Rapidly evolving repetitive DNAs in a conservative genome: a test of factors that affect chromosomal evolution

The hypothesis that tandemly repeated DNA sequences may facilitate chromosomal rearrangements was tested by comparing a conservatively evolving karyotype of a bat species (Macrotus waterhousii) with data published for a rapidly evolving karyotype of an equid species (Equus zebra). Empirical data generated from the phylogenetic screening of rapidly evolving repetitive DNAs from approximately 0.1% of the M. waterhousii genome showed only one sequence that was repetitive in M. waterhousii but low in copy number or absent from the outgroup Artibeus jamaicensis. This compares to 34 such clones containing sequences which were repetitive in E. zebra but were low in copy number or absent from the outgroup Ceratotherium simum. The bat sequence represents a single family of repeated sequences, whereas six families of sequences were identified in E. zebra. Southern blot analysis suggested that the sequence from M. waterhousii is interspersed rather than tandemly repeated, as are the sequences in E. zebra, These data support the above hypothesis and suggest that species with conservatively evolving karyotypes have fewer numbers and families of rapidly evolving DNA sequences than do species such as the equids that possess a karyotype that is considered to have undergone rapid karyotypic evolution.