L12 Flashcards
Examples of species that co-operatively breed:
-Meerkats
- Social insects
What is co-operative breeding characterized by?
- The presence of helpers
- Eg cleaning, mutualistic feeding
- Individuals who help hamper their own reproductive success
Diversity of cooperative systems
- Cooperative breeding has different interpretations
- Most widespread in birds 4-9% of bird species
- 3% of mammal species
- Described in >10 fish species
- Social insects that aren’t yet eusocial
In what species is cooperative breeding most widespread?
Birds
Helpers at the nest e.g. Florida Scrub Jay
- Florida scrub Jay
- Pair + 1.8 helpers
- Helpers feed and protect young from predators
- Helpers usually related to breeding pair
Helpers at the nest eg Silver backed Jackal
- Pair + 1-3 helpers
- Helpers regurgitate food to pups and lactating female
Helpers at the nest eg Naked mole rat
- Naked mole rat
- Larger societies up to 80 individuals
- Queen breeds
- Normal moles have different morphology to queen
- Reproductive division of labour (some fight, some forage, reproductive female breeds in chamber)
- Dispersal morphs who try and founder new colonies
- Debated whether it is a caste system or part of species aging
Plural breeders
Several males and females share a nest and raise a communal brood
Banded mongoose
-Plural breeders
- 4-40 individuals in a group - Several reproductive females and males
Acorn woodpecker
- Plural breeding
- 2-14 individuals in a group
- Reproductive individuals are often brothers and sisters
- These breed with individuals that have moved into the colony
- Helpers are non-breeding
Ecological constraints hypothesis
Independent breeding is constrained - thus leading to grown offspring delay dispersal and stay at home
1. Habitat saturation/ ecological constraints
Grown offspring delay dispersal and stay at home leads to grown offspring helping to rear later broods
- Fitness benefits of helping exceed those of not helping
Main assumption of the evolutionary constraints hypothesis
there is a better fitness return from breeding than helping (but breeding is constrained)
Species Example eg Long-tailed tit
Genetic equivalents = fitness
Breeding productivity = 0.5 GE
Helping = 0.14 GE
Hypothesis: constraints cause offspring to delay dispersal instead of breeding independently
Correlational evidence
- Bad years = more helping - Good years = less helping
Acorn woodpecker
- In nearly all bad years (low acorn crop) there is high delayed dispersal
- In good years (high acorn crop) there is less delayed dispersal
> 2Y acorn woodpeckers
- Less delayed dispersal
Superb fairy wren
- 60% of pairs have male helpers
- Arise due to male sex ratio
- Sex ratio at birth is 1:1 but many females die so it is 1.8M: 1F
Are fairy wren helpers constrained from breeding experiment 1?
Male removed from pair
Leaving 33 vacancies for 33 helpers
31/33 vacancies filled by helpers (within 5 hours)
Are fairy wren helpers constrained from breeding experiment 2?
- Removed male and female
- Empty territories
- Initially helpers didn’t take over territory as there was no reason (no one to mate with)
- Female released (after 3 days) then 7/7 vacancies filled
- No interest in helping, strictly reproducing
Are fairy wren helpers constrained from breeding conclusions
- Helpers are capable of reproduction
- Habitat is limiting (ECH)
- mates are limiting
- Habitat is limiting (ECH)
Experimental work has revealed different constraints such as…?
- Food
- Nest cavities
- Territory and mate
- High quality territory (food)
How do helpers benefit from helping?
Direct fitness: fitness gained from personal reproduction
and
Indirect fitness: fitness gained from increasing production of non-descendant kin ( via kin selection)
The three direct fitness benefits:
- Increased survival
- Increased probability of future breeding
- Direct reproduction
Group augmentation hypothesis
Benefits may select for helpers to then keep adding to benefits
Increased survival
- Group augmentation hypothesis
Producing extra offspring benefits helpers by increasing group size
Kidnapping in banded mongoose and white-winged chough
Gaining benefits associated with larger group living
- Some cons of group living but benefits must outweigh for it to occur
Experimental evidence for increased survival
- Cichlid groups more likely to accept immigrants when predation risk is high
Increased probability of future breeding
Territory inheritance
48% of helpers eventually acquire all or part of parental territory so they can become breeders
Mate acquisition
- Pied kingfishers
Primary helpers
- Relatives
Secondary helpers
- Not relatives - Don’t benefit indirectly but buy their way into a territory and inherit female when the male dies
Kick out breeding male sometimes
Increased experience (skills hypothesis)
- Comparison of success of various breeders eg 1st time, previous breeders
- 1st time breeders who never helped had no/ low reproductive success
- 1st time breeders who helped had more reproductive success as did previous breeders
Direct reproduction
- 44% lay eggs in helped nest
- 15% of all young produced by ‘helpers’
- Helpers are usually female
- Helpers taking advantage of producing their own offspring
- Not strictly helpers
Indirect fitness benefits
- Increased reproductive success of relatives
- Increased survival of related breeders
Increased reproductive success of relatives
- Long-tailed tit
- Reproductive success increases with no of helpers
- Raised by offspring alone reduces survival chance
- If helpers Is related there is a large indirect payoff
White fronted bee-eater
- Reproductive success increases with no of helpers - However these correlation studies may be a result of more individuals in group size, more experienced parents etc
Does removal of helpers impact reproductive success?
Removal experiments
- Socially disruptive - No sig effect on all species, but some species there is an effect
Increased survival of related breeders
= load-lightening
- Investing more in reproduction means less in self- maintenance - Helpers can assist with costs
Hatchwell 1999
- 20/26 species of cooperative breeder - One or both parents reduce their effort when assisted by helpers - improved parental survival hard to demonstrate
Helpers are typically related to breeders
