Genetic Evaluation of Sirens in Texas

Sirens have always been a taxonomically controversial group. Historically, morphological characters were used to delineate taxonomic groups. However, the neotenic characters seen in sirens complicate taxonomic assignment. While it has been traditionally thought that only lesser sirens (Siren intermedia) resided in Texas, it has been well known that sirens in southern Texas are morphologically divergent from typical lesser sirens. The taxonomic classification of these sirens in southern Texas has been long debated and currently remains in question. The sirens in eastern Texas, however, are not morphologically divergent from that of typical lesser sirens, leaving us to wonder where in Texas these two groups meet and how their evolutionary relationship may help define the taxonomic identity of southern Texas sirens. It is important that we answer this question since sirens in some parts of southern Texas have been classified as state-threatened and protection of an undefined taxon is problematic. Since morphological identification has been challenging, I approached this issue using modern molecular phylogenetics. I sequenced 4 mitochondrial genes (CO1, ND2, 16S, and ND5) from samples of both southern Texas and eastern Texas sirens, as well as sirens from out of state. Using those sequences and other siren sequences published online, I created phylogenic trees, using maximum likelihood and Bayesian analyses, and haplotype networks. These analyses revealed that, of the 4 genes sequenced, there were conflicting results, with CO1 and ND2 representing one relationship and 16S and ND5 representing another. When concatenated, the maximum likelihood and Bayesian analyses of the sequences sided with the latter 2 genes, suggesting that eastern Texas sirens belong to a clade nested within the southern Texas sirens. Despite the conflicts, there was a consensus among the results in that the sirens of southern Texas seem to relate closer to lesser sirens than greater sirens or reticulated sirens. As such, there does not seem to be a significant difference between sirens within southern Texas, but sirens in eastern and southern Texas were somewhat divergent from each other. While the scope of this project is too small to definitively determine the exact relationship between these Texas sirens, my data strongly supports the sirens of southern Texas are lesser sirens.