Abstract

The recent development of DNA-based species classification methods has led to the revision of many morphology-based species designations as genetic data has provided new information for species delineation. Analysis of standardized DNA ‘barcoding’ gene regions has proven particularly effective in resolving the taxonomic status of taxa that display phenotypic and habitat overlap.

Freshwater Unionid and Margaritiferid mussels comprise one of the most diverse aquatic taxa in North America, but are also among the most threatened, with over 70% of the approximately 300 native species considered at-risk or in decline. Although mussels face extensive threats from anthropogenic activity, conservation efforts have been hampered by limited knowledge of mussel ecology, their uncertain phylogeny and species status, and difficulty of identification. Within East Texas, six of the 37 native mussel species are listed as threatened and three are under consideration for federal Endangered Species Act listing. In this study, a phylogenetic analysis was performed on three mitochondrial genes to examine the occurrence and phylogeny of four Unionid mussel species, the Texas Pigtoe, Fusconaia askewi (Marsh 1896); Triangle Pigtoe, Fusconaia lananensis (Frierson 1901); Wabash Pigtoe, Fusconaia flava (Rafinesque 1820); and Louisiana Pigtoe, Pleurobema riddellii (Lea 1861), using an expanded sample dataset including the majority of these species’ known occurrence in Texas. As all of these mussels except F. flava are listed as threatened by the state of Texas, and both F. lananensis and P. riddellii are under consideration for federal Endangered Species Act listing, revisions to the taxonomy of this group will have important implications for future conservation planning.

Phylogenetic analysis found three monophyletic clades consisting of F. flava, P. riddellii, and intermixed F. askewi and F. lananensis. Phylogenetic analysis and comparative divergence measures identified F. askewi and F. lananensis as a single monophyletic clade, with F. flava and P. riddellii supported as separate monophyletic lineages.

The high degree of observed morphological and habitat similarity and lack of genetic divergence from the Texas Pigtoe, Fusconaia askewi, suggests that the Triangle Pigtoe, Fusconaia lananensis, is not a valid species and that individuals and populations classified as F. lananensis should be considered as belonging to F. askewi. Additionally, specimens identified as F. flava matched existing F. flava sequences accessed from Genbank, suggesting that reported species occurrences from these locations are valid.

Date of publication

Summer 8-14-2017

Document Type

Thesis

Language

english

Persistent identifier

http://hdl.handle.net/10950/589

Committee members

Dr. Srini Kambhapati, Dr. Neil Ford, Dr. Lance Williams

Degree

Master of Science in Biology

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