Tendency towards clonality: deviations of meiosis in parthenogenetic Caucasian rock lizards

Abstract

Abstract Cytogenetic mechanisms of unisexuality in diploid parthenogenetic species of genus Darevskia remained debatable until recently. The mechanism that allows the unisexual form to maintain its heterozygosity in a number of generations is important for long-term existence in nature. In this work, for the first time for a parthenogenetic species of genus Darevskia, in addition to primary oocytes with the usual ploidy (18 + ZW bivalents in the meiotic prophase I) oocytes that underwent premeiotic genome endoduplication and carry a doubled number of bivalents (36 + ZZ + WW) were found. Here we present a detailed comparative analysis of total preparation of synaptonemal complexes in the oocyte nuclei without and with genome endoduplication, and the behavior of sex Z and W chromosomes. We show the details of assembly of bivalents in the pachytene nuclei, where either homeologues or doubled identical copies of chromosomes compete for synapsis and form multivalents. For the first time, the WW sex pseudobivalent has been visualized in parthenogenetic reptiles. We show the reverse side of meiotic deviations in obligate parthenogenesis - cases of non-viable embryos with specific abnormalities.