The Genetic Structure Features of the Amphimictic Earthworm Aporrectodea caliginosa (Oligochaeta, Lumbricidae) Populations within Ukraine

Genetic differentiation of the amphimictic earthworm A. caliginosa populations was investigated in the territory of Ukraine by analyzing the variability of the polyallelic locus Es-4. It was established that the settlements of this species are characterized by Fst = 0.13, which means genetic heterogeneity above the average level. The values of this index depend on the size of the population groups. Moreover, these changes can be represented as a leap from insignificant interdeme differences to statistically significant ones, obtained in the analysis of geographically remote populations, with the stabilization of the Fst index values on the macroscale. This situation is reasonable for the model of a genetically homogeneous settlement that arose once over a large area, the secondary differentiation of which was caused by internal migrations and the founder effect, which is in agreement with the regularities observed for populations of this species in North America.

The comparison of the spatial differentiation of A. caliginosa populations with the genetically, ecologically, and arealogically close parthenogenetic A. trapezoides species within Ukraine showed that the apomictic species has a different type of geographical differentiation of populations. It is characterized by a vicarious structure of settlements in which one clonal form replaces another and the genotypes of clones of distant populations differ the most. This means that there are no migrations between remote settlements of earthworms within Ukraine, and the reasons for the alternative nature of the genetic subdivision of amphimictic and apomictic species settlements are associated with the mechanisms of forming genetic diversity. In amphimictic species populations, the maximum genotypic diversity is achieved through recombinations and is realized at the individual level within populations, while it is due to mutations in clonal species and appears as intergroup variability.