Biochemical Variation in the Black Bear

A total of 35 presumably distinct biochemical loci were analyzed in black bears (Ursus americanus) from Alaska, California, Maine, Montana, Tennessee, and Virginia by using starch-gel electrophoresis. Limited spatial subdivision of gene frequency was observed in Tennessee. Overall heterozygosity levels are lower in black bears than would generally be expected for mammalian species. Levels of interpopulation genetic similarity are extremely high for a species with such wide distribution, in contrast to the observed morphological variation. Recent efforts have been made to evaluate the potential and encourage the use of information on the genetic structure of wildlife populations (Berry 1971, Morgan et al. 1974, Smith et al. 1976). Gene frequencies change through time and space (Krebs et al. 1973, Redfield 1973, Utter et al. 1974, Berry and Peters 1976, Manlove et al. 1976) and these changes may be functionally associated with demographic changes (Smith et al. 1976). Levels of genetic variability need to be assayed to evaluate the potential use of genetic data in the formulation of a comprehensive management program. Our objective is to document levels of biochemical variability in the black bear from various populations throughout its range. Certain ecological and historical factors affect levels of biochemical variation (Selander 1976, Soule 1976) and confound the interpretation but not necessarily the application of genetic data. Low levels of biochemical variation could be due to drift or founder effect, but both of these factors imply small population numbers at some time in the past. For example, Bonnell and Selander (1974) have explained low biochemical variability in northern elephant seals (Mirounga angustirostris) by suggesting a bottleneck effect of reduced numbers resulting from their interactions with humans. Although this argument is certainly tenable, the ecological effects of low environmental variability on a large animal with high vagility might also explain the reduced variation. Animals with a large body size, great mobility, and a high level of homestatic control may be expected to exhibit low levels of genetic variability (Selander and Kaufman 1973). For a population experiencing the environment as fine-grained (i.e., apparently homogeneous), the optimum evolutionary strategy will often be a single phenotype adapted to the conditions in the environment that are most frequently encountered (Levins 1968). Valentine (1976) has predicted the occurrence of relatively low genetic variability in large migratory carnivores of the temperate zone since, by perceiving the environment as relatively fine-grained, they should have alleles whose products function under a variety of conditions. Studies of biochemical variability in mammal populations have emphasized small mammal species, and few studies exist for large carnivores. Larsen (personal communication) found no evidence of genetic variation in polar bears (Ursus maritimus), and Yang (personal communication) found low levels of variation in brown bears (U. arctos). Because of the potential use of protein polymorphisms for population studies and the lack of adequate data to verify theoretical generalizations, the assessment of genetic variation in large wildlife species such as black bears is of particular interest. The laboratory aspects of this research were supported in part by contract (AT 38-1-819) between the U.S. Energy Research and Development Administration and the University of Georgia. S. Yang, Museum of Vertebrate Zoology, University of California at Berkeley, graciously provided the supplementary data from California. D. Beeman, Graduate Program in Ecology, University of Tennessee, assisted in sample preparation. We particularly appreciate the cooperation of R. Hugie, Maine Department of Inland Fisheries and Wildlife, University of Main; C. Jonkel, School of Forestry, University of Montana; R. Modafferi, Alaska State Department of Fish and Game, Anchorage; and J. Raybourne, Staunton, Virginia, who took time and effort from the course of their own research to provide samples for this study.