Chromosomes of the Townsend Pocket Gopher, Thomomys Townsendii

Abstract

Animals were collected, subjected to in vivo colchicine treatment and red bone marrow cells were stained with giemsa. Photomicrographs and karyo- grams were prepared for all seven subspecies of the Townsend pocket gopher, Thomomys townsendii. A diploid chromosome number of 76 was found for six subspecies, T. t. bachman,i T. t. elkoensis, T. t. nevadensis, T. t. owyhensis, T. t. relictus and T. t. townsendii. The seventh subspecies, T. t. similis, has a 2n chromo- some number of 40 which, along with other unique morphological traits, indicates either confusion with the Thomomys talpoides complex or consideration of taxo- nomic revision to Thomomys similis. METHODS AND MATERIALS. Chromosome preparations were made from 54 specimens of personally collected Thomomys townsendii and one specimen of Thomomys talpoides, using an in vivo colchicine treatment, femoral marrow cells and giemsa stain (Kiossoglou et al., 1964). All of the currently recognized subspecies (Hall and Kelson, 1959) were examined. Photomicrographs were made of well-spread metaphase cells, the chromosomes were cut out and hypothetically homologous pairs were matched according to size and centromere position. Accepted techniques were used to deternine chromosome number and morphology and fundamental number (Bender and Chu, 1963; Nadler and Block, 1962; Patton, 1967; Matthey, 1951). DISCUSSION. The following six subspecies, T. t. bachmani, T. t. elkoensis, T. t. nevadensis, T. t. owyhensis, T. t. relictus and T. t. townsendii, were found to have similar karyotypes and a diploid chro- mosome number of 76 as illustrated in Figures 1 and 2. In all of these the 12 metacentric chromosome pairs in Group I range uniformly from large to small, with pair number 12 relatively quite small; the 22 sub- metacentric chromosome pairs in Group II range from large to medium size, and the 3 pairs of acrocentric chromosomes in Group III range from medium-large to small size. The X chromosome is a large sub- metacentric and the Y is a small acrocenrtic (tending toward subtelo- centric in T. t. bachmani and T. t. relictus). Each of these animals has an autosomal fundamental number 142.