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Questions?. Genetic variation & inbreeding. Genetic Variation. “Genetic variation is the stuff of diversification, of adaptation, of speciation, of evolution: without it, a population or species lacks the raw material to respond to changing conditions.” L. Scott Mills. Motivating Examples.

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genetic variation
Genetic Variation

“Genetic variation is the stuff of diversification, of adaptation, of speciation, of evolution: without it, a population or species lacks the raw material to respond to changing conditions.”

L. Scott Mills

florida panthers
Florida Panthers
  • Isolated for >100 years
  • Major bottleneck (30-50 individuals)
  • Breakdown in typical dispersal strategies
florida panthers1
Florida Panthers
  • Inbreeding depression
greater prairie chicken
Greater Prairie Chicken
  • Populations in Illinois were reduced by loss of habitat farmland.
slide9
1962 – 2000 birds  1994 population was <50.

Population declined despite efforts to control predators and increase quality and quantity of habitat.

DNA from this population showed a decrease in genetic variation compared with museum specimens from the 1930s and contemporary large populations.

50% of eggs failed to hatch, suggesting fixation of harmful alleles.

Mechanisms of Evolution – genetic drift

greater prairie chickens genetic rescue
Greater prairie chickens – Genetic rescue
  • 1992 – 1996 birds from MN, KS, NE translocated to IL population
  • Translocations of prairie chickens from neighboring states increased low egg fertility and hatching success
  • HOORAY! But the final moral of the story was…
but lots of contradictory examples
But lots of contradictory examples…
  • Elk, deer, pronghorn, bison, turkeys
    • Faced huge bottlenecks
    • Restricted to a few remnant populations
    • Rebounded to staggering numbers!
  • What was different for these species?
slide12

Desert pupfish

    • Small isolated populations are the norm for pupfish
so what matters
So what matters?
  • Genetic Variation
  • Effective population size
    • And the number of generations spent at small Ne
  • Connectivity
hardy weinberg equilibrium1
Hardy-Weinberg equilibrium
  • Observed heterozygosity
  • Expected heterozygosity
a quick exercise
A quick exercise
  • Work in pairs
  • Start with 2 individuals in a population both heterozygotes
  • Flip a coin to determine alleles passed on to the next generation (2 offspring per generation)
  • Proceed for 6 generations or until the alleles are fixed
  • What are the allele frequencies?
what affects genetic variation
What affects genetic variation?
  • Mutation
  • Gene flow
  • Natural selection
  • Genetic drift
genetic drift
Genetic Drift
  • Random change in allele frequencies in small population
  • Causes populations to diverge
measuring genetic drift
Measuring Genetic Drift
  • Effective population size
    • Equivalent number of individuals if all members of the population were randomly mating
    • Ne < N
    • Often ~0.2-0.3 for wildlife
    • Sometimes much smaller
effective population size
Effective population size
  • Contributing factors
    • Breeding sex ratio
    • Fluctuations in population size
    • Variance in family size
variance in population size
Variance in Population Size
  • We’ve seen arithmetic means and geometric means, now harmonic mean
fragmentation
Fragmentation
  • Founder Effects
    • Reintroductions
    • Translocations
  • Genetic drift at work in the background
inbreeding
Inbreeding
  • Inbreeding coefficient
    • F
      • I – individual
      • S – subpopulation
      • T – total population
inbreeding1
Inbreeding
  • FIS - inbreeding of an individual relative to its subpopulation
    • Typically near 0
  • FST - inbreeding of subpopulation relative to the total
    • Loss of diversity due to drift
inbreeding3
Inbreeding

Subpopulation heterozygosity

Total expected heterozygosity

inbreeding5
Inbreeding

Ne= 100

inbreeding depression
Inbreeding depression
  • Does it occur?
inbreeding depression1
Inbreeding depression
  • Does it occur?
    • Yes
  • Does it reduce vital rates?
inbreeding depression2
Inbreeding depression
  • Does it occur?
    • Yes
  • Does it reduce vital rates?
    • Sometimes
  • Do reduced vital rates = reduced lambda?
outbreeding depression
Outbreeding depression
  • Potential loss of local adaptation
genetic rescue
Genetic Rescue
  • Increased fitness following the arrival of new genes
  • Breaks deleterious effects of inbreeding
migration
Migration
  • Not movement, not this time
  • The transfer of genes from one population to another
  • AKA Gene flow
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