No Evidence for Temporal Variation in a Cryptic Species Community of Freshwater Amphipods of the Hyalella azteca Species Complex

The co-occurrence of cryptic species of Hyalella amphipods is a challenge to our traditional views of how species assemble. Since these species have similar morphologies, it is not evident that they have developed phenotypic differences that would allow them to occupy different ecological niches. We examined the structure of a community of Hyalella amphipods in the littoral zone of a boreal lake to verify if temporal variation was present in relative abundances. Morphological and molecular analyses using the mitochondrial cytochrome c oxidase I (COI) gene enabled us to detect three cryptic species at the study site. No temporal variation was observed in the community, as one cryptic species was always more abundant than the two others. The relative abundances of each species in the community appeared constant at least for the open-water season, both for adult and juvenile amphipods. Niche differences are still to be found among these species, but it is suggested that migration from nearby sites may be an important factor explaining the species co-occurrence. OPEN ACCESS Diversity 2011, 3 391