Lecture 8 - case study of cooperative breeding in long-tailed tits Flashcards
what was the advantage of the methodical 26 yr study?
any variation that is seen you can put down to evolution and not change in data collection
how were each birds identified?
- Ring each individual - each bird has its own unique colour combination of feathers - easy to identify
what are the tits found in not during breeding season?
-Non-breeding flocks (composed of kin and non-kin) - huddle together and roost at night - to keep warm
what happens to the flocks during breeding season?
the flocks break up and they pair up - no helpers at the start - they try to breed independently
¾ of all nests get destroyed by predators then what happens?
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
how many broods have helpers and how many?
- 50 % of broods have helpers - typically its 1-3 but can be up to 8 helpers
how does helping of long tailed tits differ from usual helping in birds?
- Helping is usually by males and usually a brother of who they are helping - different to the usual pattern of offspring helping parents
do helpers help kin?
pedigrees and genotyping:
77% help close kin, usually a sibling
describe the kin preference experiment carried out on long tailed tits?
- 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
what are the main results from the kin preference experiment?
Results show helpers help kin and the helpers increase productivity (because they are related, they therefore get kin selected advantages)
Do helpers increase breeder survival?
- helpers ‘lighten the load’ of reproduction
- doesn’t affect females but for males when there is a helper they do less work
do the helpers gain any direct fitness benefits?
- Doesn’t help current reproduction - no parentage of the brood they care for - no EPC
do the helpers gain any future benefits?
no - results showed helpers in year x have the same probability of future survival and reproduction as non-helpers
what are the 2 potential costs of helping?
1) opportunity cost - opportunity of breeding is lost while helping others
2) survival cost
what were the costs to the long tailed tits for helping?
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
what are the two potential benefits of helping?
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
for the long tailed tits what are the processes generating kin structure?
-Nearby males are more likely to be related to you
kin selection can only operate if there are frequent interactions among kin, what are the 3 drivers behind kin structure?
1) Limited dispersal
2) Coordinated dispersal of kin
3) Small effective population size - different life histories
describe how limited dispersal affects kin structure of long tailed tits
- local recruitment of both sexes
- natal dispersal is female-biased
- means kin are available to help each other in future years
describe how coordinated dispersal of kin affects kin structure of long tailed tits?
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
describe how life history traits affect kin structure of long tailed tits?
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
what are 3 factors predicted to be important in long tailed tits that contribute to helping behaviour?
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.
the 3 cooperation factors: nest predation, length of breeding season and relatedness can be applied to the ecological constraints hypothesis what does this demonstrate?
- Demonstrates how constraints often very specific to systems
what did comparison studies of the long tailed tits show about the predicted 3 factors?
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
