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How small can a population get before inbreeding becomes intolerable?

How small can a population get before inbreeding becomes intolerable?. Formulas first:. If F = 1 and N e = 4 M F 2N e M + F Then F = 1 and F = 1 + 1 2 4 M F 8F 8M M + F. Important!. 60a.

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How small can a population get before inbreeding becomes intolerable?

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  1. How small can a population get before inbreeding becomes intolerable? Formulas first: If F = 1 and Ne = 4 M F 2Ne M + F Then F= 1 and F =1 + 1 2 4 M F8F 8M M + F Important! 60a

  2. How small can a population get before inbreeding becomes intolerable? F =1 + 1 8F 8M Research on domestic farm animals: natural selection for performance can balance inbreeding depression if the ΔF is no more than 1% per generation. So, F = 0.01 is a tolerable level of inbreeding 60a

  3. How small can a population get before inbreeding becomes intolerable? F =1 + 1 8F 8M If F = 0.01 is a tolerable level of inbreeding, then .01 = 1 + 1 so F = 25 and M = 25 8F 8M or, Ne = 50 Magic number! 60a

  4. What happens to the ‘magic number’ when sex ratios are unequal? 1 1 8Nm 8Nf F = + Conclusion: 15 = smallest number of effective individuals of one sex Number of females .005 tolerance 25 .01 tolerance 15 25 Number of males 60

  5. Population bottlenecks bottleneck Population size Time H = 1 - 1 = expected proportion of Ho retained after a 2Ne 1-generationbottleneck Ht = Ho 1 - 1 t = proportion of Ho retained t generations after 2Ne a bottleneck if Ne = 4 at t=0, then Ht=1 = 1 - 1 = 7 i.e. 1/8 of original H 2 x 4 8 was lost in 1 generation 61A

  6. The effect of bottlenecks on H Proportion of original heterozygosity remaining in small populations 61-1

  7. Probability of retaining a rare allele after a bottleneck of size N for a single generation 1.0 q = .10 q = .05 Probability of retention q = .01 0 0 25 Population size (Ne) 61-2

  8. Conclusions: Effects of Inbreeding and Bottlenecks  H P --------------------- ------------------- Bottleneck: decreases by 1/2Ne LARGE decrease with reproduction especially of rare alleles Inbreeding: LARGE decrease no change 65

  9. Effects of a genetic bottleneck in a plant: Lakeside daisy (Hymenoxys acaulis) - only one population survived agricultural development - self-incompatibility - requires mates of a different mating type -but alleles for only one mating type survived the bottleneck…..

  10. Founder Effect (Founders) Speke’s gazelle zoo Wild population Founders to zoo in 1970s: 1 male, 3 females N = 4, but Ne = 2 Initial severe inbreeding In 1982, N = 29 Inbreeding depression eliminated. Escaped F - vortex? 65A

  11. Contribution of 16 founders to the captive Guam Rail population 20 15 % Founder contribution 10 Expected 1/16 = .0625 5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 31 32 33 36 98 Founders 65e

  12. Speke’s gazelle http://www.ultimateungulate.com/gazellespeke.html

  13. Okapi http://www.ultimateungulate.com/okapi.html

  14. Goeldi's monkey and Okapi • 40% loss of genetic diversity in captive populations • due to unequal founder contribution • Drosophila on Hawaiian Islands • 95 of 100 species are endemic to only one island or • volcano (results of migration of single, fertilized • “eves”)

  15. Population Management: Founder Effect founders Wild population Problem: Founding event--> forced inbreeding --> inbreeding depression Best Solution: MAXIMIZE GROWTH OF THE POPULATION A.S.A.P.!! 65A

  16. What is the minimum Nenecessary to maintainevolutionary potential??? 500 The other magic number Selection balances Drift…..Maybe!!!!

  17. The Biology of Small Populations • Population Dynamics of Small Populations • Genetics • Population Viability Assessment • The Ecology of Conservation and Extinction

  18. Minimum Viable Population • First stab: 50 / 500 rule. • John James Audubon – the first PVA

  19. Mauritian Kestrel 1970’s: Rarest bird in the world!

  20. Triage • Triage: Sorting the casualties of war into those too badly wounded to recover, those who can survive without help, and focusing on the remainder.

  21. Triage Conservation Biology • “We might abandon the Mauritius kestrel to its all-but-inevitable fate, and utilize the funds to proffer stronger support for any of the hundreds of threatened bird species that are more likely to survive” - Norman Myers, The Sinking Ark

  22. There are no hopeless cases, only people without hope and expensive ones – Michael Soulé Hopeless Cases?

  23. But . . . • The Mauritius kestrel was never exceptionally common • The fact still remains that we have limited resources to allocate to many species • 10 million $ to rent a Panda

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