Complex Diversity in Stygobromus Amphipods of the Texas Edwards Plateau




Ethridge, Joshua Z.

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Troglomorphic, spring-associated cave amphipods (genus Stygobromus) occupy discontinuous localities m the Edwards plateau region of the south-central United States. Given the prevalence of subterranean cryptic species diversity among widely disparate animal taxa and general patterns of subterranean dispersal and vicariance, Stygobromus may contain undetected biodiversity at the species and population levels, with conservation implications for S. peckz, a federal and state of Texas endangered short-range endemic. To explore Stygobromus evolutionary history, mitochondrial sequence (COI), nuclear sequence (ITS1), and AFLP data were collected for S. peckz and Edwards plateau congeners. The morphology-based taxonomy and proposed phylogeny of Stygobromus species and species groups were treated as hypotheses and tested with molecular data. Stygobromus peckz, which emerges from multiple spring flows at Landa Lake, was examined with population genetics tools to characterize population structure and diversity, with diversity measures compared to congeners and previous findings for another spring endemic, the federally endangered Comal Springs riffle beetle, Heterelms comalensus, which shares habitat with S. peckt. The taxonomy of Stygobromus species and species groups conflicted with molecular phylogenetic data and there is strong evidence of significant cryptic diversity. Within S. peckz, COI data contained two significantly diverged clades that may reflect a history of isolation succeeded by current sympatry and admixture. S. pecki genetic diversity was similar to that for congeners and significantly greater than for H. comalensis. This study demonstrates that Edwards plateau Stygobromus are a complex and genetically diverse group with substantially more diversity than currently recognized.



Amphipoda, Freshwater invertebrates, Cave animals, Evolution, Edwards Plateau


Ethridge, J. Z. (2011). <i>Complex diversity in Stygobromus amphipods of the Texas Edwards Plateau</i> (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.


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