The investigation of genetic structure of Aporrectodea caliginosa – A. trapezoides diploid – polyploid complex on the territory of Ukraine has been done both with biochemical gene marking of 6 loci(Aat, Es-1,-2,-3, -4, Mdh) and karyotyping. All 646 individuals of 21 samples were analyzed on the biochemical gene level. Karyotype preparations were received from 70 specimens. As a result diploid amphimictic А caliginosa individuals (2n=36) forming panmictic populations and triploid (2n=54) A.trapezoides ones represented by 20 supposed clones were clearly differentiated in 157 specimens. A clear tendency of triploid form domination in the steppe zone of Ukraine where they form 70% in comparison to 12% of all A. (superspecies) in the northern forest regions was detected. Taking into account the constant heterozygosity of the investigated loci and chromosome reaction in meiosis, the clone forms are allotriploids formed as a result of close species hybridization, but according to allele pools the amphimictic species living in Ukraine is absent. It means that either apomictic clones of A. trapezoides are not of the local origin and their appearance in the fauna of Ukraine is the result of earthworm introduction into the arid steppe regions or amphimictic A. caliginosa is an invasive species.
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