Mating Systems Continued

Female choice polygyny in redwinged blackbirds

14 pairs of males and their territories Male #1: has one mate Male # 2: has no mate Nest platform over water (very good) Nest platform over land (bad) ? It may pay a female to be in a polygynous relationship with a high quality male over a monogamous relationship with a low quality male. How do you make the decision? Think of a bus filling up…front seats go first, then people start pairing up before all the back seats start filling. If you’re a female, where do you go?

14 pairs of males and their territories Male with one mate Male with no mate Nest platform over water (good) Nest platform over land (bad) 12 got a new female first 2 got a new female first It may pay a female to be in a polygynous relationship with a high quality male over a monogamous relationship with a low quality male. How do you make the decision? Think of a bus filling up…front seats go first, then people start pairing up before all the back seats start filling. What are the tradeoffs involved from the standpoint of the female? How should females behave towards other females? Are there tradeoffs for the male?

Polygyny threshold model monog polyg Biological fitness Threshold: After red line fitness decreases rapidly with territory quality. Better to join another female on a high quality territory than to settle mono- gamously with a male on a bad territory. Territory quality

What are females choosing, especially when they are making the best of a bad situation? Good parenting skills—probably the best/ideal situation (Parental investment) Good resources—Probably the next best situation, potentially part of parental investment Good genes and/or good looks—epigamic selection (selection for gametes) Greater resistance to diseases Production of sexy sons and sexy grandsons How do you choose good genes? Think about mechanisms; smell? (prob. not in birds), extravagant signals—especially honest signals.

How does lekking (lek polygyny) evolve? Typical Manacus lek

No resources to defend (fruit is patchy in space and time) Need a central place in which to locate mates—where females are likely to pass, or where females know where to find males Females practice epigamic selection, and can directly compare all males together… Did it start as runaway selection on a beneficial trait? Is dancing ability an honest signal of quality? But what do males get out of this? Especially if most males are losers?

What do males get out of this? Occasional chances to mate Practice doing the dance? Opportunity to take over from the top male? Alternative mating strategies? Indirect Fitness benefits Shorey et al. 2001

Kin Selection: selection of a trait through helping relatives Through descendant kin (offspring): direct selection - or - Through non-descendant relatives: indirect selection inclusive fitness = direct + indirect nepotism = helping relatives other than offspring

Evolution of Cooperative Breeding (reproductive altruism) Why help? Kin selection? Yes, but it’s often not the whole story Learning how to parent? Chance of getting a territory? Some individuals are making the best of a bad situation

White-fronted Bee-eaters --Monogamous --3-17 member families --Siblings, cousins, nephews, grandparents, etc. --Unpredictable environment --Long-term memory of helpers --Dominant male will share his mate if he needs extra help --Young females look for dominant male to pair with or parasitize their mother at same time mom is laying.

Do helpers actually help? YES. There is a cost to the helper and benefit to receiver Only 43% of ‘solo pair’ nesting attempts produce 1 fledgling. # Fledgies = 0.44 X (# Helpers + 1)

Reproductive altruism and the case of the Florida Scrub Jay 1 breeding pair Up to 6 helpers Helpers are helpful! Increase feeding and ward off predators. If you can produce more genetic units on your own, why not go off on your own then? Territory availability may be limiting. Learn good parenting skills first?

What is the fate of helpers? Male vs. female helpers? Females immediately disperse and replace female openings on other territories (females prefer not to help) Males hang out on natal territory with oldest/dominant son getting priority when father dies Should upstart males take over earlier? Or leave? Depends on how strong Dad is and availability of territories Annexing other territories? Florida Scrub Jay families will expand their territories annexing space for big brother. Should parents accept non-relatives? When desperate yes (although relatives should be better helpers). Otherwise no. Don’t want to potentially have a non-relative usurp you or cuckold you. Who do you recruit as your helper if you have no offspring yet? Green Wood Hoopoe males recruit younger offspring (who benefitted from their help early in life) Kidnapping in White Winged Choughs—provide a good safe haven for the juvenile and then get them to stay on as helper.

Experimental study of reproductive altruism: Manipulate territory availability Easy to do with cavity nesting species, or transplant birds to vacant habitats (Seychelle’s warbler transplanted to vacant habitat on other islands) In some species shows that helpers are not only capable of breeding, but would rather breed on their own if resources available. In others (White Winged Choughs) males incapable of breeding without first learning skills from parents through helping. Interesting anecdote in choughs: Solitary breeding not possible, and in some cases need to recruit (kidnap) unsuspecting young from other families to help out. Recruiting can be done with food enticement and some young choughs accept. Remove helpers from nests Parents fledge fewer young—so helpers are actually being useful, not just hanging out or distracting parents. Manipulate quality of helping behavior In Tree Swallows, parents retaliate against helpers if they find their offspring dead or removed from cavity.

Why help? Indirect fitness benefits - raise siblings - enhance survival of parents (help parents produce more siblings) ‘Indirect’ direct fitness benefits - helping as training - inherit territory (males) Ecological constraints - habitat saturation (chance of getting territory poor) - limited food resources - predation pressure Reciprocal benefits? Rare in birds Promiscuous mating systems—Superb Fairy Wren Can’t figure out who’s who, although prefer to help kin when they can

Is Kin Selection Dead? E.O. Wilson says it is What do you think? What explains why reproductive altruism occurs in the previous examples? Can reproductive altruism occur without kin selection? Is it more likely to occur if kin selection is part of the puzzle?

Hamilton’s Rule Altruism can occur when: Br – C > 0, or stated another way: Br > C Where B = benefit to recipient C = cost to altruist r = relatedness of altruist to recipient of altruism

An Example of Kin Selection: American Turkeys Related males frequently form dominant/subordinate pairs to attract females, but only the dominant mates. This is a lek-like system. How would subordinate behavior evolve?

1. help dominant produce 20 chicks, or 2 strategies: 1. help dominant produce 20 chicks, or 2. be selfish, and brother produces 8, you produce 4. What should you do? By helping your brother, he produces: 20 – 8 = 12 offspring more than usual—this is his benefit, and your indirect fitness. By being selfish, your direct fitness is: 4—this is also your cost when you sacrifice your own reproduction to help. Your relatedness to your brother: ½, on average. So, if B = 12, r = ½ and C = 4, then 12(1/2) > 4 IT PAYS TO BE A SUBORDINATE HELPER!

All else being equal, those who help will leave more genetic units to the next generation, so the behavior should increase in frequency over time.