Genotypic similarities among the parthenogenetic Darevskia rock lizards with different hybrid origins
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(2020) 20:122
RESEARCH ARTICLE
Open Access
Genotypic similarities among the parthenogenetic Darevskia rock lizards with different hybrid origins David Tarkhnishvili1* , Alexey Yanchukov2, Mehmet Kürşat Şahin3, Mariam Gabelaia1, Marine Murtskhvaladze1, Kamil Candan4, Eduard Galoyan5, Marine Arakelyan6, Giorgi Iankoshvili1, Yusuf Kumlutaş4, Çetin Ilgaz4, Ferhat Matur4, Faruk Çolak2, Meriç Erdolu7, Sofiko Kurdadze1, Natia Barateli1 and Cort L. Anderson1
Abstract Background: The majority of parthenogenetic vertebrates derive from hybridization between sexually reproducing species, but the exact number of hybridization events ancestral to currently extant clonal lineages is difficult to determine. Usually, we do not know whether the parental species are able to contribute their genes to the parthenogenetic vertebrate lineages after the initial hybridization. In this paper, we address the hypothesis, whether some genotypes of seven phenotypically distinct parthenogenetic rock lizards (genus Darevskia) could have resulted from back-crosses of parthenogens with their presumed parental species. We also tried to identify, as precise as possible, the ancestral populations of all seven parthenogens. Results: We analysed partial mtDNA sequences and microsatellite genotypes of all seven parthenogens and their presumed ansectral species, sampled across the entire geographic range of parthenogenesis in this group. Our results confirm the previous designation of the parental species, but further specify the maternal populations that are likely ancestral to different parthenogenetic lineages. Contrary to the expectation of independent hybrid origins of the unisexual taxa, we found that genotypes at multiple loci were shared frequently between different parthenogenetic species. The highest proportions of shared genotypes were detected between (i) D. sapphirina and D. 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 their origin to a single initial hybridization event. In case (ii), however, occasional gene exchange between the unisexual and 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 flow has been previously documented. Our results further suggest that parthenogens are losing heterozygosity as a result 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, and therefore increase the persistance of unisexual forms. Keywords: Darevskia, Parthenogenesis, Microsatellites, Mitochondrial DNA, Backcrosses, Allele conversion, Caucasian rock lizards
* Correspondence: [email protected]
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