The Relationships of the Anolis of the Roquet Species Group (Sauria: Iguanidae). II. Comparative Chromosome Cytology

Abstract

Karyotypic data are presented for members of the Lesser Antillean Anolis of the roquet group, and their geographic near neighbors. The roquet group is characterized by six pairs of metacentric macrochromosomes. The near neighbors to the south (A. chrysolepis) and west (A. lineatus) have seven pairs of macrochromosomes. The species to the north, A. octulatuis, has a distinctly different karyotype, with no sharp distinction between macrochromosomes and inicrochromosomes, and shows male chromosomnal heteromorphism. Within the roquet group, five forms have 12 pairs of microchromosomes, and three forms have 11 pairs. The latter is considered a specialized condition that only arose once within the group and is indicative of close taxonoinic relationship. For the student of vertebrate evolution, the New World lizard genus Anolis is a most convenient group. The numerous species, numbering approximately 200, are often abundant and easily obtained. Many are endemic to single island banks in the Caribbean, and detailed analyses of the relationships of these island forms can tell us much about evolutionary patterns in the characters that we choose to study, as well as about evolution in the lizards themselves. This is particularly true for Anolis because the broad patterns of evolution have been well worked out in an osteological study (Etheridge, 1960). Etheridge divides Anolis into two major groups, termed alpha and beta, and subdivides these groups into species series. The alpha group is predominantly South American and Antillean and seems to have moved secondarily into Central America as far north as Costa Rica. The beta group is primarily Mexican and Central American which radiated into South America, several of the islands adjacent to the Venezuela mainland, Jamaica, Cuba, and the Bahamas. A preliminary study of the chromosomes of nine species of Anolis (Gorman, 1965) suggested that karyotypes would be a valuable character in the study of Anolis evolution. As in many reptiles and birds, the chromosomes of Anolis of many species fall into two sharply defined size classes termed macrochromosomes and microchromosomes (see Matthey, 1949 for general review). Gorman characterized beta anoles as having 14 macrocbromosomes. Alpha Anolis of several species series have 12 macrochromosomes, while in the bimaculattis series there is no sharp break between macrochromosomes and microchromosomes. In this series of species, Gorman and Atkins (1966) have described male chromosomal heteromorphism. Several members of the bimaculatus species series were examined; in all males 2n= 29 and in females 2n= 30. Both sexes have three pairs of large metacentric macrochromosomes, three pairs of large submetacentric chromosomes, three pairs of small metacentrics (approaching microchromosomes in size), and four pairs of microchromosomes (i.e., 26 autosomes). Males have three morphologically unpaired ehromosomes: an acrocentric (X1), a microchromosome (X2), and a small metacentric (Y). These form a trivalent at meiosis. The female formula may be expressed