Breeding Structure of...

1) Scrub jays, jackals, mole rats, wild dogs, meerkats

2) Bee-eaters, acorn woodpeckers, groove-billed anis

3) Monkeys, lions, hyenas, elephants

1) Helpers are closely related (usually offspring) and rarely breed

2) Communal breeders with helpers; helpers not always related; >1 female sometimes breeds

3) All females breed and there is little reproductive skew, though some females have higher fitness than others; little direct help; varying degrees of kinship

Monogamous

Females disperse and go with male to his family

Females must decide if staying with parents or leaving the nest will be most beneficial

Indirect fitness benefits of helping must outweigh fitness benefits of dispersing in order for her to stay and help

If stays, she can help with parents nest, or she can also lay a parasitic egg (or not participate)

If she leaves, she can pair off and move with mate to his natal nest, lay a parasitic egg, or not participate in mating season

Females who separated from family at time of pairing make up the largest subset of non-helpers (won't help until own offspring are trying to produce)

90% of redirected help (helping if own mating fails) involves males

Fathers harass the most. Father is so insistent because he is more related to the new kin he might rear with his son's help (0.5) than his son's kin (0.25).

Sons give in to coercion most easily because they are equally related to full sibs or own offspring (0.5) so relatively indifferent. 

1/3 of parasites are unpaired daughters assisting at nest of parents

Direct route (if helpers inherit natal territories from parents)

Indirect rout (if parents w/ helpers rear more offspring than parents w/o non-reproducing assistants)

Hormonal mechanisms underlying helping:

1) In scrub jays

2) In meerkats

1) Prolactin levels.

Prolactin appears to regulate parental care in many birds 

Non-breeding birds in a group exhibit same pattern of increased prolactin production prior to hatching of eggs as do breeding adults

2) In non-breeding male meerkats, an increase in prolactin will cause an increase in baby-sitting. Elevated levels of prolactin may immediately precede babysitting behavior. Cortisol is positively correlated with pup-feeding 

Hormonal mechanisms underlying dominance in wild dogs

Do helpers have lower estrogen/testosterone levels (associated w/ breeding)?

Do helpers have higher cortisol levels (associated w/ stress)?

Fecal estrogens: At baseline, subordinate female has slightly higher levels, but during estrus, while both experience an increase, dominant females far surpass subordinate levels of estrogen

Fecal corticosterone: Alpha females have much higher levels of corticosterone

fGC (fecal glucocorticoid): Alfa female has highest levels, followed by the alpha male (nearly half), closely followed by subordinate female, and then subordinate male

Ecological Constraints related to condition?

Social constraints (when helpers are breeders' offspring)?

Reproductive suppression (when helpers are breeders siblings or unrelated)?

Helpers don't breed due to:

Reproductive suppression (females)

Control by dominant (males)

Inbreeding avoidance (males and females)

Need to exert dominance, higher aggression rates

Higher metabolic costs, activity of breeding

More to lose if litter fails

1) r between recipient of help and the donor

2) degree to which the dominant can manipulate the subordinate ( is group life essential?, can subordinate breed alone?)

3) Does it pay for the dominant to reduce breeding of subordinate?

Reproductive skew is affected by:

Which are ecological constraints?

1) Genetic relatedness (r)

2) Probability that the subordinate can defeat the dominant

3) Expected RS of subordinate breeding alone**

4) Expected breeding productivity of the group if subordinate helps**

(**=ecological constraints)

1) Group members are closely related (white browed scrub wren, lions)

2) Group life is essential

3) Dominant female benefits from help received

Why would females in species with low reproductive skew cooperate?

Defense against predation

Defense of food resources

B may not be much greater than 0

Although females benefit from cooperation, they gain little benefit from direct help, little benefit from suppressing relatives' reproduction (e.g., baboons, mammals, one offspring)

Their own inclusive fitness is enhanced if they both breed AND help relatives to rear young 

*But females may still benefit reproductively from cooperation and close social bonds, especially bonds w/ kin

Female baboons have lower GC levels when...

Higher GC levels when...

In months when her grooming is focused among a few preferred partners (low GC = less stressed)

Lose a close relative (higher GC month after death); she will increase grooming diversity in next 3 months

Strengthen social relationships:

Have lower GC levels when grooming network is more focused and predictable

Compensate for stress associated w/ death of close relative by attempting to identify new grooming partners

Conclusion:

1) As r increases...

2) Why do subordinates tolerate a personal fitness below that of solitary breeder?

3) As the need for group life increases...

4) When individuals are unrelated, dominant can only...

1) so does the bias against subordinates, and the dominant can manipulate more. 

2) RSsub + r (RSdom) > RSsolitary breeder

3) so does the bias against the subordinates, and the dominant can manipulate more

4) reduce the fitness of a subordinate to that of a solitary breeder