Cryptic species in ecotoxicology.

Abstract

The advent of genetic methods has led to the discovery of an increasing number of species that previously could not be distinguished from each other on basis of morphological characteristics. Even though we observe an exponential growth of publications on cryptic species, cryptic species are rarely considered in ecotoxicology. Thus, particularly the question of ecological differentiation and sensitivity of closely related cryptic species is rarely addressed. Tackling this question, however, is of key importance for evolutionary ecology, conservation biology and, in particular, regulatory ecotoxicology. At the same time, the use of species with (known or unknown) cryptic diversity might be a reason for the lack of reproducibility of ecotoxicological experiments and implies a false extrapolation of the findings. Our critical review includes a database and literature search, where we investigated how many of the species most frequently used in ecotoxicological assessments show evidence for cryptic diversity. We found a high proportion of reports indicating overlooked species diversity, especially in invertebrates. In terrestrial and aquatic realms, at least 67% and 54% of commonly used species were identified as cryptic species complexes, respectively. The issue is less prominent in vertebrates, where we found evidence for cryptic species complexes in 27% of aquatic and 6.7% of terrestrial vertebrates. We further exemplified why different evolutionary histories may significantly determine cryptic species' ecology and sensitivity to pollutants. This in turn may have a major impact on the results of ecotoxicological tests and, consequently, the outcome of environmental risk assessments. Finally, we provide a brief guideline on how to practically deal with cryptic diversity in ecotoxicological studies in general and its implementation in risk assessment procedures in particular.