Phylogeny and Size Differentially Influence Dissolved Cd and Zn Bioaccumulation Parameters among Closely Related Aquatic Insects

Evolutionarily distinct lineages can vary markedly in their accumulation of, and sensitivity to, contaminants. However, less is known about variability among closely related species. Here, we compared dissolved Cd and Zn bioaccumulation in 19 species spanning two species-rich aquatic insect families: Ephemerellidae (order Ephemeroptera (mayflies)), generalized to be metal sensitive, and Hydropsychidae (order Trichoptera (caddisflies)), generalized to be metal tolerant. Across all species, Zn and Cd uptake rate constants (k(u)s), efflux rate constants (k(e)s) and bioconcentration factors (BCFs) strongly covaried, suggesting that these metals share transport pathways in these distinct lineages. K(u)s and BCFs were substantially larger in Ephemerellidae than in Hydropsychidae, whereas k(e)s did not dramatically differ between the two families. Body size played an important role in driving k(u) differences among species, but had no influence on k(e)s. While familial differences in metal bioconcentration were striking, each family exhibited tremendous variability in all bioaccumulation parameters. At finer levels of taxonomic resolution (within families), phylogeny did not account for differences in metal bioaccumulation. These findings suggest that intrafamily variability can be profound and have important practical implications in that we need to better understand how well surrogate species represent their fellow congeners and family members.