Genotypic similarities among the parthenogenetic Darevskia rock lizards with different hybrid originsстатья
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Аннотация:Background: The majority of parthenogenetic vertebrates derive from hybridization between sexually reproducingspecies, but the exact number of hybridization events ancestral to currently extant clonal lineages is difficult todetermine. Usually, we do not know whether the parental species are able to contribute their genes to theparthenogenetic vertebrate lineages after the initial hybridization. In this paper, we address the hypothesis, whethersome genotypes of seven phenotypically distinct parthenogenetic rock lizards (genus Darevskia) could haveresulted from back-crosses of parthenogens with their presumed parental species. We also tried to identify, asprecise as possible, the ancestral populations of all seven parthenogens.Results: We analysed partial mtDNA sequences and microsatellite genotypes of all seven parthenogens and theirpresumed ansectral species, sampled across the entire geographic range of parthenogenesis in this group. Ourresults confirm the previous designation of the parental species, but further specify the maternal populations thatare likely ancestral to different parthenogenetic lineages. Contrary to the expectation of independent hybrid originsof the unisexual taxa, we found that genotypes at multiple loci were shared frequently between differentparthenogenetic species. The highest proportions of shared genotypes were detected between (i) D. sapphirina andD. bendimahiensis and (ii) D. dahli and D. armeniaca, and less often between other parthenogens. In case (ii),genotypes at the remaining loci were notably distinct.Conclusions: We suggest that both observations (i-ii) can be explained by two parthenogenetic forms tracing theirorigin to a single initial hybridization event. In case (ii), however, occasional gene exchange between the unisexualand the parental bisexual species could have taken place after the onset of parthenogenetic reproduction. Indeed,backcrossed polyploid hybrids are relatively frequent in Darevskia, although no direct evidence of recent gene flowhas been previously documented. Our results further suggest that parthenogens are losing heterozygosity as aresult of allelic conversion, hence their fitness is expected to decline over time as genetic diversity declines.Backcrosses with the parental species could be a rescue mechanism which might prevent this decline, andtherefore increase the persistance of unisexual forms.