Chromosomal and Genetic Divergence in the Fossorial Lizards of the Family Anniellidae

Abstract

Bezy, R. L., G. C. Gorman, Y. J. Kim, and J. W. Wright (Section of Herpetology, Natural History Museum of Los Angeles County, Los Angeles, Califomia 90007 [Bezy and Wright]; Department of Biology, University of California, Los Angeles, California 90024 [Gorman and Kim]) 1977. Chromosomal and genetic divergence in the fossorial lizards of the family Anniellidae. Syst. Zool. 26:57-71.-Chromosomal divergence within the family Anniellidae is extensive. Diploid chromosome numbers in somatic tissue range from 36 in Anniella geronimensis to 22 in northern and 20 in southern A. pulchra. One to four testicular supernumerary microchromosomes occur in A. p. pulchra populations in northern Baja California. There is a lack of congruency between the chromosomal and morphological races of A. pulchra. Within the infraorder Anguimorpha, anniellids have chromosomal similarities to both the diploglossans (Anguidae) and the platynotans (Varanidae). The genetic distances between the four populations of Anniella analysed electrophoretically correspond well with their currently recognized hierarchical relationships: DN = .282-.298 between the two species, .104-.119 between the two subspecies, and .003 between populations within subspecies. In comparison to other sympatric congeneric species of amphibians and reptiles, A. pulchra and A. geronimensis are only moderately divergent genetically. The genetic distance between populations of A. pulchra which differ in somatic karyotype is greater than that between the populations which differ only in supernumerary chromosomes. Allelic heterozygosity in populations of Anniella is notably low (ca. 1%). This low level of genetic variability and high level of chromosomal divergence accompanied by relatively few structural genomic changes appear to be important evolutionary correlates to the fossorial life-style of anniellid lizards. [Karyotypes; genetic divergence; Anniellidae; Sauria.] The family Anniellidae is composed of three taxa of legless, fossorial, anguimorphan lizards occurring in California and northern Baja California (Fig. 1-2; McDowell and Bogert, 1954; Wermuth, 1969). Anniella pulchra Gray 1852 ranges from Antioch, Contra Costa Co., California, south to Bahia San Quintin, Baja California del Norte, its seemingly disjunct populations occurring most extensively in coastal sand dunes, but extending inland to the Colorado Desert and the western slope of the Sierra Nevada (Shaw, 1953; Stebbins, 1954). A dark race, A. p. nigra Fischer 1885, occurs primarily on the humid Monterey Peninsula of California, all other populations of the species being currently assigned to the lighter typical form, A. p. pulchra. Anniella geronimensis was originally described from Isla San Geronimo (Shaw, 1940) and subsequently reported on the adjacent mainland of Baja Califor nia del Norte (Shaw, 1949), where it was ultimately discovered to be sympatric with A. pulchra (Shaw, 1953). Karyotypic differences between populations of A. pulchra were reported previously (Bezy and Wright, 1971; Gorman, 1973). We here describe the karyotype of A. geronimensis and additional populations of A. pulchra, present electrophoretic data on coastal populations of the three nominate taxa, and discuss genetic and chromosomal variability and divergence in relation to the ecology and evolution of the lizards of the family. MATERIALS AND METHODS Chromosomes were prepared by a colchicine, hypotonic citrate technique (Patton, 1967; Lowe, Wright, and Cole, 1966), using heterogeneous tissue samples