A comparison of DNA-based methods for delimiting species in a Cretan land snail radiation reveals shortcomings of exclusively molecular taxonomy.

We compared the results of different approaches for delimiting species based on single-locus DNA sequences with those of methods using binary multilocus data. As case study, we examined the radiation of the land snail genus Xerocrassa on Crete. Many of the methods based on mitochondrial sequences resulted in heavy under- or overestimations of the species number. The methods using AFLP data produced classifications with an on average higher concordance with the morphological classification than the methods based on mitochondrial sequences. However, the percentage of correct species classifications is low even with binary multilocus data. Gaussian clustering produced the classifications with the highest concordance with the morphological classification of all approaches applied in this study, both with single-locus sequences and with binary multilocus data. There are two general problems that hamper species delimitation, namely rarity and the hierarchical structure of biodiversity. Methods for species delimitation using genetic data search for clusters of individuals, but do not implement criteria that are sufficient to distinguish clusters representing species from other clusters. The success of morphological species delimitation results from the potential to focus on characters that are directly involved in the speciation process, whereas molecular studies usually rely on markers that are not directly involved in speciation. © The Willi Hennig Society 2011.