Molecular evidence for repetitive parallel evolution of shell structure inClausiliidae (Gastropoda, Pulmonata)

The division of clausiliid genera, using the type of clausilial apparatus ( CA) as the decisive criterion, is ambiguous. Two types of CA can be disting uished: the normal (N) type and the Graciliaria (G) type. Morphological res emblance between species with different types of CA led to the hypothesis t hat the CA type is homoplasious. Therefore sequence variation, phylogenetic relationships, and the evolution of the CA were studied in the genera Albi naria, Isabellaria, and Sericata. Phylogenetic relations were inferred from parsimony and neighbor-joining analyses of the nucleotide sequences of bot h internal transcribed spacers (ITS1 and ITS2) of the rDNA of 36 species. T he variation among the sequences was great: 21.8% of the sequences were amb iguously aligned and excluded from the analysis. A high GC content in the u nambiguously aligned portions and a substitutional bias toward a higher GC content are indicators of substitutional constraints in the spacers. We ana lyzed the data in several ways: using both spacers together and separately, weighting all mutations equally, correcting for transition/transversion bi as by weighting, and using transversions only. In all resulting trees, Isab ellaria is not a monophyletic group. Its division into two clades is suppor ted by over 40 mutations and one large indel. Clade 1 consists of Isabellar ia and Sericata and clade 2 consists of Isabellaria and Albinaria species. The present distribution of the CA type was plotted on the tree and its mos t parsimonious evolution was reconstructed. The CA type was shown to be hig hly homoplasious. In clade 1 and clade 2 both types of CA were found; depen ding on the ancestral state, either the G or the N type evolved several tim es in parallel. These results contribute decisively to the current debate o n the morphological diagnoses of Albinaria, Sericata, and Isabellaria as mo nophyletic taxa. (C) 2000 Academic Press.