Date of Award
Master of Science (MS)
At least one species of siren is endemic to the Rio Grande Valley of Texas, yet very little is known about the populations of the region. Texas Parks and Wildlife refers to the populations of Siren spp. in South Texas as the “South Texas siren (large form Siren sp. 1),” and recognizes these populations as a threatened species, yet their current population status remains unclear. The species identification of the South Texas siren has been hampered by similarity in morphology across species, and by the lack of complete siren genetic sequences in the NCBI GenBank database. In addition to species ambiguity, very little is known about the preferred habitat characteristics of sirens, specifically in South Texas. The aim of this study was to identify the species of Siren spp. that inhabit South Texas, and to assess the vegetation and environmental variables of siren habitat. Sirens were collected from seventeen water bodies throughout South Texas. Thirty-six sites were assessed for siren presence and correlation with environmental variables, cooccurring species, and vegetation composition. There was no significant correlation between siren presence and the environmental factors; however, nearly all sirens were collected in water bodies that had a high (>95%) percent cover of edge vegetation, and siren abundance appeared to be affected by seasonality. A total of 65 South Texas siren tissue samples were collected between 2013 and 2015. Confirmed specimens of Siren lacertina were compared with the South Texas siren samples, to analyze both coding and non-coding regions (protein coding genes, rRNAs, and tRNAs). For species identification, nine complete mitochondrial genomes were sequenced, and comparisons were made against single genes to assess their utility for species resolution. Sequence divergence and phylogenetic relationships suggest that siren populations in South Texas are composed of at least one distinct species that differs from published sequences for Siren intermedia and S. lacertina. In addition, the results suggest that CO1 is likely the most useful gene for species identification in lieu of the complete mitochondrial genome. The results from this study will provide critical information for this cryptic species, and will aid in the development of future conservation and management practices.
University of Texas Brownsville