Loss of allelic diversity in species of hybrid origin

Abstract

Species of hybrid origin support their population as a rule by cloning. Switching over of any bisexual organism to propagation by means of parthenogenesis, gynogenesis, androgenesis (or other kind of apomictic reproduction without regular recombination, which usually accompanies change of generations in bisexual species) leads to rapid decrease of genetic polymorphism. Long-term cloning transforms the polymorphic population or entire species into a mixture of only a few clones, composed of genetically identical individuals. owing to selection in favour of heterozygotes or due to hybrid origin, natural clonal populations commonly are of high heterozygosity. Selection, genotypic uniformity and high heterozygosity often give to clonal race or species selective advantages, but at the same time they inevitably result in loss of most of alleles. Inasmuch as new forms, reproductively isolated from parental species, are products of hybridization of only a small number of individuals, which succeed in overcome the interspecies barrier, the hybridization itself also plays role of a very narrow bottle neck. The well established opinion that recombination and allelic diversity are necessary conditions for successful evolution on the basis of gene frequency changes, comes now into contradiction with the available data concerning the polyploid and, probably, hybrid origin of many groups of flowering plants and vertebrate animals.