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Phylogeography of five species of the stygobitic shrimp genus Typhlatya, as determined from the sequence analysis of three mitochondrial genes
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Classical taxonomic studies of stygobitic (aquatic cave-limited) species have concentrated primarily on their unique morphological characters, many of which may be the result of convergent or parallel evolution, rather than their true phylogenetic affinities. In this study, three mitochondrial genes, 16S rRNA, cytochrome oxidase subunit I and cytochrome b, were sequenced in order to make interspecific comparisons among five species of the stygobitic atyid shrimp genus, Typhlatya. Phylogenetic analyses using parsimony and neighbor-joining were used to determine what phylogenetic relationships exist between disjunct insular versus continental and marine versus freshwater species within the genus and to test the monophyletic origin of these species. The individual and combined analyses of the three mitochondrial genes yielded support for a monophyletic origin of the five species within the genus Typhlatya relative to its sister taxa Antecaridina lauensis. In the majority of phylogenies created, two distinct clades were present. The first clade, the insular marine clade, grouped together Typhlatya garciai and T. iliffei, both which inhabit brackish to marine waters in caves on small islands in the Atlantic Ocean. The second clade, the continental freshwater clade, grouped T. mitchelli, T. pearsei and T. sp which inhabit freshwaters in caves of the northernmost regions of the Yucatan Peninsula of Mexico. These groupings indicate that two independent and separate speciation events have occurred since the most recent common ancestor of the five species. One speciation event led to the colonization of the Yucatan Peninsula, probably from an epigean marine ancestor as it has been proposed that all atyids have a marine origin, and a second which led to the colonization of the insular habitats, Bermuda and the Caicos Islands. It was estimated from the cytochrome b gene that the insular species last shared a common ancestor with the three Yucatan species around 7.5 mya. Subsequently, the two insular species diverged approximately 6 mya, while T. pearsei diverged from the Yucatan ancestor around 7 mya and T. mitchelli and T. sp. then split from each other around 3.6 mya.
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Includes bibliographical references (leaves 49-57).
Issued also on microfiche from Lange Micrographics.
Belcher, Rebecca Lane (2004). Phylogeography of five species of the stygobitic shrimp genus Typhlatya, as determined from the sequence analysis of three mitochondrial genes. Master's thesis, Texas A&M University. Available electronically from
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