THE ROLE OF HYBRIDIZATION AND INTROGRESSION IN THE DIVERSIFICATION OFANIMALS

Although hybridization and introgression have been considered importan t in generation of plant diversity, their role in evolutionary diversi fication of animals remains unclear. In this review, we reconsider the significance of introgressive hybridization in evolution and diversif ication of animals to determine if the generally negative assessment o f these processes is warranted. Unlike the situation for plants, hybri d animal taxa appear to be relatively rare. This could, however, be du e to negative attitudes toward hybridization and difficulty in detecti ng such forms. Hybridization has been responsible for instantaneous cr eation of several unique complexes of polyploid and unisexual animals. Allopolyploidy has allowed for diversification, whereas unisexual tax a have acted as conduits of gene exchange among related sexual species . Many instances of diploid, bisexual taxa of hybrid origin have been put forward, but few have been carefully tested. Changing attitudes to ward hybrids and technological advances should allow for careful consi deration of hypothesized hybrid taxa and will undoubtedly increase the number of known animal hybrid taxa.