EXTREME CHROMOSOMAL POLYTYPY IN A POPULATION OF SCELOPORUS-GRAMMICUS (SAURIA, PHRYNOSOMATIDAE) AT SANTUARIO-MAPETHE, HIDALGO, MEXICO

The karyotypic status of the mesquite lizard, Sceloporus grammicus, wa s investigated at two localities at Santuario Mapethe, Hidalgo, Mexico . A total of 23 different karyotypes was recorded from the 36 individu als examined. individual lizards were heterozygous at up to four chrom osomes. Karyotypic differences were attributed to Robertsonian fission /fusions and pericentric inversions involving the macrochromosomes. Th e polymorphisms generally conformed to Hardy-Weinberg equilibrium sugg esting a lack of underdominance for most rearrangements. The extreme c hromosomal polytypy observed at Santuario Mapethe is hypothesized to r esult from parapatric hybridization between two chromosome races.