Coincidence of genotypes at two loci in two parthenogenetic rock lizards: how backcrosses might trigger adaptive speciation

Abstract

The parthenogenetic lizards Darevskia armeniaca and Darevskia dahli are widespread throughout the Lesser Caucasus, although they occupy different habitats. While these forms differ in size, colour and scalation, both D. armeniaca and D. dahli have a hybrid origin and a common maternal progenitor species. Current evidence about the patrilineal origin is inconclusive, and the exact number of ancestral lineages remains unknown. This study aimed to investigate the distribution of mitochondrial haplotypes and alleles at five microsatellite loci in both the parthenogenetic forms and their presumed ancestors, in order to infer the number of ancestral hybridization events. Mitochondrial DNA analysis confirmed that both forms descend matrilineally from D. mixta from a limited geographic area in Central Georgia. Simultaneously, the majority of both D. armeniaca and D. dahli shared the same genotypes at two microsatellite loci, but differed at the other three. This observation and overall study of the distribution of the microsatellite genotypes suggests that (1) both D. armeniaca and D. dahli descend from very few, possibly single original hybridization event, most likely D. mixta and D. portschinskii, hence the hypothesis of different paternal species for these two forms is rejected; (2) expansion of the original parthenogenetic hybrid form into the range of D. valentini, followed by backcrosses of D. valentini males with the parthenogens, triggered development of a new parthenogenetic form, D. armeniaca; (3) backcrosses and mutation are more likely reasons of genetic diversity both between and within the parthenogenetic forms than their multiclonal origin.