Abstract
Phylogeographic studies have provided valuable insights into the evolutionary histories and biodiversity of different groups in the Caribbean, a region that harbors exceptional terrestrial and marine biodiversity. Herein, we examined phylogeographic patterns of the poorly dispersing supralittoral isopod Ligia sampled from 35 localities in the Caribbean Sea and adjacent areas, as well as from Veracruz (Gulf of Mexico), the type locality of L. baudiniana (the only currently recognized native Ligia species in the Caribbean). We conducted Maximum Likelihood and Bayesian phylogenetic analyses of four mitochondrial genes (Cytb, 16S rDNA, 12S rDNA and COI) and Parsimony analyses of one nuclear gene (NaK). We found a well-supported and highly divergent clade of Ligia that is distributed in the Caribbean Sea, Bahamas, southern Florida, Bermuda, and the Pacific coast of Central America and Colombia, but not in the Gulf of Mexico. A characteristic appendix masculina distinguishes this clade from other lineages of Ligia. Large divergences within this clade suggest that it constitutes a cryptic species complex. Genetically and morphologically, the specimens from the type locality of L. baudiniana were indistinguishable from the non-native species L. exotica. Some phylogeographic patterns of Ligia in the study area may be consistent with the proto-Antillean or GAARlandia vicariant hypotheses, but uncertainty concerning divergence times and aspects of the geological history precludes stronger biogeographical inferences. Passive overwater dispersal appears to have played an important role in shaping phylogeographic patterns of Ligia in the Caribbean Sea. These patterns, however, do not correspond with predicted biogeographic patterns based on population connectivity of marine organisms with larval dispersal, and do not reflect the southeast to northwest colonization pattern that has been proposed for the colonization of the Caribbean from South America by some terrestrial animals.
Highlights
The Caribbean Sea region has served as an incubator for an exceptionally diverse terrestrial and marine biota; the most diverse of the Atlantic Basin (Myers et al, 2000; Roberts et al, 2002; Brummitt and Lughadha, 2003; Kerswell, 2006; Miloslavich et al, 2010)
The external morphology of the appendix masculina enabled distinction of the Study Area Clade from other lacking for another supralittoral isopod genus (Ligia) specimens examined by us and reported in the literature (Schultz, 1972; Schultz and Johnson, 1984; Lee, 1994; Taiti et al, 2003; KhalajiPirbalouty and Wägele, 2010), but not from specimens assigned to L. baudiniana by Schultz (1972) and Schultz and Johnson (1984) from Florida and Bermuda; localities that fall within our Study Area
It is possible that L. baudiniana was described on the basis of L. exotica individuals, rendering L. baudiniana a junior synonym of L. exotica (Roux, 1828), a proposal that was put forth by Budde-Lund (1885)
Summary
The Caribbean Sea region has served as an incubator for an exceptionally diverse terrestrial and marine biota; the most diverse of the Atlantic Basin (Myers et al, 2000; Roberts et al, 2002; Brummitt and Lughadha, 2003; Kerswell, 2006; Miloslavich et al, 2010). Striking radiations observed in poorly dispersing endemics, such as the Caribbean Anolis lizards, a classic case of adaptive radiation (Losos, 2009), and enduring controversies concerning the contributions of vicariance and over-water dispersal to shaping the region’s terrestrial biodiversity (Barbour, 1914; Myers, 1937; Darlington, 1938; Savage, 1982; Briggs, 1984; Williams, 1989; Hedges et al, 1992; Crother and Guyer, 1996; Guyer and Crother, 1996; Hedges, 1996a), have stimulated phylogeographic research in the Caribbean These studies have uncovered a large amount of cryptic biodiversity and enhanced our understanding on diversification processes in the Caribbean, but have been strongly biased toward terrestrial vertebrates (Hower and Hedges, 2003; Dávalos, 2004, 2007; Hedges, 2006; Heinicke et al, 2007; Alonso et al, 2012), compared to terrestrial invertebrates (Crews and Gillespie, 2010; Oneal et al, 2010). The supralittoral and high intertidal, at the transition between sea and land, are inhabited by poorly studied taxa that have the potential of revealing high levels of unknown biodiversity and phylogeographic structure
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