DNA studies in European Clausiliidae
Hartmut Nordsieck (X.2018)
The molecular studies of European Clausiliidae published until now were carried out by the following working groups (studied taxa groups in brackets):
Leiden group (AICC group, Balea);
Hamburg group (Charpentieria, Clausilia, Micropontica, Alopia);
Vienna (-Budapest) group (Alopia, Agathylla, Montenegrina);
Greek (Athens + Patras + Iraklion) groups (Albinaria);
Urbino (-Sicily) group (Muticaria, Medora).
Initially, multiple enzymes = allozymes in closely related taxa were used by the Leiden working group until 2001 (GITTENBERGER et al. 2001), then DNA data since1995 (SCHILTHUIZEN et al., DOURIS et al.). The allozyme studies are not discussed in this article.
For DNA studies two methods were applied:
1. Sequence studies (single-locus data):
mtDNA: COI, COII, 12S, 16S, ATPase 8;
nDNA: rRNA gene (with internal transcribed spacers = ITS): - 18S - ITS1 - 5.8S - ITS2 - 28S - or only ITS1 or ITS2, intron of Calmodulin = CaM, Histone genes = H3, H4.
2. Amplified fragment length polymorphism = AFLP studies (multi-locus data):
AFLP is a method to obtain DNA finger-prints (= multi-locus data) with the help of restriction enzymes.
For the authors and dates of the taxa names used in this article see taxa list of Clausiliidae (NORDSIECK 2007: chapter II)..
II. DNA studies of European Clausiliidae
SAUER (2011: 118, 143, 148) in his thesis (though not on Clausiliidae) has given some important statements for taxonomic DNA studies which are cited here as basic for the comments in this article:
1. Taxonomy in general: „ ... plead for an integrative taxonomy ... combining morphological and molecular approaches to unravel biodiversity.“
2. Morphological data: „ ... that most complex morphological characters are influenced by several loci ..., and thus can be understood as a sort of coding of multi-locus data. “
3. Gene trees: „Given the differences between gene trees based on different markers, it is not surprising that there are large disagreements between molecular ... taxonomic units ..., based on different markers. “
4. Taxa trees: „ ... any serious attempt to establish the taxonomy of a group should be based on an analysis of several independent markers. “
5. Single-locus data: „ ... species classifications based exclusively on single-locus data might show idiosyncrasies resulting from incomplete lineage sorting, introgression, random phylogeographic breaks or pseudogenes. “ , therefore „... taxonomy should not rely exclusively on single-locus markers.“
6. Multi-locus data: „... resulting partitions ... based on single-locus data are less similar to those ... of the AFLP data or to the morphological classification than the partitions obtained by ... the AFLP data ... to the morphological classification. “
The last statement has been confirmed by following papers of the Hamburg group (SCHEEL & HAUSDORF 2012, HAUSDORF & NÄGELE 2015).
AFLP data are especially useful for phylogenetic studies of nearly related taxa and the analysis of hybridization (allowing admixture analyses of gene flow among populations). Difficult to understand, why this method was used until now only by that working group, though interspecies hybridization plays an important role also in the other studied clausiliid groups from southern Europe (see article on interspecies hybridization, NORDSIECK unpubl.).