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Behavioural Ecology
Cooperative breeding
| Question | Answer |
|---|---|
| The evolutionary paradox of cooperative breeding | • Individuals help other individuals to reproduce, at a cost to themselves • Altruistic behaviour ? • Contradicts the idea that individuals should maximise their own reproductive success! |
| Vertebrate cooperative breeding systems | Situation where adult individuals, in addition to the genetic parents, stay within a group and regularly aid in the rearing of young |
| Diversity of cooperative breeding systems | Helpers at the nest (80% of CBS): Breeding pair + one or more subordinate individuals that contribute to feeding and/or protecting pair’s offspring Plural breeding: Several males and females share a nest and raise a communal brood |
| Altruistic behaviour | • Do individuals really help other individuals to reproduce? • Is this at a cost to themselves? |
| Do helpers really benefit dominants? | They could help by: • Increasing the reproductive success of the breeders • Increase breeder survival |
| Is there a cost to helping? | Individuals that helped most had worse body condition at the end of the season and lower future survival |
| Is there a cost to helping? | In Meerkats helping is condition dependent – Only help when above threshold weight – Short term cost – lose weight – Stop helping when drop below threshold – No reduction in survival Behavioural modification – reduce long term costs |
| Why do cooperative breeding systems evolve? | Kin selection An individual can increase the number of copies of its genes in future generations by helping to increase the reproductive success of close relatives (W.D Hamilton 1964) |
| Hamilton's rule | A costly action should be performed if: C < B x R C = cost in fitness to the actor, B = fitness benefit to the recipient R = genetic relatedness between the actor and the recipient |
| Why do cooperative breeding systems evolve? | Eusocial insects/microrganisms - consistently high levels of relatedness between sibs - kin selected benefits do seem to explain altruistic behaviour |
| Why do vertebrate cooperative breeding systems evolve? 1) Group living Ecological constraints | • individuals join a group (or don’t leave their natal territory) because there are no good breeding opportunities available |
| Why do vertebrate cooperative breeding systems evolve? 2) Benefits of philopatry (staying in a group) | • Increased survival • Increased chance to inherit territory • Ability to safely look for breeding opportunites |
| But does group living automatically lead to cooperative breeding? | Why do individuals help? |
| Benefits of helping Indirect (kin selected) benefits | • In many systems, young individuals delay dispersal and help parents raise subsequent offspring • So kin selection has been the favoured explanation |
| Direct benefits - increase an individuals own lifetime reproductive success | – Pay to stay – Acquisition of a mate – Group augmentation ? – Gain breeding experience – Direct breeding |
| Relative roles in cooperative breeding | Direct present - increased survival Direct future - increased prob of breeding/reproductive success as a breeder |
| Relative roles in cooperative breeding Overall benefits of staying & helping > benefits gained by leaving! | Indirect present - increased production of non-descendent kin Indirect future - increased survival/production of kin/survival |
| Cooperative breeding in the seychelles warbler | Constraints • Limited breeding territories available • When translocated – independent breeding – until the new island was saturated |
| Cousin Island 1997- | > 96% of birds individually colour ringed and blood sampled • All territories mapped and monitored • Breeding attempts followed |
| Cousin Island 1997- | • Status of adults in cooperatively breeding territories (30%) was determined • All chicks blood sampled (1 or 2 chicks/nest) |
| Parentage and relatedness | • 30 microsatellite loci used for genotyping • Parentage – Assigned using CERVUS; Marshall 1998 • Relatedness – Based on genotype similarity |
| Direct kin versus indirect kin benefits | • High direct benefits • Low indirect benefits • Females gain more benefit than males |
| Conclusions for the SW | 1. high levels of subordinate breeding and extra-group paternity 2. Reduced subordinate-nestling relatedness 3. More direct than indirect benefits to cooperative breeding |
| Conclusions for cooperative breeding | 1. Direct benefits can be the main benefits gained by subordinates 2. both direct and indirect benefits may be important Does this mean that direct benefits have caused the evolution of cooperative breeding? |
Created by:
rose.coo
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