Lecture 8 - case study of cooperative breeding in long-tailed tits

Question 1

what was the advantage of the methodical 26 yr study?

Answer 1

any variation that is seen you can put down to evolution and not change in data collection

Question 2

how were each birds identified?

Answer 2

• Ring each individual - each bird has its own unique colour combination of feathers - easy to identify

Question 3

what are the tits found in not during breeding season?

Answer 3

-Non-breeding flocks (composed of kin and non-kin) - huddle together and roost at night - to keep warm

Question 4

what happens to the flocks during breeding season?

Answer 4

the flocks break up and they pair up - no helpers at the start - they try to breed independently

Question 5

¾ of all nests get destroyed by predators then what happens?

Answer 5

if the nest fails early in the season the pair will have another go but if its late, they will abandon and a proportion of them will become helpers - Decision to breed again or help depends on date

Question 6

how many broods have helpers and how many?

Answer 6

• 50 % of broods have helpers - typically its 1-3 but can be up to 8 helpers

Question 7

how does helping of long tailed tits differ from usual helping in birds?

Answer 7

• Helping is usually by males and usually a brother of who they are helping - different to the usual pattern of offspring helping parents

Question 8

do helpers help kin?

Answer 8

pedigrees and genotyping:

77% help close kin, usually a sibling

Question 9

describe the kin preference experiment carried out on long tailed tits?

Answer 9

• Manipulated breeding success to offer potential helpers’ choices of who to help
• Nests were equally distant from the failed nest
• In 16 or 17 cases they chose to go and help the relative = active kin discrimination
• Another experiment showed that they also make a second decision on how hard they work depending on level of relatedness - just as Hamilton’s rule predicts

Question 10

what are the main results from the kin preference experiment?

Answer 10

Results show helpers help kin and the helpers increase productivity (because they are related, they therefore get kin selected advantages)

Question 11

Do helpers increase breeder survival?

Answer 11

• helpers ‘lighten the load’ of reproduction

- doesn’t affect females but for males when there is a helper they do less work

Question 12

do the helpers gain any direct fitness benefits?

Answer 12

• Doesn’t help current reproduction - no parentage of the brood they care for - no EPC

Question 13

do the helpers gain any future benefits?

Answer 13

no - results showed helpers in year x have the same probability of future survival and reproduction as non-helpers

Question 14

what are the 2 potential costs of helping?

Answer 14

1) opportunity cost - opportunity of breeding is lost while helping others
2) survival cost

Question 15

what were the costs to the long tailed tits for helping?

Answer 15

1) opportunity of breeding is lost while helping others - found this to not be the case for long tailed tits
2) Survival cost?
Helper survival = 56%
Non-helper survival = 79%
Can convert this to direct fitness benefits
effect of helping on survival = -23%
effect of helping on direct fitness = -0.029 adult recruits

Helping therefore must be altruistic because there is a cost to the helper

Question 16

what are the two potential benefits of helping?

Answer 16

1) Productivity - Marginal effect of one helper…+0.29 adult recruits
2) Load- lightening - Marginal effect of one helper on male survival translates to…+0.01 adult recruits

Question 17

for the long tailed tits what are the processes generating kin structure?

Answer 17

-Nearby males are more likely to be related to you

Question 18

kin selection can only operate if there are frequent interactions among kin, what are the 3 drivers behind kin structure?

Answer 18

1) Limited dispersal
2) Coordinated dispersal of kin
3) Small effective population size - different life histories

Question 19

describe how limited dispersal affects kin structure of long tailed tits

Answer 19

• local recruitment of both sexes
• natal dispersal is female-biased
• means kin are available to help each other in future years

Question 20

describe how coordinated dispersal of kin affects kin structure of long tailed tits?

Answer 20

when long-tailed tits disperse, they often do so with relatives, so dispersal does not necessarily result in birds moving away from their relatives, so kin interactions can occur post-dispersal

Question 21

describe how life history traits affect kin structure of long tailed tits?

Answer 21

The very high rate of nest predation means that a relatively small number of pairs reproduce successfully, but each brood produces a lot of related fledglings from which a large proportion of next year’s recruits are drawn. Thus, there is a small effective population size. This contrasts with more typical avian life histories (e.g. great tits) where many pairs are successful, producing many fledglings, of which relatively few survive to become breeders; i.e. there is a large effective population size. This simple difference in the timing of offspring mortality has a profound effect on the emergent population kin structure

Question 22

what are 3 factors predicted to be important in long tailed tits that contribute to helping behaviour?

Answer 22

1) nest predation rate - The very high rate of nest predation means that a relatively small number of pairs reproduce successfully, but each brood produces a lot of related fledglings from which a large proportion of next year’s recruits are drawn. Thus, there is a small effective population size. This contrasts with more typical avian life histories (e.g. great tits) where many pairs are successful, producing many fledglings, of which relatively few survive to become breeders; i.e. there is a large effective population size. This simple difference in the timing of offspring mortality has a profound effect on the emergent population kin structure
2) length of the breeding season - In a short season there will be little time to have multiple attempts to raise your own brood, whereas in a long season each pair can have multiple attempts. Therefore, helping was predicted to be negatively correlated with the length of the breeding season.
3) relatedness -If the presence of kin is necessary for failed breeders to become helpers, then helping was predicted to increase as average population relatedness increased.

Question 23

the 3 cooperation factors: nest predation, length of breeding season and relatedness can be applied to the ecological constraints hypothesis what does this demonstrate?

Answer 23

• Demonstrates how constraints often very specific to systems

Question 24

what did comparison studies of the long tailed tits show about the predicted 3 factors?

Answer 24

the prevalence of helping in the population peaked at intermediate levels of nest predation, with low prevalence at low and high rates of predation. Secondly, the intensity of helping decreased as the length of breeding seasons increased, again as predicted. In contrast, there was no significant relationship between helping and relatedness, probably because it is the kinship of individuals that matter rather than relatedness at the level of the population