Lecture 11 - cooperative breeding Flashcards

1
Q

what is cooperative breeding?

A

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

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2
Q

why is cooperative breeding an evolutionary puzzle?

A
  • think of natural selection favouring individuals that increase their own reproductive success no that of others
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3
Q

describe the diversity of cooperative systems

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

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

A

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

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5
Q

an example of ‘helpers at the nest’ in mammals

A

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

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6
Q

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

A

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
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7
Q

what are plural breeders and an example?

A

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

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

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8
Q

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

A

plural breeders often have a higher degree of conflict

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9
Q

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

A

ecological contraints hypothesis (Elmen 1982)

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10
Q

describe the two step process of the evolution of cooperative breeding

A

step 1) habitat saturation/ecological constraints

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

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11
Q

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

A

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

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12
Q

what is a key assumption of the ecological constraints hypothesis?

A

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

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13
Q

give an example which proves the assumption of the ECH

A

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

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14
Q

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

A
  • 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
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15
Q

what is the issue with correlational evidence

A
  • its not causal evidence - there could be other variables involved
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16
Q

how can you get experimental evidence of cooperative breeding?

A

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

17
Q

example of experimental evidence in the superb fairy-wren

A
  • 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
18
Q

conclusion from superb fairy-wren experiment

A
  • helpers are capable of reproduction
  • habitat is limiting (ecological constraints hypothesis)
  • mates are limiting
19
Q

what is inclusive fitness?

A

direct fitness and indirect fitness

20
Q

what are the direct benefits helpers get from group living?

A

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

21
Q

what is the group augmentation hypothesis?

A

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

22
Q

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

A

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

23
Q

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

A

Cichlid groups more likely to accept immigrants when predation risk high

24
Q

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

A

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

25
Q

give an example of territory inheritance

A

Florida scrub jay

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

26
Q

give an example of increased mate acquisition from group breeding

A
  • 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
27
Q

give an example that proves the skills hypothesis

A

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

28
Q

how does group breeding help direct reproduction?

A

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

29
Q

what are indirect fitness benefits from group breeding

A

1) Increased reproductive success of relatives

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

30
Q

give an example of increased reproductive success of relatives

A

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

31
Q

what is an issue with the long tailed tit study?

A

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

32
Q

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

A

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

33
Q

what is ‘load lightening’?

A

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

34
Q

what data supports the hypothesis of ‘load lightening’

A

difficult to test - only observational data supports the idea