Rates of karyotype evolution in placental mammals

The genera of eutherian mammals have been divided into two groups depending on whether the animals in the genera have high or low rates of karyotype evolution. The rate of karyotype evolution in a genus is estimated by the standard deviation of the chromosome numbers within the genus. The estimates have been found to correlate with the size of the animals and the taxonomic diversity of the genera: small animals have a higher rate of karyotype evolution than large animals, and animals belonging to genera with many taxa have a higher rate of karyotype evolution than animals belonging to genera with few taxa. No correlation has been found between the chromosome number and the rate of karyotype evolution. The analyses are made by comparing genera which belong to the same taxonomic family. Our results are consistent with the results obtained by A. C. Wilson, G. Bush and their co‐workers using different methods of estimation and comparison. The correlations between size, taxonomic diversity and rates of karyotype evolution are discussed in the light of results from theoretical models describing the spread of chromosome mutations in populations. Particular attention is given to the role reproductive biology may play in influencing the rate of karyotype evolution.