Extending over 400 km along the Balcones fault zone, the Edwards Aquifer (EA) in Texas, USA, supports tremendous biodiversity, serving as habitat for >55 described subterranean-adapted aquatic species. Despite hydrologic connectivity throughout the aquifer, certain stygobitic animals persist in narrowly endemic populations. One such stygobiont is the Texas Troglobitic Water Slater; Lirceolus smithii. L. smithii is known only from San Marcos Springs and a nearby flowing artesian well, but congeneric species are found throughout much of the EA. To further our understanding of L.smithii’s ecology, we assessed patterns of geographic, morphological and genetic diversity within L. smithii and among its congeners. Our objectives were: 1) To search and sample groundwater sites within and adjacent to L. smithii’s known range. 2) Develop a morphological key to distinguish cryptic EA Lirceolus species, supported by molecular data. 3) Quantify genetic differentiation within L. smithii and among three other described congeners from the EA. We performed high-frequency aquifer sampling and searched archival collections to assess morphological diversity. To estimate population structure of Lirceolus isopods in the EA, we extracted DNA from individuals captured at targeted EA sites. We then generated genotyping-by-sequencing data to calculate genetic differentiation using the hierarchal Bayesian clustering algorithm program ENTROPY.
Results/Conclusions
Surveying sites for the presence of L. smithii revealed no new localities, but we gained significant insight into the ecology, morphology, and genetic differentiation of Lirceolus in the EA. We successfully developed a dichotomous key for EA Lirceolus species which is supported by our preliminary molecular data. Additionally, this molecular data suggests that L. smithii is highly differentiated from the other Lirceolus species in the EA. Another significant finding from our sampling efforts was the discovery of sympatry between L. smithii and L. pilus and L. hardeni, previously undetected due to cryptic morphology and sampling bias. L. smithii has been petitioned for federal endangered species listing, for its limited range and sensitivity to reduced spring flows and declining water quality caused by a changing climate and anthropogenic impacts in a rapidly growing region where >2 million people are dependent on groundwater. This research contributes to the understanding of the ecology and evolution of subterranean-adapted organisms in karst aquifers, and will serve to aide conservation management decisions to properly protect freshwater resources and EA endemic species.