Questions?

1. Questions?

2. Genetic variation & inbreeding

3. 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

4. Motivating Examples

6. Florida Panthers • Isolated for >100 years • Major bottleneck (30-50 individuals) • Breakdown in typical dispersal strategies

7. Florida Panthers • Inbreeding depression

8. Greater Prairie Chicken • Populations in Illinois were reduced by loss of habitat farmland.

9. 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

10. 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…

11. 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?

12. Desert pupfish • Small isolated populations are the norm for pupfish

13. So what matters? • Genetic Variation • Effective population size • And the number of generations spent at small Ne • Connectivity

14. Hardy-Weinberg equilibrium i

15. Hardy-Weinberg equilibrium • Observed heterozygosity • Expected heterozygosity

16. 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?

18. What affects genetic variation? • Mutation • Gene flow • Natural selection • Genetic drift

19. Genetic Drift • Random change in allele frequencies in small population • Causes populations to diverge

20. 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

21. Effective population size • Contributing factors • Breeding sex ratio • Fluctuations in population size • Variance in family size

22. Ne and Sex ratio

23. Variance in Population Size • We’ve seen arithmetic means and geometric means, now harmonic mean

24. Fragmentation • Founder Effects • Reintroductions • Translocations • Genetic drift at work in the background

25. Inbreeding • Inbreeding coefficient • F • I – individual • S – subpopulation • T – total population

26. 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

27. Inbreeding

28. Inbreeding Subpopulation heterozygosity Total expected heterozygosity

29. Inbreeding

30. Inbreeding Ne= 100

31. Inbreeding depression • Does it occur?

32. Inbreeding depression • Does it occur? • Yes • Does it reduce vital rates?

33. Inbreeding depression • Does it occur? • Yes • Does it reduce vital rates? • Sometimes • Do reduced vital rates = reduced lambda?

34. Positive effects of inbreeding? • Purging

35. Outbreeding depression • Potential loss of local adaptation

36. Genetic Rescue • Increased fitness following the arrival of new genes • Breaks deleterious effects of inbreeding

37. Migration • Not movement, not this time • The transfer of genes from one population to another • AKA Gene flow

38. Next: Connectivity