Cytogenetic and genetic trends in the evolution of unisexual lizards.

Extensive karyological, allozyme and molecular genetic analyses of many parthenogenetic lizards confirm the origin of these species by hybridization. The concept of reticulate (hybridogeneous) speciation based on 3 interrelated phenomena such as hybridization-unisexuality-polyploidy has been elaborated. Cytogenetic and genetic variability and some regular trends in the evolution of hybrid unisexual species have been demonstrated. Cytogenetic investigations of unisexual-bisexual complex lizards of the genus Darevskia (formerly Lacerta) in the family Lacertidae suggest that some characteristics of their karyotypes play a role in the evolution of parthenogenesis. The maternal species with advanced w sex microchromosomes (Zw type) appeared to be successful in hybridization and produced the diploid unisexual species. The polyploid back-cross hybrids between said diploids and bisexual parent species exhibited many chromosome aberrations which were associated with their complete or partial sterility. In addition, the karyotype and the structure of mitotic and meiotic lampbrush chromosomes in 2 species and in some back-cross hybrids of this unisexual-bisexual complex have been examined here using molecular cytogenetic techniques. The genomic and functional disturbances, genomic interactions between homeologous chromosomes, and possibly both genomic imprinting and the presence of mobile elements are some cytogenetic mechanisms that increase genetic diversity in hybrid parthenogenetic species.