Baker, R.J., a n d ] . W . Bickha,m (The Museum and Department of Biological Sciences, Texas Tech University, Lubbock, Texas 79409 and Department of Wildlife and Fisheries Sciences, Texas A and M University, College Station, Texas 77843) 1980. Karyotypic evolution in bats: evidence of extensive and conservative chromosomal evolution in closely related taxa. Syst. Zool., 29:239-253.-G- and C-band data for seventy-eight species of bats from four families were subjected to a cladistic analysis to

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... etermine the number of chromosomal rearrangements required to convert the karyotype proposed as primitive for a family into the karyotype of extant species in that family. The number of rearrangements ranged from 0 to 36, and if the age of families is 60 million years, average rate of incorporation of rearrangements per million years ranged from 0 to 0.6. When chromosomal variation in congeneric species were subjected to a similar-dadistic analysis, most (34 of 54) species had undergone no chromosomal rearrangements; however, some species had undergone from 14 to 20 rearrangements and the types of rearrangements that were incorporated in species having the largest amount of change were generally rearrangements that should produce considerable reduction in gamete fertility in individuals heterozygous for such rearrangements. Radically reorganized karyotypes appear not only in bats but in a wide variety of vertebrates. Factors related to demography, breeding structure, and speciation do not appear adequate to explain the occurrence of such radically reorganized genomes. Factors less related to demographic and vagility characteristics, such as mutation rate and mechanisms which reduce the meiotic constraints on the heterozygote, are phenomena which may be involved in evolving a radically reorganized karyotype.