Genetic structure of Gammarus fossarum populations

Abstract

The population structure of Gammarus fossarum Koch was analysed at six enzyme loci in 38 populations from the Danube and Rhine drainage system in the southern part of Germany. The species-restricted distribution to the upper reaches of rivers was reflected in the large genetic differentiation of all populations. The genetic pattern can be explained as a dynamic balance between genetic drift and restricted gene flow. As migration mainly occurs along the rivers, a treelike pattern showing the genetic relationship of the populations corresponded well with the geographical position of the populations in the river system. The overall gene flow was estimated as low, although small rivers have a higher migration rate than large rivers. The watershed between the Rhine and Danube drainage basins affects gene flow at about the same level as the major migration barriers within the Danube drainage basin.Each sampled population seemed to be panmictic with respect to the variation at single loci. In two-locus analyses, linkage disequilibria were found in several populations at combinations of three of the loci. A probable cause is that the linkage disequilibria are produced through random genetic drift (possibly through bottlenecks) and that the three loci are so closely linked that the recombination rate is too low to establish linkage equilibrium.

Taxonomic Status and Phylogenetic Relationships of Some Species of the GenusGammarus(Crustacea, Amphipoda) Deduced from Mitochondrial DNA Sequences

“…The apparent lack of gene flow among most of gammarid populations may reflect their degree of geographic isolation. This was previously observed through allozyme studies for populations of G. fossarum from the Danube and Rhine drainage systems (Siegismund and Mü ller, 1991) and is also true for the closely spaced populations of G. fossarum in the Grenoble region, for which mtDNA polymorphism is further investigated elsewhere (Meyran and Taberlet, 1996a).…”

“…Geographic variation among local populations also occurs genetically, as previously observed for some species after isozyme analysis (reviewed in Siegismund and Mü ller, 1991). However, data on interregional intraspecific variation using such classical discriminating tools have encouraged the recognition of subspecies or sibling species, which may be a source of taxonomic confusion between ''classical species'' and ''deviating forms'' (Scheepmaker, 1990).…”

“…Allozyme frequency data from selected loci have made possible the examination of patterns of genetic variation among different species (Bulnheim and Scholl, 1981;Siegismund, 1988;Yampolsky et al, 1994) and among different populations of a given species (Gooch and Hetrich, 1979;Bulnheim, 1985;Siegismund and Mü ller, 1991;Kane et al, 1992;Patarnello et al, 1992;Mü ller et al, 1995) but have led to fragmentary results that are incomplete for addressing phylogenetics in Gammarus (Scheepmaker, 1990). However, in some populations, the species identification appears so complicated that the simultaneous use of the classical criteria previously described has failed to clarify the situation (Scheepmaker, 1987).…”

Hidden Biodiversity in an Ecologically Important Freshwater Amphipod: Differences in Genetic Structure between Two Cryptic Species

“…fish, [10], [11]), and intermediate hosts for parasites [12]. Multiple studies have shown high levels of population differentiation [13] as well as the evolution of reproductively isolated cryptic species [14]–[16] within morphological species. The fact that such pronounced genetic structure arises despite frequently observed large population sizes with hundreds to thousands of individuals per m 2 [17]–[19] suggests substantial limitations of gene flow between populations.…”

“…Several population genetic studies have been conducted on G. fossarum , but often focused on limited geographical regions containing only one of the cryptic species and/or were constrained by the limited availability of highly variable and selectively neutral markers [13], [14], [35], [38]–[40]. We here make use of nine recently developed microsatellite markers [41] to examine the intraspecific genetic structure within two cryptic species and potential differences between them.…”