Chain Processes in Chromosomal Speciation

Abstract

<it>White,M.J. D. (Department of Population Biology, Research School of Biological Sciences, Australian National University, P.O. Box 475 Canberra City, ACT, 2601. Australia) 1978. Chain processes in chromosomal speciation. Syst. Zool. 27:285–298</it>.—In many groups of animals of restricted vagility very closely related species not only differ in karyotype, but exhibit very extensive differences, due to the establishment of “chains” of several or many structural chromosomal changes. These cases, which until recently appeared anomalous or inexplicable, can now be used to interpret a basic feature of the “stasipatric” mode of spe-ciation (parapatric speciation of some authors). It is suggested that an important reason for the establishment of these chromosomal rearrangements is their role in protecting coadapted gene complexes (“area effects”) from disruption by introgression from neighboring populations. A model, based on the mouse (<it>Mus musculus</it>) populations of Italy and Switzerland studied by E. Capanna, A. Gropp, and their collaborators, is proposed; it relies on sequential establishment of chromosomal rearrangements, each within the range of the previous one. By this means the genetic isolation of the area population is progressively reinforced.