The hermaphroditic, facultatively selfing, land snail Rumina decollata is a common, widespread species indigenous in the western Mediterranean region, that has been introduced in many other parts of the world. Recent DNA sequence analyses have shown that R. decollata is a complex of several (phylogenetic) species, two of them corresponding to previously distinguished allozyme strains with different body colours (light vs. dark). Therefore, considering this new taxonomic interpretation, we here attempt to identify which, and how many, species of the R. decollata complex have been introduced outside their native area. Comparative DNA sequence analysis of introduced populations from South America, North America, Japan and the North Atlantic Islands vs. native populations from the Mediterranean area, revealed that all introduced populations belong to one single phylogenetic species, previously recognized as the dark strain. Therefore, the colonizing and invasive character of R. decollata is mainly, if not entirely, due to this dark strain. Furthermore, the Iberian Peninsula seems to be an important source for introduced R. decollata populations outside Europe. Within this work, we will discuss about the invasive character of the dark strain and the possible source areas of the introduced populations.

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