textAbstract: The use of aquifer-dwelling organisms (stygobites) for
learning about past and present subterranean hydrologic connections was
evaluated in the Edwards (Balcones Fault Zone), Trinity, and EdwardsTrinity
(Plateau) aquifers of Texas and adjacent areas in north Mexico, an
area with complex karst groundwater flow and sociopolitical problems
stemming from overuse and contamination. A priori predictions of
subterranean hydrogeologic history were made based on a literature
review, and these predictions were compared to phylogenies of two
aquifer dwelling isopods created based on mitochondrial gene sequences
(16S ribosomal RNA and cytochrome c oxidase subunit I). Using
likelihood and parsimony-based comparisons, Cirolanides (Isopoda:
Cirolanidae) was found to have a phylogenetic history congruent with a
priori predictions of subterranean hydrogeologic history in its terminal
nodes. Conversely, basal branches of the phylogenetic tree had
placement that was not predicted by this history, a phenomenon that may
be indicative of a lack of understanding of subterranean hydrogeology of
the area. Lirceolus (Isopoda: Asellidae) had a phylogenetic history
congruent with an alternative hypothesis of water flow, namely the
patterns of surface drainages. This difference of patterns for two species
that both live in the aquifer is probably related to their ecology and
evolutionary history, with Cirolanides having invaded the cave habitat as a
single marine population and Lirceolus invading the cave habitat as a
freshwater migrant with possible pre-existing genetic structure determined
by surface drainages. This study pioneers testing of a priori
biogeographic hypotheses using phylogenies of aquifer organisms and the
creation of hydrogeologic histories in a karst setting, and supports the use
of these methods to aid in understanding biogeography and aquifer
evolution.Biological Sciences, School o