QUANTITATIVE ANALYSIS OF KARYOTYPE ALTERATION AND SPECIES DIFFERENTIATION IN MAMMALS.

Abstract

Recent advances in mammalian cytogenetics have revealed that (1) most morphologically distinctive species are karyotypically differentiated (see the chromosome monographs by Hsu and Benirschke, 1967-1975), and (2) there are some species which include karyotypically highly diversified local populations, for example, Mus musculoides (Jotterand, 1972; Matthey, 1973), Mus poschiavinus (Gropp et al., 1972), Spalax ehrenbergi (Wahrman et al., 1969), and Thomomys bottae grahamensis (Patton, 1970). These accumulated data seem to be consistent with the stasipatric speciation model proposed by White (1968, 1978) based on the karyotype analysis of morabine grasshoppers. According to the model, chromosome rearrangements are considered to have played an essential role in speciation as one of the isolation mechanisms. On the other hand, there are also indisputable reports that morphologically distinct species sometimes have apparently identical karyotypes, for example, in Canis (Wurster and Benirschke, 1968), Macaca (Egozcue, 1975), and Myotis (Baker, 1970), suggesting speciation without visible karyotype differentiation. This conflicting evidence may be reconciled, however, by postulating two types of speciation, one with and one without karyotype differentiation. In this case, the role of karyotype alteration in species differentiation should be solved in a quantitative framework. I attempt in the present paper to investigate quantitatively the relationship between karyotype alteration and species differentiation in mammals by analyzing the number of karyotypes and species per genus. ANALYSIS