Low intraspecific genetic divergence and weak niche differentiation despite wide ranges and extensive sympatry in two epigean Niphargus species (Crustacea: Amphipoda)
Abstract
The amphipod genus Niphargus comprises hundreds of eyeless and depigmented species with narrow ranges in Western Palaearctic subterranean freshwaters. Niphargus hrabei and N. valachicus, two morphologically and ecologically similar species, are atypical due to their epigean lifestyle and large ranges.
Given their wide and largely sympatric distributions, we explored their potential ecological niche overlap by comparing morphological functional traits, patterns of co-occurrence and habitat selection, and tested for cryptic diversity by examining variation of mitochondrial and nuclear markers in selected populations. Mitochondrial sequences and the presence of shared nuclear alleles among individuals collected along the study area did not support the existence of cryptic lineages; two other Niphargus species described in the past from Hungary seem to be their younger synonyms.
Except for body size, both species were morphologically similar and seem only weakly differentiated ecologically. Though smaller in size, N. hrabei is ecologically more tolerant, while N. valachicus might be a superior competitor due to its larger size.
Despite large-scale sympatry, co-occurrence of both species was rare. Their present distributions may result from a dynamic relationship between dispersal ability and competitive strength.
These widespread and euryoecious Niphargus species demonstrate that the genus may be successful not only in the subterranean realm but also in various surface waters.