Chromosome Variation in North American Fence Lizards (Genus Sceloporus; Undulatus Species Group)

Abstract

Cole, Charles J. (Dept. of Herpetology, American Museum of Natural History, Central Park West at 79th Street, New York 10024) 1972. Chromosome variation in North American Fence Lizards (Genus Sceloporus; undulatus species group). Syst. Zool. 21:357-363.Five species of lizards in the undulatus species group of the genus Sceloporus have generally similar karyotypes with a diploid number of 22 chromosomes. Nevertheless, extensive variation occurs in centromere position on pair number 7. Comparisons of chromosomes in population samples from numerous localities across North America reveal considerably more variability and kocal differentiation than is expected on the basis of current taxonomy. Intraspecific and intrasubspecific differences within the species S. undulatus often are greater than interspecific differences. Within most local populations, however, 7 occurs in a fixed (homozygous) state, as a metacentric, submetacentric, subtelocentric, or telocentric pair. Thus, individually recognizable chromosomes occurring in lizards in adjacent populations can serve as genetic markers to document interbreeding between distinctive chromosome races and improve our understanding of the evolution, systematics, and population genetics of these terrestrial vertebrates. [Sceloporus; chromosomes.] Fence lizards are well-known reptiles that abound in much of the United States and Mexico. These species and their closest relatives comprise the undulatus species group of the large and diversified iguanid genus Sceloporus. Five species (including 15 species and subspecies) currently are recognized in the undulatus group: ScelopQrus undulatus (Latreille), S. cautus Smith, S. occidentalis Baird and Girard, S. virgatus Smith, and S. woodi Stejneger (Smith, 1939, 1946; Lowe and Norris, 1956; Maslin, 1956; Cole, 1963).1 The combined geographic ranges of these species incorporate approximately three-fourths of the continental United States south of Canada and most of the northern half of Mexico. Local populations within this area are adapted to a wide variety of habitats, including desert, grassland, woodland, chaparral, and forest. The present cytological investigation was undertaken as an attempt to improve our 1 A sixth species, Sceloporus exsul, recently was described by Dixon, Ketchersid, and Lieb (1972). Chromosomes of this species have not yet been examined. understanding of the evolution and relationships of the fence lizards. Comparisons of chromosomes from individuals representing both sexes of each species and nearly all the subspecies in the group has revealed a much greater potential for analyzing relationships between local populations than had been anticipated.