Karyotypic Evolution in Bats: Evidence of Extensive and Conservative Chromosomal Evolution in Closely Related Taxa

Baker, R.J. , and] . 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. -Gand C-band data for seventy-eight species of bats from four families were subjected to a cladistic analysis to determine 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. [Chromosomal evolution; G-bands; rates of evolution; cladistic analysis; bats. ] In order to understand the meaning of Also, we describe and discuss a phenomchromosomal evolution. it is necessarv to enon which we call "karyotypic megahave accurate estimates of magnitude of evolution" which appears to occur not chromosomal change and documentation only in bats but in a wide variety of living of the degree to which the evolution of forms. species with differing biological characteristics has been associated with karyoMETHODS AND MATERIALS typic change. Knowledge of rates are imAll species of bats included in this reportant in the development and testing of port have been studied from Gand models of chromosomal evolution (Bush C-band preparations. Most of these e t al., 1977; Bickham and Baker, 1979; karyotypes have been described elseLande, 1979; Bengtsson, 1980). Th' is rewhere (Bickham and Baker, 1977, table port is concerned with results of G-band 1; Bickham and Hafner, 1978; Bickham, studies of the bat families Phyllostomat1979a and 197913; Bass, 1978; Baker, idae (37 species), Vespertilionidae (29 1979; Baker et al., 1979a; Johnson, 1979; species), Mormoopidae (6 species), and Patton and Baker, 1978). Noctilionidae (2 species). Approximately Within each family, chromosomal data nine percent of known bat species are inwere arranged such as to require the cluded in this r e ~ o r t . We give estimates minimum number of events derive to of magnitude of change in lineages exkaryotypes of living species. From such tending back to the hypothesized primiarrangements, it was possible to hypothtive karyotype for each family and shorter esize a primitive karyotype for each famterm estimates from congeneric species. ily (and in the case of the Phyllostomat-