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Darevskia unisexualism

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The all-female Caucasian rock lizard Darevskia rostombekowi and other unisexual species of this genus reproduce normally via true parthenogenesis.

Typically, diploid parthenogenetic reptiles exhibit some amount of clonal diversity. However, allozyme data from D.

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Herein, we test this hypothesis by evaluating variation at three variable microsatellite loci for 42 specimens of D. Analyses based on single nucleotide polymorphisms of each locus reveal five genotypes Darevskia unisexualism presumptive clones in this species.

All individuals are heterozygous at the loci. The major clone occurs in 24 individuals and involves three populations. Four rare clones involve one or several individuals from one or two populations. Most variation owes to parent-specific single nucleotide polymorphisms, which occur as heterozygotes.

This result fails to reject the hypothesis of a single hybridization founder event that resulted in the initial formation of one major clone. The other clones Darevskia unisexualism to have originated via post-formation microsatellite mutations of the major clone. Questions concerning origin and evolution of parthenogenesis in lizards have received considerable attention in recent years [ 1 — Darevskia unisexualism ].

Parthenogenetic lizard species are ideal organisms for studying the genetic and ecological basis of hybridogeneous speciation, understanding the mechanisms of hybrid parthenogenesis, generation and Darevskia unisexualism of genetic diversity, determination of possible factors of natural selection, and hybrid disfunction caused by genetic incompatibilities of admixed genomes or re-established balance of cytonuclear genomes.

Unisexual species have been found in less than 0. Among vertebrates, true parthenogenesis, where reproduction proceeds without male participation, has been detected in squamate reptiles, especially in lizards [ 7 ] and also in the brahminy blind snake Indotyphlops braminus [ 89 ]. It also occurs in Darevskia unisexualism vertebrate groups, e. The Lacertidae was the first family in which this phenomenon was discovered [ 11 ].

In most known instances, parthenogenetic species originated from interspecific hybridization between closely related bisexual species [ 1213 ], but these may not be sister-species [ 14 ].

Only parthenogenetic species of Lepidophyma L.

Further studies are necessary in these exceptional cases. The hypothesis of hybrid origin postulates that two species interbred and produced viable offspring that then reproduced clonally. According to the balance hypothesis [ 16 ], a new successful, clonal species can be established if genetic differences between the hybridizing species Darevskia unisexualism sufficient to disrupt recombination during meiosis and while not severely limiting viability, fecundity, and other characteristics affecting fitness of the hybrid species.

In other words, hybridization is dependent on phylogenetic distance. In contrast, the phylogenetic constraint hypothesis of Darevsky states that hybridization is "Darevskia unisexualism" linage dependent [ 17 ].

Because of their hybrid origin, parthenogenetic Darevskia unisexualism combine much of the genetic diversity of two parental sexual species. They are normally diploid as in Darevskia or triploid as in Aspidoscelis and commonly exhibit high levels of nuclear gene diversity because of fixed heterozygosity at codominant loci [ 18 ]. The more divergent hybridizing parental species are, the greater ability to persist in nature over many generation because distinct parental alleles form heterozygous loci in the hybrid genome.

Darevskia unisexualism pairing provides a mechanism for maintaining heterozygosity, which is critical for offsetting the reduced fitness in parthenogenetic species [ 19 ]. Each parthenogenetic species usually consists of several clonal lineages, Darevskia unisexualism caused by either mutations especially in hypervariable microsatellite locimultiple origins from different pairs of founders, rare new hybridization events, or some level of genetic recombination [ 162021 ].

Clonal diversity also appears to correlate with the size of the area of origin, distinct ecological conditions of the habitat, and age of parthenogenetic species [ 22 — 24 ]. Based on patterns of allozyme variation observed among parthenogenetic species of a number lizard genera, Parker et al.

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