Great Basin Naturalist


Four species of the genus Ephydra are commonly found in saline waters within the hydrologic Great Basin: E. hians, E. gracilis, E. packardi, and E. auripes. Though none of these brine flies is endemic (distributions also occur outside the Great Basin), they all inhabit distinctive habitat types and form the characteristic benthic insect fauna of inland saline-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 may impose physiological or ecological constraints and 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, based on limited habitat data, 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 accomplished by swift adult colonizing ability and rapid larval development rates.

It is hypothesized that adaptive specializations in both 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.