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 (<i>k</i>_us), efflux rate constants (<i>k</i>_es) and bioconcentration factors (BCFs) strongly covaried, suggesting that these metals share transport pathways in these distinct lineages. <i>K</i>_us and BCFs were substantially larger in Ephemerellidae than in Hydropsychidae, whereas <i>k</i>_es did not dramatically differ between the two families. Body size played an important role in driving <i>k</i>_u differences among species, but had no influence on <i>k</i>_es. 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

Evolutionary Patterns in Trace Metal (Cd and Zn) Efflux Capacity in Aquatic Organisms

The ability to eliminate (efflux) metals is a physiological trait that acts as a major driver of bioaccumulation differences among species. This species specific trait plays a large role in determining the metal loads that species will need to detoxify to persist in chronically contaminated environments and, therefore, contributes significantly to differences in environmental sensitivity among species. To develop a better understanding of how efflux varies within and among taxonomic groupings, we compared Cd and Zn efflux rate constants (k(e) values) among members of two species-rich aquatic insect families, Ephemerellidae and Hydropsychidae, and discovered that k(e) values strongly covaried across species. This relationship allowed us to successfully predict Zn efflux from Cd data gathered from aquatic species belonging to other insect orders and families. We then performed a broader, comparative analysis of Cd and Zn k(e) values from existing data for arthropods, mollusks, annelids, and chordates (77 species total) and found significant phylogenetic patterns. Taxonomic groups exhibited marked variability in k(e) magnitudes and ranges, suggesting that some groups are more constrained than others in their abilities to eliminate metals. Understanding broader patterns of variability can lead to more rational extrapolations across species and improved protectiveness in water quality criteria and ecological assessment

Evolutionary Patterns in Trace Metal (Cd and Zn) Efflux Capacity in Aquatic Organisms

The ability to eliminate (efflux) metals is a physiological trait that acts as a major driver of bioaccumulation differences among species. This species-specific trait plays a large role in determining the metal loads that species will need to detoxify to persist in chronically contaminated environments and, therefore, contributes significantly to differences in environmental sensitivity among species. To develop a better understanding of how efflux varies within and among taxonomic groupings, we compared Cd and Zn efflux rate constants (<i>k</i>_e values) among members of two species-rich aquatic insect families, Ephemerellidae and Hydropsychidae, and discovered that <i>k</i>_e values strongly covaried across species. This relationship allowed us to successfully predict Zn efflux from Cd data gathered from aquatic species belonging to other insect orders and families. We then performed a broader, comparative analysis of Cd and Zn <i>k</i>_e values from existing data for arthropods, mollusks, annelids, and chordates (77 species total) and found significant phylogenetic patterns. Taxonomic groups exhibited marked variability in <i>k</i>_e magnitudes and ranges, suggesting that some groups are more constrained than others in their abilities to eliminate metals. Understanding broader patterns of variability can lead to more rational extrapolations across species and improved protectiveness in water-quality criteria and ecological assessment