Experimental Populations of Gammarus duebeni in Fresh Water with a Low Sodium Content

Abstract

THE amphipod Gammarus duebeni Liljeborg is a common member of the fauna of salt-marshes and estuaries; it also occupies fresh water in coastal areas in north-west Europe^1,2. Reid³ and Beadle and Cragg⁴ postulated the existence of physiological races to explain the presence of G. duebeni in fresh water, but Hynes¹ found no evidence in support of this view. Studies^5,6 on sodium regulation in populations of G. duebeni living in brackish and fresh water localities in various parts of the British Isles have shown that the sodium regulatory mechanism exhibits characteristic features which differ in populations living in (a) brackish water, (b) fresh water in western Britain, (c) fresh water in Ireland, and the differences are correlated with the sodium content of the habitat. In order to determine whether the differences between populations are phenotypic or genotypic in origin, a series of experimental populations have been established in fresh water with a very low sodium content.