Quantum speciation in Aegilops:: Molecular cytogenetic evidence from rDNA cluster variability in natural populations

Data are presented on quantum speciation in the Sitopsis section of the genus Aegilops (Poaceae, Monocotyledones). Two small, peripheral, isolated, wild populations of annual cross-pollinated Ae. speltoides and annual self-pollinated Ae. sharonensis are located 30 m apart on different soil types. Despite the close proximity of the two species and their close relatedness, no mixed groups are known. Comparative molecular cytogenetic analysis based on the intrapopulation variability of rRNA-encoding DNA (rDNA) chromosomal patterns of individual Ae. speltoides genotypes revealed an ongoing dynamic process of permanent chromosomal rearrangements. Chromosomal mutations can arise de novo and can be eliminated. Analysis of the progeny of the investigated genotypes testifies that inheritance of de novo rDNA sites happens frequently. Heterologous recombination and/or transposable elements-mediated rDNA transfer seem to be the mechanisms for observed chromosomal repatterning. Consequently, several modified genomic forms, intermediate between Ae. speltoides and Ae. sharonensis, permanently arise in the studied wild population of Ae. speltoides, which make it possible to recognize Ae. sharonensis as a derivative species of Ae. speltoides, as well as to propose rapidness and canalization of quantum speciation in Sitopsis species.