| The caribou (Rangifer tarandus) has been the most valuable game species throughout circumpolar regions since ancient times. They have remained an important economic and cultural resource for northern communities. However, caribou are not always a dependable resource, due to marked population declines and range shifts that occur at unpredictable intervals. These fluctuations are often caused by harsh environmental conditions. In addition, since the early 19th century, many caribou herds have experienced various levels of stress due to human encroachment on caribou ranges. Consequently, a number of populations and subspecies have recently been listed as threatened or endangered. As herd range conditions change with increased land use, maintenance of existing genetic diversity will become more difficult. Genetic diversity is necessary for a population to adapt to changes in environmental conditions and can reduce the risk of inbreeding effects. Consequently, it is important to determine current levels of diversity within herds and identify herds that require additional management attention. Furthermore, understanding caribou population genetic structure is important, as management decisions affecting one herd may have profound effects on related herds. This study describes the examination of microsatellite DNA to estimate existing genetic variation and to determine the population genetic structure among North American caribou herds. Genetic diversity data were also used to evaluate the applicability of subspecies designations for defining units at which conservation should be directed.; Despite recent population fluctuations and declines, genetic diversity was high for most North American caribou herds, suggesting that they are not currently at risk of inbreeding depression. For most caribou subspecies, diversity levels reflected their degree of isolation from other herds. These data were used to identify benchmarks for genetic diversity levels in caribou herds that have experienced opposite extremes of habitat fragmentation: those that have remained relatively undisturbed by habitat change and habitat fragmentation, and those that are in imminent danger of extinction due to severe habitat loss and population declines. The results presented here provide a genetic basis for understanding caribou population dynamics and can be useful for future assessments of the genetic health of caribou, and for conservation and management efforts. |
