The role of chromosomal rearrangement in mammalian speciation with special reference to Cetacea and Pinnipedia

Abstract

The karyotypes of 17 cetaceans and 18 pinnipeds are surveyed. Within the Cetacea only two different chromosome numbers have been found, viz. 2n = 42 and 2n = 44. Within the Pinnipedia three different chromosome numbers have been described, viz. 2n = 32, 2n = 34 and 2n = 36. The material indicates that the orders Cetacea and Pinnipedia are characterized by a remarkable stability of their karyotypic patterns. Factors cooperating towards karyotypic stability may be sought in the reproductive biology of these animals — late sexual maturity and small progeny — as well as in their ecology — good mobility in an environment without distinct niches. In such animals, the main mode of speciation should be a allopatric. The orders Insectivora and Rodentia on the other hand which both display great karyotype variability would accordingly represent a different mode of speciation. The species belonging to these orders have early sexual maturity and large progeny; their mobility is often limited and the distribution discontinuous. Consequently, in Insectivora and Rodentia stasipatric speciation should be frequent.