Irregularities in Meiotic Prophase I as Prerequisites for Reproductive Isolation in Experimental Hybrids Carrying Robertsonian Translocations

The basic causes of postzygotic isolation can be elucidated if gametogenesis is studied, which is a drastically different process in males and females. As a step toward clarifying this problem, we obtained an experimental inbred lineage of the eastern mole vole Ellobius tancrei, whose founder animals were animals with identical diploid numbers 2n = 50 but with different Robertsonian translocations (Rb), namely 2Rb4.12 and 2Rb9.13 in the female and 2Rb.2.18 and 2Rb5.9 in the male. Here, we analyzed strictly inbred hybrids (F1, fertile and F10, sterile) using immunocytochemical methods in order to study spermatocytes during the meiotic prophase I. Previously, the presence of trivalents was assumed to have no significant effect on spermatogenesis and fertility in hybrids, but we demonstrated that spermatogenesis might be disturbed due to the cumulative effects of the retarded synapses of Rb bivalents as well as trivalents and their associations with XX sex bivalents. Alterations in the number of gametes due to the described processes led to a decrease in reproductive capacity up to sterility and can be examined as a mechanism for reproductive isolation, thus starting speciation.