Ecological physiology of the larvel brine fly Ephydra (Hydropyrus) hians, and alkaline-salt lake inhabiting Ephyrid (Diptera) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/c247dw04f

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  • Dipterans of the family Ephydridae (shore and brine flies) are well known for their ability to tolerate and thrive in a wide variety of physically harsh circumstances. The immature stages of one such species of this family, Ephydra hians, are characteristically limited in distribution as benthic inhabitants of highly alkaline salt lakes in the arid regions of western North America. In order to examine the nature of this habitat specificity, the intraspecific comparative physiology of osmotic and ionic regulation, energy metabolism and survival was examined in two populations of brine fly larvae which differ in the historical-environmental stability of their native habitats. The population at Mono Lake, California, has, until recent times, been evolving under relatively stable conditions of water chemistry and habitat availability (i.e., little fluctuation in salinity or littoral benthic habitat due to stable lake level). Since 1940 however, the lake level has been steadily dropping and the dissolved salt content increasing due to diversion of tributary water. The population at Abert Lake, Oregon, has by contrast been subject to severe short-term changes in salinity and habitat availability throughout its history. Larvae were exposed to both alkaline and non-alkaline brines. While both populations displayed hyposmotic regulation in alkaline salt media, Mono Lake larvae consistently showed more effective maintenance of homeostasis. However, in non-alkaline salt water, Mono Lake larvae show poor ability to acclimate to these conditions while Abert Lake larvae are capable of limited physiological adaptation. The general pattern of response to increased salinity or "foreign" water chemistry seems to be an attempt to physiologically accommodate on the part of Abert larvae while Mono larvae become behaviorally and metabolically inactive. The results indicate a physiological basis for biogeogrphic restriction, with the degree of specificity and efficiency of physiological adjustment in this species being apparently related to the historical experience of the particular population. In high salinities of their native lake water, the poor survival and reduced developmental/physiological activity of Mono Lake larvae suggest that a reduction in abundance is likely to accompany further increases in the salinity of the lake.
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