Taxonomic Significance of Ribosomal ITS-1 Sequence Markers in Self-fertilizing Land Snails of Cochlicopa (Stylommatophora, Cochlicopidae)

Abstract

The Internal Transcribed Spacer 1 (ITS-1) of the ribosomal RNA genes is analysed in a group of highly self-fertilizing land snails. Sequences are provided for the nominal species Cochlicopa lubricella (Porro 1838), C. nitens (Gallenstein 1848) and C. lubrica (O. F. Müller 1774). The three nominal species exhibit a very low interspecific sequence variation. The length of the ITS-1 varies between 555 and 585 basepairs. A total of thirty-one variable nucleotide positions could be found within ten clones. Out of these variable positions seven markers are useful for taxonomic considerations. Two nucleotide markers support the delimitation of C. nitens, three markers are available for the delimitation of the group termed C. lubricella type 2, one nucleotide marker supports the grouping of C. lubrica & C. lubricella type 1, and one marker is available for the characterization of C. lubricella type 1. These seven markers clearly confirm the taxonomy based on RAPD fingerprinting and allozyme patterns (Armbruster, G. [1997]: Journal of Molluscan Studies 63: 379-388). The overall evaluation of the molecular data shows that the snails traditionally classified as Cochlicopa lubricella (Porro 1838) encomprise a paraphyletic arrangement of highly self-fertilizing gastropods. The members of this paraphyletic group share morphological similarities, i.e. small and slender shells. Hence, subjectively similar morphotypes of snails need not always belong to a monophyletic taxon. Furthermore, the ITS-1 of another cochlicopid snail, Azeca goodalli (Férrusac 1821), is analysed. This species shows an ITS-1 length of 609 bp, which presently is the longest ITS-1 sequence reported for pulmonate gastropods. Overall, Azeca goodalli shows a high genetic distance to Cochlicopa.