RESEARCH Past hybridization betwee s Z

Full list of author information is available at the end of the articleIntroduction It is widely recognized that gene trees can differ from the species phylogeny, and gene genealogies usually proceed through various stages of non-monophyly during the early stages of their divergence history [1-6]. In a survey of published mitochondrial analyses, Funk & Omland [4] identified species-level non-monophyly in 23 % of the more than 2300 assayed species. Hybridization and in-complete lineage sorting (ILS) are considered to be two of the major, nonexclusive causes of species-level non-monophyly [4,7,8]. Hybridization between species may result in the incorporation of alleles from one species into the gene pool of another [9]. When the first gener-ation hybrids backcross with at least one of the parental species, introgression occurs. Alternatively, ILS may also result in species-level non-monophyly if species diver-gence was too recent for ancestral polymorphisms t