Environmental niche divergence between genetically distant lineages of an endangered water beetle

Historically, there has been considerable disagreement between researchers about the criteria used to discriminate among species. Decisions based on traditional morphological and genetic data alone can be potentially problematic, especially if the hypotheses are contradictory. Today, taxonomy is integrating new methods from different disciplines that study species' limits and evolution; this diverse range of evidence aids researchers in the recognition of species. Differences in niche characteristics could become a new and useful criterion in helping to decide the status of conflicting taxonomical entities. Ochthebius glaber (family Hydraenidae) is an endangered water beetle typical from southeast Iberian hypersaline streams that shows three clear discrete genetic units within its distribution range. However, there is no evidence to date that these lineages of O. glaber exhibit any adaptive morphological or ecological divergence. Using a modelling approach directed to generate niche representation from distributional data, we found a significant environmental niche divergence for allopatric lineages of O. glaber that followed an aridity gradient. Although we can not conclude firmly at present that the separate populations of O. glaber studied represent separate, reproductively isolated species, the present study complements and supports previous phylogeographic analyses through the inclusion of measures of another form of evolutionary change; in this case, ecological diversification. Despite the existence of some methodological limitations, also discussed in the present study, we emphasize the importance of recent conceptual advances that allow taxonomy to improve species delimitation practices through the integration of theory and methods from disciplines that study the origin and evolution of species. (C) 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 891-903.