Conservation Genetics of Yellowstone Bison

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Conservation Genetics of Yellowstone Bison

• October 2008
• Background
• New Research
• Principles of Conservation Genetics
• Yellowstone Bison

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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

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Background Constituency Interest

• April 2008 petition
• September 2008 IBMP Managers Meeting

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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

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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

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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

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Principles of Conservation Genetics

• 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

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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

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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

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Yellowstone Bison Population Viability

• 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.

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Yellowstone Bison Breeding Distribution

• 1 population
• 2 breeding areas

Immigration
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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 (?)

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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

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Yellowstone Bison Uncertainty

• 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

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Yellowstone Bison Continuing Workat University
of Montana

• 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

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Questions?