The Massasauga (Sistrurus catenatus) consists of three subspecies: the Eastern (S. c. catenatus), Western (S. c. tergeminus), and Desert Massasaugas (S. c. edwardsii). Relationships among these subspecies pose challenges for conservation and management in Texas where both Western and Desert Massasauga subspecies occur. The Western Massasauga has no special state or federal status, while the Desert Massasagua has been petitioned for federal listing under the U.S. Endangered Species Act.
In 2012, to better define the status of Massasauga subspecies in Texas, the Nongame and Rare Species Program at Texas Parks and Wildlife Department funded a genetic study conducted by researchers with the Institute of Renewable Natural Resources at Texas A&M University. This work was made possible through TPWD’s State Wildlife Grant Program. Ryberg et al. (2013) used nuclear and mitochondrial DNA variation to define the geographic relationships between Western and Desert Massasaugas in Texas and adjacent states. The researchers also assessed baseline population structure throughout the state and discussed the establishment of potential management units for Desert Massasauga should listing occur.
They found strong evidence that the Western and Desert Massasaugas are genetically indistinguishable for the genes investigated. Within the Western-Desert Massasauga group, they found some evidence of population structure among five population segments. These five distinct population segments could be considered for listing, but with no clear evidence suggesting relationships among these disjunct populations, they recommend that more research using other molecular markers be conducted to provide a measure of genetic connectivity capable of revealing more detailed taxonomic and population level structure for identifying potential conservation units.
Regardless of federal ruling, the overall rarity of Massasaugas in south Texas and their geographic isolation from other populations in the Western-Desert Massassauga group means that they deserve continued attention. The researchers recommend continued survey efforts in this region to provide information on the distribution and abundance of this Massasauga population and to monitor changes to its habitat over time.
Ryberg, W.A., A. Blick, J.A. Harvey, T.J. Hibbitts, and G. Voelker. 2013. Genetic determination of the Desert Massassauga distribution in Texas. State Wildlife Grant Report to Texas Parks and Wildlife Department.