Mixed phylogenetic signal in fish toxicity data across chemical classes

Abstract

Chemical use in society is growing rapidly and is one of the five major pressures on biodiversity worldwide. Since empirical toxicity studies of pollutants generally focus on a handful of model organisms, reliable approaches are needed to assess sensitivity to chemicals across the wide variety of species in the environment. Phylogenetic comparative methods (PCM) offer a promising approach for toxicity extrapolation incorporating known evolutionary relationships among species. If phylogenetic signal in toxicity data is high, i.e., closely related species are more similarly sensitive as compared to distantly related species, PCM could ultimately help predict species sensitivity when toxicity data are lacking. Here, we present the largest ever test of phylogenetic signal in toxicity data by combining phylogenetic data from fish with acute mortality data for 42 chemicals spanning 10 different chemical classes. Phylogenetic signal is high for some chemicals, particularly organophosphate pesticides, but not necessarily for many chemicals in other classes (e.g., metals, organochlorines). These results demonstrate that PCM may be useful for toxicity extrapolation in untested species for those chemicals with clear phylogenetic signal. This study provides a framework for using PCM to understand the patterns and causes of variation in species sensitivity to pollutants.

Keywords: ecological risk assessment; ecotoxicology; evolutionary toxicology; fish; organochlorine; organophosphate; phylogenetic comparative methods; phylogeny.

Figure 1

Fish sensitivity to (a) organophosphate insecticides and (b) organochlorine compounds organized by taxonomic family. Only families with 10 or more species in the dataset are represented.

Figure 2

Phylogeny of fish with toxicity data overlaid from five organophosphates (malathion (Mal), azinphos-methyl (AZM), diazinon (Diaz), methyl parathion (MP), and trichlorfon (Tri)) with strong phylogenetic signal (i.e., λ > 0.5 and significantly different from 0). Toxicity data percentiles represent scaling of the LC₅₀ for each species-chemical pair as a proportion between the lowest and highest log-LC₅₀ value across all species for a given chemical. Fish family names are included in the tree next to corresponding taxon branches.