Cooperative Breeding Flashcards
Cooperative Breeding
‘Helpers’ assist breeders to raise offspring that are (usually) not their own
Diversity of cooperative systems
4-9% of bird species
3% of mammal species
described in >10 fish species
‘primitive’ social insects
‘Helpers-at-the-nest’ (80%)
e. g. Florida scrub jay
- pair + 1.8 helpers
- helpers feed and protect young from predators
- helpers usually related to breeding pair
e. g. silver-backed jackal
- pair + 1-3 helpers
- helpers regurgitate food to pups and lactating female
Diversity of cooperative systems
‘Plural breeders’
Several males & females share a nest and raise a communal brood
e. g. Banded Mongoose
- 4-40 in a group
- several females reproduce
e.g. acorn woodpecker
- 2-14 in a group
- often brothers and sisters
typical group
- 1-4 breeding males
- 1-4 breeding females
- up to 8 non-breeding helpers
Evolution of Cooperative Breeding
Ecological Constraints Hypothesis (Emlen 1982)
Habitat saturation / ecological constraints –>
Independent breeding is constrained —>
Grown offspring delay dispersal and “stay at home”
Fitness benefits of helping exceed those of not helping –>
Grown offspring help to rear later broods
EcologicalConstrainstHypothesis Assumption: there is a better fitness return from breeding than helping (but breeding is constrained)
e.g. long-tailed tit
Breeding 0.5 genetic equivalents Helping 0.14 genetic equivalents
ECH Hypothesis: constraints cause offspring to delay dispersal instead of breeding independently
CORRELATIONAL EVIDENCE
‘bad’ years –> more helping e.g. acorn woodpecker
EXPERIMENTAL EVIDENCE
Manipulate constraints effect on incidence on breeding of cooperation?
EXPERIMENTAL EVIDENCE
Manipulate constraints effect on incidence on breeding of cooperation?
e. g. superb fairy-wren
- 60% of pairs have male helpers
- Sex ratio is
1. 8 males : 1 female
Are helpers constrained from breeding?
Exp 1. Male removed from pair
leaving 33 vacancies for 33 helpers —> 31/33 vacancies filled by helpers (within 5hrs)
Exp 2. Male and female removed
leaving 7 empty territories —> 0/7 occupied by helpers
female released (after 3 days) —> 7/7 vacancies filled
Conlusions
- helpers are capable of reproduction
- habitat is limiting (ecological constraints hypothesis) - mates are limiting
Are helpers constrained from breeding?
sociable weaver Covas et al. (2004) FOOD
red-cockaded woodpecker Walters et al. (1992)
NEST CAVITIES
Seychelles warbler
Komdeur (1992)
HIGH QUALITY TERRITORY (FOOD)
superb fairy wren Pruett-Jones & Lewis (1990) TERRITORY + MATE
How do helpers benefit from helping?
Direct fitness: fitness gained from personal reproduction
Indirect fitness: fitness gained from increasing production of
non-descendant kin (via kin selection)
TOGETHER LEAD TO INCLUSIVE FITNESS
Direct Fitness Benefits
(i) Increased survival (benefits of group living)
Group Augmentation Hypothesis
Producing extra offspring benefits helpers by increasing group size
Circumstantial evidence
Kidnapping in banded mongoose and white-winged chough
Experimental evidence
Cichlid groups more likely to accept immigrants when predation risk high
1
Direct Fitness Benefits
(ii) Increased probability of future breeding
Territory inheritance
Florida scrub jay
48% of helpers eventually acquire all or part of parental territory
Mate acquisition Pied kingfisher 1 helpers - close kin 2 helpers - distant kin /non-kin 41% inherited female when breeding male died 18% ousted breeding male
Increased experience (skills hypothesis) SEE TABLE
Direct Fitness Benefits
(iii) Direct reproduction
Seychelles warbler
• Helpers are usually female
• 44% lay eggs in helped nest
• 15% of all young produced by helpers
Indirect Fitness Benefits
(i) Increased reproductive success of relatives
Long-tailed tit, White-fronted bee-eater
Reproductive success increases with no. of helpers
Indirect Fitness Benefits
(ii) Increased survival of related breeders = ‘load-lightening’
Breeder survival increases in larger groups
