Resolving reticulate speciation in bisexual and parthenogenetic lizards of genus Darevskia in east Anatolia and Caucasus

Erdolu, Meriç
The genus Darevskia (rock lizards) from East Anatolia, Georgia and Armenia represents a rare biological system where both sexually reproducing and parthenogenetic forms are found together. In total, seven nominal parthenogenetic species (D. unisexualis, D. rostombekovi, D. dahli, D. sapphirina, D. bendimahiensis, D. uzzelli) are estimated to have formed several hundred thousand years ago via interspecific hybridization between four bisexual species, of which two (D. mixta and D. raddei) always acted as maternal and two (D. valentini and D. portschinskii) acted as paternal parents. The same parental pairs were able to produce different parthenogenetic species, each of which possesses distinct morphologies and ecological preferences. The Darevskia system can thus offer a unique insight into genetic mechanisms of the origin and maintenance of parthenogenesis in vertebrates since the process of hybridization has occurred in parallel. The dissertation is composed of four chapters. In Chapter 1, we introduce the genus Darevskia and summarize the studies on this genus. Also, we give the objectives of the thesis. In Chapter 2, we describe in detail the methods used in the study. In Chapter 3, I present my contribution to a published study on the paternal origin and phylogenetic history of all seven parthenogenetic species. In this study, we analyzed genomic data of specimens from the bisexual species Darevskia raddei (n=25), D. portschinskii (n=9), D. mixta (n=12), D. valentini (n=18), D. derjugini (n=1), and D. rudis (n=6), as well as the parthenogenetic species D. sapphirina (n=8), D. bendimahiensis (n=10), D. rostombekovi (n=6), D. dahli (n=11), D. uzzelli (n=8), D. unisexualis (n=7), and D. armeniaca (n=13) species. With this data we aimed to identify those extant bisexual populations that are genetically closest to the actual paternal progenitors of the parthenogenetic species. We used 12,650 Z-chromosomal ddRAD-seq loci and several bioinformatics methods and tools for population genetics analysis. We found that the most likely paternal ancestor of each parthenogenetic species is also the geographically nearest one. Also, we found that hybridization seemed to have occurred during two time periods (0.83 Mya and 1.57 Mya). In Chapter 4, we reveal the genetic details of the origin of two nominal parthenogenetic species D. sapphirina and D. bendimahiensis, endemic to Lake Van basin. The analysis was based on 1,381,322 autosomal ddRAD-seq loci. In line with the previous results based on 10 microsatellite markers as well as Z-linked ddRAD loci, the two nominal species were found to be indistinguishable genetically and should be revised into a single taxon. Their most likely paternal ancestor is the population of D. valentini from Çaldıran, located only 4 km away from the nearest population of D. bendimahiensis. In contrast, the most likely maternal ancestor of D. sapphirina and D. bendimahiensis is the geographically distant population of D. raddei from Doğubayazıt population in the Aras river basin, not the sympatric D. raddei population in the Lake Van basin. Finally, we designed and employed several methods to estimate the number of hybridization events that led to the origin of D. bendimahiensis / D. sapphirina. The pattern of allele frequency correlation between the parental and parthenogenetic population, as well as the presence of multiple ddRAD loci with three distinct alleles, do not support the null hypothesis of a single hybridization event between just two individuals of the parental species. The paper draft summarising these fundings is currently in preparation.


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Citation Formats
M. Erdolu, “Resolving reticulate speciation in bisexual and parthenogenetic lizards of genus Darevskia in east Anatolia and Caucasus,” Ph.D. - Doctoral Program, Middle East Technical University, 2023.