Genetic differentiation in populations of the freshwater amphipods Gammarus roeseli and Gammarus fossarum

Abstract

The population structures of the two freshwater Gammarus species G. roeseli GERVAIS and G. fossarum KOCH were studied by starch gel electrophoresis. The main study area was the river Isar with its tributaries in Southern Bavaria. The genetic divergence in populations of the two species reflects their geographical distribution pattern. G. roeseli is very common and is continuously distributed in the rivers. This species showed a regular pattern in its genetic variation. The two polymorphic loci found in this species had either a relatively constant frequency in a part of the river system or showed a parallel clinal variation in the Isar river. In contrast, G. fossarum, which has a patchy distribution in the study area and therefore was collected at fewer locations, had a more differentiated population structure. No clinal variation was observed in this species; all populations differed from each other in at least one of the four polymorphic loci. The divergence of the populations is described with a tree of genetic relatedness that corresponds well with the geographic distribution. Copyright © 1988, Wiley Blackwell. All rights reserved