Restriction fragment patterns as molecular markers for species identification and phylogenetic analysis in the genus Enchytraeus (Oligochaeta)1

Species identification in the Enchytraeidae is extremely difficult as in many groups of lower invertebrates. Clear-cut morphological character differences which would allow an unambiguous delimitation are almost totally lacking between numerous species. Consequently, their identification and their phylogenetic relationships cannot be discerned by classical morphological methods alone. We show in this study that comparative analysis of DNA fragment variation found by restriction endonuclease digestions provide a suitable means for both species identification and analysis of their phylogenetic relationships. We have studied fragment length variation of ubiquitin and 18S rRNA genes in ten different populations of the genus Enchytraeus. Two populations which belong to the two species E. albidus and E. fragmentosus can be clearly identified by their restriction fragment patterns. The remaining eight populations are grouped into four clusters. The fragment patterns are identical within each group but differ considerably between these groups. Since the differences between these groups and between the two well characterized species are in the same range, it is suggested that these four groups may represent four different Enchytraeus-species. Phylogenetic analysis using Wagner maximum parsimony reveals a clearly defined pattern of relationships of the species studied.