Morphometrics, Evolution, and Cytotaxonomy of Mainland Bats of the Genus Macrotus (Chiroptera: Phyllostomatidae)

Davis, Brent L., and Robert J. Baker (Dept. Biology, and The Museum, Texas Tech University, Lubbock, Texas) 1974. Morphometrics, Evolution, and Cytotaxonomy of Mainland Bats of the Genus Macrotus (Chiroptera: Phyllostomatidae). Syst. Zool. 23:26-39.-Chromosomal data reveal the existence of two mainland species of Macrotus that are parapatric in distribution. Individuals can be identified to species by both chromosomal features and cranial morphology. A stepwise multiple discriminant analysis and canonical variate analysis show that the two species are morphometrically divergent. The distribution of these two taxa is proof that parapatry occurs in species with high vagility. If chromosomal data had not been available or if chromosomal divergence had not accompanied speciation in Macrotus, this unique pattern of distribution probably would not have been detected. Allopatric, stasipatric, and centrifugal speciation are considered in light of the presently available data for Macrotus. [Macrotus; morphometrics; cytotaxonomy.] Geographic variation in chromosome number is rather uncommon among bats of the family Phyllostomatidae. Of the 77 species of phyllostomatids thus far karyotyped (Baker, 1973), four species show geographic variation-Uroderma bilobatum (Baker et al., 1972), Macrotus waterhousii (Nelson-Rees, et al., 1968), and Micronycteris hirsuta and Vampyressa pusilla (Baker et al., 1973). Chromosomal variation in Macrotus, which previously was thought to have two chromosomal races, is of the Robertsonian type (the fundamental number remains constant but the diploid number varies). The cytotype with a diploid number (2N) of 46 and a fundamental number (FN) of 60 has been reported as having a geographic range from Alamos, Sonora, south through Morelos, and Guerrero (Nelson-Rees et al., 1968). The 2N = 40, FN = 60 cytotype had a known distribution from Carbo, Sonora, north to Arizona and California. Alamos (the most northern published record for the 2N = 46 cytotype) is 335 kilometers south of Carbo (the most southern reported locality of the 2N = 40 cytotype). Variation in diploid number, as understood at the outset of this study, was confined to the subspecies M. w. californicus (Anderson, 1968, 1969; Nelson-Rees, et al., 1968). The primary reason for studying the cytogenetics and morphometrics of Macrotus was to determine the mechanism of evolution and the degree of hybridization between the two cytotypes. Robertsonian variation is the most likely mechanism by which a chromosomal change of this nature could occur (Nelson-Rees et al., 1972). If centric fusions or fissions are the mechanism by which the cytotypes evolved, loss or gain of genetic material probably would have occurred in the heterochromatic region (Jackson, 1971) and a cross between the two cytotypes should be successful, at least on a chromosomal basis of homology. Because of the relative ease with which specimens of Macrotus can be obtained and because the species is chromosomally variable, detailed studies were initiated. Several possibilities are obvious from the outset. First, the two cytotypes could be freely interbreeding. If this were the case, the genetics of the system could be examined by using chromosome number, morphology, and meiotic studies. Second, the two could be sympatric and produce no hybrids. Third, the two could have allopatric distributions. Our studies have revealed a parapatric distribution (as discussed for mammals by Vaughan, 1967) with no phenetic inter-