Abstract
Knowing whether triploid hybrids resulting from natural hybridization of parthenogenetic and bisexual species are fertile is crucial for understanding the mechanisms of reticulate evolution in rock lizards. Here, using males of the bisexual diploid rock lizard species Darevskia raddei nairensis and Darevskia valentini and a triploid hybrid male Darevskia unisexualis × Darevskia valentini, we performed karyotyping and comparative immunocytochemistry of chromosome synapsis and investigated the distribution of RAD51 and MLH1 foci in spread spermatocyte nuclei in meiotic prophase I. Three chromosome sets were found to occur in cell nuclei in the D. unisexualis × D. valentini hybrid, two originating from a parthenogenetic D. unisexualis female and one from the D. valentini male. Despite this distorted chromosome synapsis and incomplete double-strand breaks repair in meiotic prophase I, the number of mismatch repair foci in the triploid hybrid was enough to pass through both meiotic divisions. The defects in synapsis and repair did not arrest meiosis or spermatogenesis. Numerous abnormal mature spermatids were observed in the testes of the studied hybrid.
Highlights
The discovery of parthenogenetic reproduction in the rock lizards of genus Darevskia Arribas, 1997 [1,2,3] raised a fundamental biological question about the evolutionary mechanisms within complex taxons
We found that the process of homologous and homeologous chromosome synapsis compete in spematocytes of the triploid male under study
We found that spermatocytes of the triploid hybrid pass through meiotic prophase I, as well as through both meiotic divisions
Summary
The discovery of parthenogenetic reproduction in the rock lizards of genus Darevskia Arribas, 1997 [1,2,3] raised a fundamental biological question about the evolutionary mechanisms within complex taxons. The hybrid origin of unisexual species in rock lizards was an important proof of the role of reticulate evolution [4] in vertebrates generally, and in Darevskia genus in particular [5,6,7,8,9]. The patterns of fusions of the close phylogenetic lineages resemble a network, rather than a tree [8]. Both diploidy and polyploidy occur in parthenogenetic reptile species, which have mechanisms to avoid the classical meiosis scenario. Cnemidophorus) [20,21,22]
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