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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 as 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.

Угруповання дощових червів відкритих ландшафтів України виявляють географічну неоднорідність, пов’язану з видоспецифічними особливостями розмноження видів, що до них належать. Якщо в північно-західних областях України переважають амфіміктичні види, то в східних і південних домінують партеногенетичні. Альтернативний характер поширення партеногенетичних й амфіміктичних видів у напрямку з північного заходу на південний схід підтверджено кореляційним аналізом. Також виявлено негативну залежність між видовим різноманіттям угруповання на регіональному рівні та представленістю в ньому партеногенетичних дощових червів. Переважання партеногенетичних видів в областях із сухим і континентальним кліматом та збідненим видовим складом дає підставу вважати адекватним застосування концепції географічного партеногенезу щодо закономірностей поширення амфіміктичних і партеногенетичних видів дощових червів. При цьому немає підстав вважати партеногенетичних люмбрицид екстремофілами, в даній ситуації більш точним буде їх віднесення до високотолерантних організмів. The earthworms communities of the open landscapes of Ukraine confirm the geographic heterogeneity associated with the species-specific peculiarities of the reproduction of the constituent species. In the northwestern regions of Ukraine predominating species are amphimictic, otherwise in the eastern and southern regions the parthenogenetic species are dominating. The alternative character of the distribution of parthenogenetic and amphimictic species in the direction from northwest to southeast is confirmed by correlation analysis. It was revealed a negative dependence between the species richness of the community at the regional level and the representation of parthenogenetic earthworms in it. The predominance of parthenogenetic species in areas with dry and continental climates and depleted species composition gives the reason to consider the application of the concept of geographic parthenogenesis to the distribution of patterns of amphimictic and parthenogenetic earthworms species. Besides, there is no reason to consider parthenogenetic lumbricids are extremophiles; in this situation, it would be more accurate to classify them as highly tolerant organisms.

Geographical parthenogenesis describes phenomenon when parthenogenetic hybrid forms or species have larger distribution areas or higher abundance than their amphimictic parental species, especially in climatically unfavorable conditions. This phenomenon was studied in Ukraine for the pair species of earthworms Aporrectodea сaliginosa (Savigny, 1826) s. l. We found that the hermaphroditic amphimictic A. caliginosa clearly predominates in the northern and western regions, and the apomictic parthenogenetic A. trapezoides (Duges, 1828) in the southern and eastern regions with a continental arid climate. In the sample sets of A. сaliginosa–A. trapezoides group, usually one of the species sharply predominated, and the equality of their abundance was very rare. The reason for this fact is both the alternative geographical distribution and the ability of A. trapezoides to form populations in habitats unfavorable for A. caliginosa. In general, the situation in this group agrees with the classical model of geographic parthenogenesis and confirms the high adaptive potential of apomictic organisms. This fact once again raises the question of non-adaptive reasons for the exclusion of the apomictic reproduction in highly organized animals.