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Show David B. Herbst Sierra Nevada Aquatic Research Laboratory University of California Route 1, Box 198 Mammoth Lakes, CA 93546 Biogeography, Physiology and Ecology of the Brine Fly Genus Ephydra ( Diptera: Ephydridae) in Saline Waters of the Great Basin Four species of the genus Ephydra are found in saline waters within the hydrologic Great Basin - E. hians, E. gracilis, E. packardi, and E. auripes. Though none of these brine flies are endemic ( spp. are found also outside the Great Basin), they form the characteristic insect fauna of saline desert water habitats. The affinities of each species for different salinity levels and chemical compositions, and ephemeral to perennial habitats appear to form the basis for biogeographic distribution patterns. Within any habitat, changing salinity conditions over time further alter patterns of population productivity, and the relative abundance of co- inhabiting species. Based on the physiology of salt tolerance known for these species, high salinity conditions favor E. hians in alkaline water and E. gracilis in chloride water. At lower salinities E. auripes and E. packardi are often more common, again showing respective preferences for alkaline and chloride chemical conditions. Specialized adaptations for alkaline carbonate waters are found in the larval Malpighian tubule lime gland of the alkali fly E. hians, while high salt tolerance in E. gracilis appears to be conferred by high hemolymph osmolality. Adaptation to ephemeral and low salinity conditions may be effected by rapid adult colonizing ability and larval development rates. It is hypothesized that adaptative specializations in physiology and life history, and varied geochemistry of saline water habitats across the Great Basin produce the biogeographic pattern of distributions for species in this genus. This perspective on the genus Ephydra, and possibly other biota of mineral- rich Great Basin waters suggests that interconnections among pluvial lakes may be less relevant to aquatic biogeography than chemical profiles developing in remnant lakes and ponds with the progression of arid post- pluvial climatic conditions. Ecological and physiological limitations under changing salinitiy conditions in salt lakes result in changing distributions and productivity of Ephydra spp. Brine flies play a central trophic role in saline lakes by consuming benthic algae and providing an abundant food source, fed upon extensively by migratory and breeding shorebirds and waterfowl. The historical development of the Pacific Flyway and avian breeding colonies during the Holocene may therefore be closely linked to salinity- related changes in the population ecology and production of Ephydra in different saline lake basins. Experimental microcosm studies provide evidence of changing production dynamics, supporting observations at Mono Lake, Abert Lake and Great Salt Lake over periods of varied lake level and salinity. Predictions yet to be tested include relating geographic distributions to ionic tolerance, colonizing ability, life history traits, and population production in halophilic and thermophilic Ephydra, and within other Ephydridae found in aquatic ecosystems of the Great Basin. |
