Publishedonline 16 May 2003 Ecologicaland evolutionar yopportunitiesof apomixis: insightsfrom Taraxacum and Chondrilla Peter J.van Dijk NetherlandsInstitute ofEcology (NIOO-KNAW), Centre for Terrestrial Ecology, Boterhoeksestraat 48, 6666 GA Heteren, TheNetherlands (
[email protected] ) The ecological andevolutionary opportunitiesof apomixis in theshort and the long term are considered, basedon two closely related apomictic genera: Taraxacum (dandelion)and Chondrilla (skeletonweed). In both genera apomicts have awidergeographical distribution than sexuals,illustrating theshort-term eco- logical successof apomixis. Allozymes andDNA markers indicatethat apomictic populations are highly polyclonal. In Taraxacum,clonal diversity canbe generated by rare hybridization betweensexuals and apomicts,the latter acting aspollen donors.Less extensive clonal diversity is generatedby mutations within clonal lineages.Clonal diversity may bemaintained by frequency-dependentselection, caused by biological interactions(e.g. competitors and pathogens). Some clones are geographically widespreadand probably representphenotypically plastic ‘general-purposegenotypes’ . The long-term evolutionary successof apomictic clonesmay belimited by lack ofadaptive potential andthe accumulation ofdeleterious mutations. Although apomictic clonesmay beconsidered as ‘ evol- utionary deadends’ , thegenes controlling apomixis canescape from degenerationand extinction via pollen in crossesbetween sexuals and apomicts. In this way,apomixis genesare transferredto a new geneticbackground,