Rapid speciation and chromosomal evolution in mammals.

Abstract

To test the hypothesis that population subdivision into small demes promotes both rapid speciation and evolutionary changes in gene arrangement by inbreeding and drift, rates of speciation and chromosomal evolution in 225 genera of vertebrates was estimated. Speciation rates were estimated by considering the number of living species in each genus and fossil record of each genus as well as information about extinction rates. Speciation rate was strongly correlated with rate of chromosomal evolution and average rates of speciation in lower vertebrate genera were 1/5 those in mammalian genera. Genera with high karyotypic diversity and rapid speciation rates may generally have small effective population size (Ne), whereas large Ne values may be associated with karyotypically uniform genera and slow rates of speciation. Speciation and chromosomal evolution seem fastest in those genera with species organized into clans or harems (e.g., some primates and horses) or with limited adult vagility and juvenile dispersal, patchy distribution and strong individual territoriality (e.g., some rodents), consistent with this hypothesis regarding the evolutionary importance of demes.