1. Lecture 5: Unit of Selection Who/what benefits from adaptation? Nucleotide – Gene – Cell – Organism – Group – Species What is the unit of selection? Can a benefit at one level be detrimental to other levels? Conflict?

2. Examples Segregation distorter genes –Benefit one gene at expense of others Cell lines vs. rest of body –Must be able to reproduce from >1 cell line –Theoretical at the moment

3. Reproductive Restraint (Group Benefit) NS: allele  in freq if bearer  fitness vs. those w/o the allele NS = maximization of reproduction Why repro restraint? altruism? Conflict b/w ind. benefit & other levels?

4. Interdemic/ Interpopulational Selection VC Wynne-Edwards: Non-breeding in seabirds – how explain? NS acts on the level of group Social behaviour regulates pop’n density

5. Reproductive restraint Evidence: Northern Flicker : avg: 6-8 eggs can lay up to 71

6. Altruism Detriment to ind. fitness for benefit of others Florida Scrub Jay -young, sexually mature helpers

7. Infer: restraint evolves through pop’n selection not ind. selection Why? Unrestrained pop’n growth depletes resources & leads to extinction Implication: selection operates to the detriment of the ind. but benefit of the group How likely is this really?

8. Interdemic Selection Model Selfish gene (S) =  repro rate Initial success, ultimate failure A A A S A A A A S S S EXTINCT

9. Problem Group selection cannot counteract individual selection b/c… Rate of allele freq. Δ : ind. selection >>>> group selection Individual generation time is shorter More individuals

10. Patch Model (Maynard-Smith) Alleles: A = altruistic S = selfish S empty A Overuse resources Extinct unless migrate Infected by S Goes to fixation

11. Group Selection Weak force Only if migration is very low & group extinction rates very high Group selection may exist, it just cannot counteract individual selection

12. Traits that benefit other than individual 1.Actually does benefit individual 2.Life history analysis 3.Kin selection

13. Life History Trade-offs Current vs. Future reproduction –“cost of repro” hypothesis Invest now Future Reproduction Future Survival

14. Evidence: future fecundity Collared flycatcher: Gustaffson & Part (1990) Manipulated clutch size, birds with  clutches had  clutches for next 3 years

15. Number vs. Size of Offspring Size often correlates with survival Growth vs. Repro etc… Restraint at time X may benefit ind. at time Y % surviving # offspring / size offspring # offspring N surviving

16. Kin Selection Altruism: incur cost (c) to bestow benefit (b) Contradicts Darwinism: Unlikely NS fix altruistic allele Nepotistic alleles: tend to help sibling Should feed own offspring or sibling? Offspring p(n) = 0.5 (meiosis) Sibling p(n) = 0.5 Allele says either because they are equal

17. Hamilton’s Rule of Inclusive Fitness If : rb > cor r > c/b then help r = degree of relatedness b = benefit (#surviving offspring) c = cost (#lost offspring) e.g. Costs c to help sister (r = 0.5), each gene suffers c but gains b x 0.5 If b/2 >c help b/c  inclusive fitness N.B. r = probability that two individuals have homologous alleles identical by descent

18. Inclusive Fitness Def’n: fitness of gene or genotype in ind. & relatives e.g.: Cousin : b x 0.125 > c As r  b must  or c must  to  fitness “I would give my life for 3 brothers or 9 cousins”

19. Beldings Ground Squirrel Alarm calling: Cost:  predation risk Benefit: ??? Likelihood of calling depends on knowledge of relatedness (philopatry?)…. thus  inclusive fitness

20. Spadefoot Toad Cannibalism Two morphs: omnivore vs. cannibal Cannibals tended not to eat their siblings (Pfennig 1999) Calculated that rb > c European Wood Mouse Sperm Promiscuous females Sperm trains: faster than single sperm Release before reaching egg…many unsuccessful, but improves brothers’ chances