Genetic evidence for a Hyalella species complex within the Great Lakes - St. Lawrence River drainage basin: implications for ecotoxicology and conservation biology

We examined the population genetic structure (allozyme variation) of Hyalella azteca (Saussure) (Amphipoda:Crustacea) collected from six field locations and one laboratory culture within and near the Great Lakes – St. Lawrence Riverdrainage basin. We found considerable variability in allele frequency among locations. Wright’s FST value averaged over 10polymorphic allozyme loci was 0.56 (range 0.10–0.93), indicating “very great” levels of genetic differentiation amonglocations. Analyses of genetic distance (Nei’s, Rogers’) suggested the presence of four genetically distinct groups. For thelaboratory population, differences were of sufficient magnitude to merit consideration as a separate (presently undescribed)species of Hyalella, showing fixed differences at 2 of 10 loci examined. The presence of genetically distinctspecies/populations within H.azteca potentially confounds the results of laboratory ecotoxicology tests, depending on whichindividuals are used in an analysis. Accordingly, we urge caution where results may be used to establish water-quality criteria.From a conservation perspective, the presence of an undescribed species within a relatively well known taxon such as H.aztecasuggests that current taxonomic inventories of benthic invertebrates may not only be incomplete, but perhaps grosslyunderestimated. We advocate a taxonomic reevaluation of H azteca and other widespread benthic taxa, with particular