Osmoregulation in an Alkaline Salt Lake Insect, Ephydra (hydropyrus) Hians Say (diptera: Ephydridae) in Relation to Water Chemistry

Larvae of the alkali fly Ephydra hians, from Mono Lake (California), were exposed to osmotic concentrations ranging from distilled water to over 6000 mOsm of either alkaline Mono Lake water, or non-alkaline sea water/sodium chloride solutions. Larvae were capable of both hyperand hypo-osmotic regulation of haemolymph osmolality (at around 300mOsm) in Mono Lake water, but this ability was less effective in sea water/sodium chloride. In addition, higher mortality rates in sea water/sodium chloride suggest larvae are less tolerant of this chloride-dominated water chemistry. Pm-acclimation of larvae in sea water/sodium chloride did not improve survival in higher concentrations of this solution relative to larvae acclimated to Mono Lake water. At and above 200 g/l total dissolved solids (about 4800 mOsm) of Mono Lake water, larval survival is severely reduced, in association with osmotic dehydration. Sodium and chloride are the major haemolymph osmolytes, comprising about 70% of the total osmotic concentration. The results suggest that this species is alkali-adapted, and that restriction in habitat distribution from non-alkaline chloride waters and salinities above 200 g/l has a physiological basis. Key Word Index: Osmoregulation, Ephydridae, saline lake, Mono Lake, Ephydra