Lecture 11 - cooperative breeding

Question 1

what is cooperative breeding?

Answer 1

‘Helpers’ assist breeders to raise offspring that are (usually) not their own

Question 2

why is cooperative breeding an evolutionary puzzle?

Answer 2

• think of natural selection favouring individuals that increase their own reproductive success no that of others

Question 3

describe the diversity of cooperative systems

Answer 3

• 4-9%of bird species
• 3% of mammal species
• describe in >10 fish species
• primitive social insects

Question 4

80% of cooperative systems involved ‘helpers at the nest’ give an example of this in birds

Answer 4

e. g. Florida scrub jay
- pair + 1.8 helpers
- helpers feed and protect young from predators
- helpers usually related to breeding pair

Question 5

an example of ‘helpers at the nest’ in mammals

Answer 5

e. g. silver-backed jackal
- pair + 1-3 helpers
- helpers regurgitate food to pups and lactating female

Question 6

give an example of a mammal with an extreme cooperative system similar to that of eusocial insects

Answer 6

naket mole rats - high defree of sophistication in social system

• reproductive division of labour: queen,soldiers,foragers
• can live in colonies of 80-100 individuals

Question 7

what are plural breeders and an example?

Answer 7

Several males & females share a nest and raise a communal brood

e. g. Banded Mongoose
- 4-40 in a group
- several females reproduce

Question 8

what is the difference between plural breeders and ‘helpers at the nest’

Answer 8

plural breeders often have a higher degree of conflict

Question 9

what overarching theory explains the diversity of social systems and phenomenon in generality

Answer 9

ecological contraints hypothesis (Elmen 1982)

Question 10

describe the two step process of the evolution of cooperative breeding

Answer 10

step 1) habitat saturation/ecological constraints

step 2) fitness benefits of helping exceed those of not helping

Question 11

where do the two steps fit in on an evolutionary timeline?

Answer 11

independent breeding is constrained
(1)
grown offspring delay dispersal and ‘stay at home’
(2)
grown offspring help to rear later broods

Question 12

what is a key assumption of the ecological constraints hypothesis?

Answer 12

there is a better fitness return from breeding than helping (otherwise you have no need for constraints) but breeding is constrained

Question 13

give an example which proves the assumption of the ECH

Answer 13

e. g. long tailed tits
- as a breeder an individual gets 0.5 genetic equivalents whereas the pay off from helping is just 0.14
- proves that breeding is better than helping which pushes towards the conclusion that helping must be constrained in some way

Question 14

describe correlations evidence that supports the hypothesis that constraints cause offspring to delay dispersal
instead of breeding independently

Answer 14

• look over a number of years and see what the ecological conditions were like to see if helping varies over ‘bad’ years
  e. g. acorn woodpecker stores acorns - the larger the acorn crop the less constraint on independent breeding - in years with good acorn crop there is evidence of fewer individuals delaying dispersal

Question 15

what is the issue with correlational evidence

Answer 15

• its not causal evidence - there could be other variables involved

Question 16

how can you get experimental evidence of cooperative breeding?

Answer 16

researchers manipulate constraints on breeding and see if there was an effect on incidence of cooperation

Question 17

example of experimental evidence in the superb fairy-wren

Answer 17

• 60% of pairs have helpers
• always male
• strong male bias sex ratio 1.8 male:1 female
• they removed males away from territories leaving the female without a partner and open vacancies for helpers
• the vacancies were rapidly filled by helpers showing that helpers are capable of reproduction but they dont often have the opportunity
• exp 2 - male and female removed - none of the territories were filled suggesting the helpers must be gaining from staying where they are and helping

Question 18

conclusion from superb fairy-wren experiment

Answer 18

• helpers are capable of reproduction
• habitat is limiting (ecological constraints hypothesis)
• mates are limiting

Question 19

what is inclusive fitness?

Answer 19

direct fitness and indirect fitness

Question 20

what are the direct benefits helpers get from group living?

Answer 20

1) increased survival -group augmentation hypothesis (Producing extra offspring benefits helpers by increasing group size)
2) increased probability of future breeding
3) direct reproduction

Question 21

what is the group augmentation hypothesis?

Answer 21

better to live in a large group - therefore have to help with rearing the offspring

Question 22

circumstantial evidence of increased survival being a benefit a group living?

Answer 22

Kidnapping in banded mongoose and white-winged chough - want to expand their group size at any expense even by raising non-kin

Question 23

experimental evidence of increased survival being a benefit a group living?

Answer 23

Cichlid groups more likely to accept immigrants when predation risk high

Question 24

what are 3 ways group living will increase the probability of future breeding?

Answer 24

1) territory inheritance
2) mate acquisition
3) increased experience (skills hypothesis)

Question 25

give an example of territory inheritance

Answer 25

Florida scrub jay

48% of helpers eventually acquire all or part of parental territory

Question 26

give an example of increased mate acquisition from group breeding

Answer 26

• pied kingfishers have 2 kinds of helpers 1) close kin of breeding pair 2) distant kin/non-kin
• when secondary helpers try to settle the breeding male is initially very resistant but they eventually settle
• in 41% of cases the secondary helper ‘inherited’ female when breeding male died
• in 18% they ousted breeding male

Question 27

give an example that proves the skills hypothesis

Answer 27

Seychelles warbler - Comparison of success of 4yr old birds
- results showed that previous experience made you a successful parent in terms of hatching success and number of fledglings

Question 28

how does group breeding help direct reproduction?

Answer 28

e.g. seychelles warbler - Helpers are usually female
44% lay eggs in helped nest
15% of all young produced by ‘helpers’
- females typically seek copulation on other territories to avoid inbreeding

Question 29

what are indirect fitness benefits from group breeding

Answer 29

1) Increased reproductive success of relatives

2) Increased survival of related breeders= ‘load-lightening’

Question 30

give an example of increased reproductive success of relatives

Answer 30

long tailed tit - Reproductive success increases with no. of helpers i.e. the offspring had a better chance at survival with more food etc

Question 31

what is an issue with the long tailed tit study?

Answer 31

just correlational evidence not causation - have to manipulate an experiment to prove it

Question 32

give an example of an experiment proving the indirect fitness benefit of increased reproductive success of relatives

Answer 32

experiment using moorhens, grey-crowned babbler and florida scrub jays
- did a control and removal of helpers - results showed significant reduction in reproductive success

Question 33

what is ‘load lightening’?

Answer 33

if the presence of helpers means breeders have to do less it will result in the increased survival of breeders

Question 34

what data supports the hypothesis of ‘load lightening’

Answer 34

difficult to test - only observational data supports the idea