Differentiation in morphology and habitat partitioning of genetically characterized Gammarus fossarum forms (Amphipoda) across a contact zone

Evolutionary processes do not affect all character types equally. Depending on environmental effects, morphological and ecological evolution may be uncoupled from molecular evolution. A natural contact zone between two forms of the amphipod Gammarus fossarum was used to assess the levels of differentiation in genetic, morphological and habitat characters. About 50 individuals per population were analysed for six enzyme loci in 72 populations and four size-standardized morphometric traits in a subset of 32 populations. Nine environmental parameters per population were used to characterize the habitat. All three character sets revealed significant divergences between G. fossarum forms. The ea…