HYDROLOGICAL FRAGMENTATION AND GENETIC ISOLATION OF SPRINGS FOLLOWING TECTONIC EXTENSION IN THE SOUTHERN GREAT BASIN OF NV AND CA

Over 2000 springs emerge in the southern Great Basin encompassing portions of southern NV and CA including Death Valley, one of the most extreme environments on Earth. These springs developed in response to tectonic processes at long timescales and climate variations at shorter timescales. Tectonic extension in the region uplifted and disconnected mountain ranges in the area creating basin and range topography starting about 14 Ma. At about 3 Ma, rapid pull-apart basin extension created the long, narrow valleys oriented north-south bounded by high mountain ranges that are observed today. These tectonic processes affected the climatology of the region, in turn, impacting continental sedimentation, creating the southern Sierra Nevada rain shadow, and modifying the regional hydrological system. Climate variations, namely glacial-interglacial cycles, have been the major driver of hydrological change in the region for the last 500 ka. Surface water drainages and groundwater flowpaths adjusted in response to the changes in topography and climatology. During glacial stands, glaciers advanced in the Sierra Nevada, runoff increased, and the river-lacustrine system became connected. As the glaciers receded and the climate warmed during interglacial stands, the interconnected river-lacustrine system dried leaving behind numerous isolated spring systems. These springs today are biodiversity hotspots. Approximately 250 springs in the study area are known to support more than 40 taxonomically distinct crenobiontic vertebrates and invertebrates and over 500 distinct species of Bacteria and Archaea. Biological markers (mtDNA) indicate that some of the crenobiontic species, pupfish for example, diverged from a genetic ancestor 3 to 2 Ma suggesting that extensional tectonics forced the hydrological isolation and subsequent separate evolutionary pathways of these species. The following presentations will address these questions. How did through-flowing surface-water hydrological systems become transformed into a myriad of tiny aquatic oases that have clearly persisted on the million-year time scale (based on estimated required speciation time)? What was the forcing for, and the history of, this hydrological evolution? How did the aquatic ecosystems and species respond to this fragmentation?