Sibling species in the oligochaete worm Lumbricillus rivalis (Enchytraeidae) revealed by enzyme polymorphisms and breeding experiments

At least two sibling species were discovered in the oligochaete worm Lumbricillus rivalis Lev. by electrophoretic studies on the phosphoglucose isomerase (Pgi) and phosphoglucomutase (Pgm) loci and by breeding experiments. Based on the genetic differentiation, 22 populations studied were divided into three groups. This subdivision was correlated with differences in habitats. One of the groups is reproductively isolated from the other two, whereas the relationship between the latter remains unknown. The speciation is in some way associated with shift in the electrophoretic mobility of Pgi resulting in two assemblages, each containing a number of equidistant alleles. It is proposed that the speciation is associated with ecological adaptation to less saline environments.