Conservation Genetics of Yellowstone Bison

October 2008

• Background

• New Research

• Principles of Conservation Genetics

• Yellowstone Bison

Background : IBMP

• IBMP includes a minimum population abundance to meet the conservation objective

• Genetic integrity conserved by “balancing a minimum late-spring population of 3,000 animals with other objectives

• Acknowledged uncertainty

• Committed to procuring additional information

Background : Constituency Interest

• April 2008 petition

• September 2008 IBMP Managers Meeting

New Research : Halbert 2003

• No evidence of cattle hybridization

• High levels of diversity relative to other federally managed bison herds

• Genetic sub-division but not true subpopulations

• Evidence of removing parents and off-spring - Consequences of this non-random removal need

further investigation

New Research : Gross et al 2006

• Population viability relative to heterozygosity (He), allele retention, and demographic structure

• Examined effects of variety of removal strategies used by NPS bison managers

• Population size provides best mechanism to preserve genetic diversity

New Research : Gardipee 2007

• New methods to study bison genetics during breeding season

• mtDNA haplotype data shows population subdivision among breeding groups

• Microsatellite analyses continuing

• Genetic processes occur slowly. Diversity is maintained through natural selection (random mating) and mutation

• Large populations can maintain diversity in isolation, while small populations need a small amount of gene flow (immigration)

• Retaining adequate genetic diversity (i.e., alleles) is necessary for bison to adapt to a changing environment

Principles of Conservation Genetics

• Removing individuals eliminates their genetic input to the population genome

• Sustained high rates of mortality can reduce genetic diversity

• Removal strategies that maintain natural age and sex structure will minimize consequences

Principles of Conservation Genetics

• Maintenance (or rate of loss) of diversity is affected by generation time and population size

• Maintaining diversity in Yellowstone bison depends on maintaining adequate abundance in the central and northern breeding groups

• MVP PVA

Principles of Conservation Genetics

• Conservation of a bison population with 2,500 – 4,500 individuals (i.e., 1,000 to 2,000 bison in each of the central and northern herds) should retain 90-95% of genetic diversity in Yellowstone bison over the next 200 years.

Yellowstone Bison : Population Viability

Yellowstone Bison : Breeding Distribution

•1 population

•2 breeding areasImmigration

Yellowstone Bison: Genetic Structuring

• Herd differences likely reflect population bottleneck that occurred 100 years ago and the initial isolation of endemic and reintroduced herds

• Fidelity to breeding areas is strong (♀)

Yellowstone Bison: Susceptibility

• Heavily skewed sex ratios lead to non-random mating

• Brucellosis risk management operations can result in …

- large variations in breeding group size through disproportionate removals

- disproportionate removal of females

• Genetic sub-division within the population

• Rates of gene flow between breeding groups

• Precisely how brucellosis risk management removals may affect conservation of genetic diversity

Yellowstone Bison: Uncertainty

• Micro-satellite estimates to quantify current diversity values and gene flow

• Simulation modeling to evaluate affects of brucellosis risk management removals

• Estimation of census population size necessary to maintain diversity values

• Recommended monitoring strategy to detect changes in diversity values

Yellowstone Bison: Continuing Workat University of Montana

Questions?