1. Sexual Selection NS: who SURVIVES SS: who REPRODUCES SS can explain some deleterious/costly characteristics that can’t be explained by NS Ornaments/Courtship Displays/Fights Sexual Dimorphism differences among indivs in mating opportunity

2. Types of Sexual Selection Competition (usually M) Sperm is cheap  RS with # of matings Choice (usually F) Eggs are expensive No Δ in RS with # of matings # offspring # mates  e.g. Newts

3. Sexual Selection depends on Investment Higher investment = limited resource  Usually Indiscriminate M & Choosy F But, Sex role reversal/ biparental care/nuptial gifts

4. Male-male competition 1) COMBAT Competition for access to F or territory Correlation b/w dominance rank & # of matings Size often important in competition (Sexual Size Dimorphism ~ Degree of Polygyny) e.g. 2: Male marine iguanas larger than optimal for survival e.g. 1: Elephant Seals

5. 2) Sperm competition Fertilization more important than mating 1) Large ejaculate/lots of sperm 2) Mate guarding 3) Copulatory plugs 4) Sperm removal Comparative method: relative testis size often correlates to mating system e.g. Primates 200 kg: 30 g 45 kg: 110g70 kg:40g

6. 3) Infanticide Males increase repro opportunities Not good for female Often female has no choice e.g. Lions

7. Female Choice – Benefits? On Basis of Resources vs. In Absence of Resources e.g. Scorpionflies “making males pay” Nuptial gift: arthropod – salivary – forced copulation

8. Polygyny Threshold e.g. Lark Bunting choose on the basis of M territory Fitness benefits male territory quality ranked according to shade day of female arrival

9. Direct Benefit F may choose on the basis of : gift, paternal care, territory If no M investment, how do F choose?

10. Non-resource based Female Choice Mutant F with no preference for showy M non-showy M offspring survive better M offspring not preferred as mates survival benefit must > repro benefit

11. Runaway Sexual Selection Innate female preference for showy M

12. The ‘Runaway’ Process SS trait associated with higher survival Mutant F (preference) =  RS b/c high quality sons 2  advantage: M with trait preferred by high proportion of pop’n as mutation spreads Reinforcement Offspring carry genes for trait & preference (linkage disequilibrium) Advantage: Survival  Survival + Mating  Mating

13. Honest Advertisement F preference for traits which demonstrate good quality Zahavi – Handicap Principle –Characters that reduce survival –“I must be good to pull this off” (good genes) –Indicator must be costly so M can’t cheat –Often cost of trait is less for high quality males

14. Runaway vs. Good Genes Open-ended Heritable variation in male character SS b/c sons have mating advantage Open-ended Heritable variation in male fitness SS b/c sons have survival advantage

15. Indicators of Health e.g. guppies – orange: diet quality Special case of “good genes”: –Hamilton & Zuk : parasite load & plumage brightness –Species (not individuals) with brighter plumage gen’lly higher parasite load  able to use colour as indicator of risk of parasitism