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Phylogeographic Patterns of the Intertidal Isopods Excirolana braziliensis and Excirolana mayana (Isopoda: Cirolanidae)
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Cryptic species complexes are common in many marine groups. Recent phylogeographic studies in the megadiverse Gulf of California basin have found high levels of cryptic allopatric genetic differentiation in supralittoral isopods. Long standing isolation among populations of these isopods appears to stem from biological characteristics that severely limit their dispersal potential, such as direct development (i.e., lacking a larval stage), as well as a strong association to specific intertidal patchy habitats. Studies of other intertidal isopods have the potential to reveal high levels of cryptic allopatric genetic differentiation. This study examined phylogeographic patterns of intertidal isopods of the genus Excirolana distributed in the Gulf of California. Adults of these isopods are distributed at the highest tidal levels, and phylogeographic studies of Excirolana in Panama and Chile have shown restricted gene flow among populations separated by relatively short distances. Excirolana samples were collected across the Gulf of California, as well as from the Atlantic and Pacific coasts of South and Central America, and from several Caribbean islands; encompassing most of the geographic range for the Excirolana species reported in the Gulf of California. Sequences of DNA fragments from four mitochondrial genes were obtained, and phylogenetic analyses with Maximum Likelihood and Bayesian methods were conducted. Diagnostic morphological characteristics were examined to determine whether individuals corresponded with any of the three species reported in the Gulf of California: E. braziliensis; E. mayana; and E. chamensis. Isopods with morphological characteristics of E. braziliensis and E. mayana were found. In general, relatively low genetic diversity was observed within localities. Phylogenetic analyses indicate that samples with the morphology of E. braziliensis formed a well-supported clade, whereas individuals with the E. mayana morphology formed another well-supported clade. Highly divergent lineages were observed within each of these clades, suggesting they represent cryptic species complexes. In the Gulf of California, several regional clades and subclades of Excirolana exhibit similar distributions to those of several clades within the supralittoral isopods Ligia and Tylos. This study allows a better understanding on the phylogenetic relationships, phylogeographic patterns, and diversity of Excirolana in the Gulf of California, and the Americas in general.
Liu, Shuang (2013). Phylogeographic Patterns of the Intertidal Isopods Excirolana braziliensis and Excirolana mayana (Isopoda: Cirolanidae). Master's thesis, Texas A&M University. Available electronically from