These results as well as molecular divergence data are consistent with the hypothesis that members of this genus were isolated in springs during a post-Cretaceous oceanic recession toward what is now the Gulf of Mexico. Protein and DNA sequence analyses to identify degrees of population differentiation among Big Bend T. subequalum subpopulations are currently underway. To investigate genetic and morphological variation in populations of Thermosphaeroma isopods inhabiting thermal springs in Big Bend National Park and the Lower Canyons of the Rio Grande River. Our goal is to determine the relationship of these populations to other known populations of Thermosphaeroma isopods. Morphological investigation of male and female genitalia using scanning EM is currently underway.
Genetic investigations are also underway and preliminary results are as follows.
Thermosphaeroma populations are found in nine hot springs located on both sides of the Rio Grande River over approximately 90 miles. To determine if these populations are isolated within the hot springs or represent one continuous population, we examined genetic variation at 9 allozyme loci using starch gel electrophoresis. Our calculated mean FST value of 0.1032 reveals moderate genetic differentiation. These results indicate that significant population structure does exist among the nine T. subequalum populations.