Using computer simulation to assess management strategies for retention of genetic variation in captive tiger populations

Effective genetic management is essential for the maintenance of viable captive populations that can act as genetic reservoirs for species endangered in the wild. Actions that maximize retention of gene diversity often are associated with political and economic costs to zoos, requiring population managers to balance species and institutional needs. Current analytical models for projection of future gene diversity have limited utility for captive population management and do not allow for the evaluation of different management strategies. A simulation model (SIMPOP) that combines population viability analysis with genetic management was found to be a better predictor of gene diversity retention in the Amur tiger (Panthera tigris altaica) Species Survival Plan (SSP) population. Analyses using SIMPOP suggest that the Amur tiger SSP population can retain 90% gene diversity over a 100-year program without additional genetic founders. Various management strategies were evaluated for their relative effect on future gene diversity. The addition of new founders provides the greatest genetic benefit. Other management strategies that slow loss of genetic variation include increased population size, higher breeding success, and extending reproductive lifespan. Moderate relaxation of management intensity from optimal genetic management to accommodate political and economic institutional concerns did not result in a substantial reduction in gene diversity. Unlike the Amur tiger population, Sumatran (P.t. sumatrae) and Indochinese (P.t. corbetti) tiger SSP populations will require genetic supplementation to retain 90% gene diversity and reduce inbreeding. The implications of managing two vs. three tiger subspecies were discussed with respect to limited zoo resources for tigers. Recommendations for management were presented that balance genetic benefit with minimal social and economic management costs. The development of captive management programs in tiger range countries, the integration of regional captive tiger populations for optimal global management, the availability of new genetic founders for importation into the U.S., and the development of reliable and practical assisted reproduction techniques may be the major factors that will affect the future long-term genetic viability of captive tiger populations in North America.