Wu’s genic view of speciation

Professor Wu deals almost exclusively with the ‘situation in Drosophila and more specifically the melanogaster branch of the genus’. To what extent these findings can be generalized and extended to all animals and all eukaryotes remains a question. I for one am impressed by the extraordinary diversity of speciation phenomena in animals and plants. At one extreme are the African cichlid fishes in which reproductive communities, that is biological species, are seemingly kept isolated by a few male preference genes of the females; at the other end are such cases of slow speciation as that of two diverse groups of plants. One in eastern North America, the other at the Pacific coast of eastern Asia which became geographically isolated at least 8 million years ago and yet remain members of a single species without the development of cross sterility or of taxonomic differences. Postmating isolating mechanisms are important in Drosophila but seem to be absent in certain groups of birds. Species of the duck genus Anas seem to be perfectly fertile with each other and in backcrosses although they coexist over much of the northern hemisphere with about one hybrid in 20 000 collected ducks.