Сhayka Y. Geographical parthenogenesis and peculiarities of reproduction of diploid and triploid representatives of the earthworm Aporrectodea caliginosa - trapezoides (Oligochaeta, Lumbricidae)

The dissertation is devoted to the evolution of sexual reproduction and focuses on the causes and mechanisms of biological progress of obligate parthenogenetic organisms using earthworms as an example. The work is comparative research of the reproductive efficiency, geographical distribution and population structure of two species of earthworms - the diploid amphimictic Aporrectodea caliginosa and the closely related hybrid triploid parthenogenetic species A. trapezoides, which have the same size, sympatric habitats and form common settlements. The settlements of A. caliginosa within Ukraine are characterized by an Fst index of 0.13, which indicates above-average genetic heterogeneity. The reasons for the alternative nature of the genetic distribution of settlements of amphimictic A. caliginosa and apomictic species A. trapezoides are related to the mechanisms of genetic diversity formation. In populations of amphimictic species, the maximum genotypic diversity is achieved through recombination and is realized at the individual level within populations, while in clonal species it is caused by mutations and manifests itself mainly as intergroup variability. The level of individual fecundity in the parthenogenetic species A. trapezoides is slightly higher than in the amphimictic A. caliginosa. At the same time, despite a slight decrease in the number of juveniles, the total number of offspring surviving in culture in A. trapezoides is not lower than in A. caliginosa, which indicates that the fertility level of the parthenogenetic species also is not lower than that of the amphimictic species. The analysis of the literature proves that amphimictic and related apomictic species with obligate parthenogenesis don’е fundamentally differ in terms of individual fecundity and fertility. Therefore, mitotic gametogenesis, in terms of the quantity and quality of female sexual products, is no less effective a way of gamete formation than meiosis, which is characteristic of multicellular representatives of the animal kingdom.