Phylogeography of the land snail Abida secale (Draparnaud, 1801) (Chondrinidae).

Extreme morphological variation in the land snail Abida secale has been categorized in 17 currently recognized subspecies. Fourteen of these occur in a relatively small area of the species' range. Within this subspecies complex, based on shell morphological analyses, a ‘ring-species’ scenario has been postulated. To evaluate this scenario and to define (sub)species boundaries within the complex, the mitochondrial marker cytochrome oxidase I was analysed. The phylogeny reconstruction reveals two clades in Abida secale. These clades do not correspond to subspecies definitions based on shell morphological analyses. One clade of A. secale has A. attenuata, a morphologically well-defined species, as its sister taxon. These results could be explained by either incomplete lineage-sorting of the mitochondrial genome and/or by introgression of the A. attenuata mitochondrial genome into A. secale. Circumstantial evidence favours the second scenario. Whichever scenario has caused the observed pattern, the results of the mitochondrial DNA analyses do not show evidence of reduced gene flow between A. s. cadiensis and A. s. cadica. Since these two subspecies are the postulated ‘ends’ of the ring, there was no support for a ring-species scenario in Abida secale. [ABSTRACT FROM PUBLISHER]