with allopatric speciation origins, coupled with restricted postspeciation range extensions. Several lines of indirect evidence favor the hypothesis that the predominantly allopatric distributions are maintained over evolutionary time scales, primarily by postrecruitment ecological filters rather than by oceanographic barriers to larvalmediated gene flow.

A bio-oceanographic filter to larval dispersal in a reef-building coral

“…However, with the application of higher-resolution microsatellite markers, population structure has been detected in Bahamian populations of brooding gorgonians that can be divided into three subregions (GutierrezRodriguez and Lasker 2004). Similar patterns of genetic breaks have been detected among lineages of a marine mussel (Lee and Foighil 2005).…”

“…Potential mechanisms underlying a barrier to larval dispersal in A. palmata may act before or after larvae recruit (or during both periods). For example, some distinct lineages of a Caribbean mussel are maintained by postrecruitment processes rather than as a result of limited dispersal (Lee and Foighil 2005). This hypothesis is testable with reciprocal transplanting experiments of A. palmata larvae among habitats on either side of the Mona Passage.…”

Worms without borders: genetic diversity patterns in four Brazilian Ototyphlonemertes species (Nemertea, Hoplonemertea)

“…In the marine environment, boundaries within species' distributions may either be generated by (1) hydrodynamic factors limiting recruitment or availability of planktonic larvae (e.g., Gaylord and Gaines 2000;Hohenlohe 2004) or (2) gradients in ecological factors that can impose limit ranges (Lee and O'Foighil 2005;Rocha et al 2005). Few studies of nemerteans have addressed gene flow, but there is evidence of dispersal irrespective of developmental type.…”

Calibrating the chitons (Mollusca: Polyplacophora) molecular clock with the mitochondrial DNA cytochrome C oxidase I gene

“…Among mollusks, the percentage of divergence of COI gene across the Panamic Isthmus has been studied in gastropods sister species (Hellberg 1998, Collin 2003, Latiolais et al 2006, Miura et al 2010, also among bivalves (Marko 2002, Lee & Foighil 2005. However, COI has not been used yet to specifically compare sister species in chitons.…”