Reciprocal altruism in bats Flashcards
Who conducted the initial studies on the common vampire bat?
Wilkinson, 1984
What is the latin name for the common vampire bat?
Desmodus rotundus
What did Wilkinson (1984) find?
That bats regurgitate blood meals to save roost mates from starvation
In what three ways could you describe the regurgitation behaviour of bats?
- Group selection
- Kin selection
- Reciprocal altruism
Where were the experiments on D. rotundus carried out? For how long?
Northwest Costa Rica for 26 months
Which sex is philopatric in D. rotundus?
Females
Do females move between roosting sites?
Yes
Do males associate with females?
No
How many roosting sites were involved in the study?
14
What was the population of D. rotundus estimated at? How many individuals were ID tagged?
Estimated at 200, 184 were tagged
How was relatedness assessed?
Direct observation of mothers nursing their offspring
When was regurgitation observed?
When roost mates had failed to obtain a blood meal for themselves
How did capture experiments confirm the cause of sharing?
In a captive group an individual was prevented from feeding. Upon release roost mates shared their blood meals with her.
The experiments were repeated after feeding; upon release no blood meals were shared.
In which age category was failure to obtain a blood meal more common? Why?
Younger bats, presumably due to hunting inexperience
What is group selection?
Where group selection acts on a group as a whole, rather than on individuals.
What does group selection require?
Cooperation of all individuals within the group to behave ‘for the good of the group’.
Group selection favours populations of…
altruists
How many cases of blood meal sharing were observed in the experiment?
How many occurred between mother and offspring?
How many occurred between unrelated individuals that displayed close association?
110
77
21
How can group selection be used to explain blood meal sharing?
Bats shared with unrelated individuals as it increased survivorship of the entire group as less members die of starvation
What disproves group selection as the reason for blood meal sharing in bats?
Males are consistently excluded from sharing, both in the wild and in captivity (proven by Wilkinson’s captive experiment with one male in an all-female group)
Why are males excluded from sharing?
As they are the dispersing sex and do not co-roost with females for prolonged periods of time, so there is no guaranteed future pay-off to the donor in sharing with a male
ALTRUISM DOES NOT PERSIST WITHOUT BENEFIT TO THE INDIVIDUAL
Why is group selection a contentious theory? Give 2 reasons.
- Natural selection relies on random mutations with unforeseen effects in response to environmental changes. Under group selection groups systematically change their strategy.
- Group selection assumes individual selection is not acting on group members, when in reality each member wishes to proliferate their genes. This is why cheaters invade and can spread to fixation.
What is kin selection?
The preference for relatives due to inclusive fitness (shared genes by descent)
How can kin selection be used to explain regurgitation in bats? Refer to Hamilton’s rule.
77 cases between related individuals were observed. Relatedness between mother and offspring = 0.5, thus it is possible that rb > c
Why is kin selection not responsible for regurgitation in bats? Refer to Hamilton’s rule.
21 cases were observed between non-related individuals, where r = 0. Thus it is likely that rb
Why would a mother want to save her starving offspring?
So the offspring can go onto proliferate the mother’s genes, is actually a selfish act
Why might 77 cases of mother-offspring regurgitation have been observed, NOT because of relatedness?
Because of close association and proximity; mothers and daughters roost next to each other
If mothers roost next to younger daughters and adults, both of which they are affiliated with, why might it be more common to observe regurgitation between mother and daughter?
Because younger bats are inexperienced at hunting and more likely to need rescuing than adult roost mates
What is reciprocal altruism?
When an individual commits a selfless act with the expectation of future payback
What is reciprocal altruism based on?
Repeated interaction
What are the three conditions required for reciprocal altruism?
- Repeated, pair-wise interaction
- Benefit must exceed cost
- Non-reciprocators can be identified and avoided
How do we know bats have repeated pair-wise interactions, indicating reciprocal altruism?
They roost with the same individuals for years and can live up to 18 years old, presenting lots of opportunities for reciprocity
How do we know benefits exceed costs, indicating reciprocal altruism?
After a blood meal bat weight declines exponentially due to a high metabolism and evaporative water loss. Therefore time to death is rapid. A bat that donates blood will lose less time than the recipient will gain.
How do we know non-reciprocators are identified and not shared with, indicating reciprocal altruism?
Males are not shared with as they do not reciprocate blood meals
How can males be distinguished from females?
They are smaller, presumably also olfactory and sonic differences
How could we prove regurgitation is attributed to reciprocal altruism with further tests? What two things would need to be tested?
That conditions for reciprocal altruism are always filled:
- That repeated pair-wise interaction leads to RA
- That non-reciprocators are identified
How would we test for repeated pairwise interactions that lead to RA?
- Wild behavioural focals
- Observe a new arrival at a roosting site that is not affiliated with the existing females, see how they behave towards her (wild and captive experiments)
- Captive studies between unrelated and related groups that are then mixed
Explain how captive studies between unrelated and related groups that are then mixed would indicate RA.
What would we assume under RA?
(CONTROL) Two groups, all individuals unrelated, leave to establish close bonds, then mix. See whether individuals that already know each other associate more.
Two groups, related bats initially kept in separate groups, upon mixing see whether they share with relatives they haven’t associated with or with non-relatives they have roosted with previously.
Under RA, assume that bats associate with previous roost mates, not distant relatives
Males are easily identified as non-reciprocators due to sexual dimorphism. How might females distinguish each other? How can this be tested?
Olfactory or sonic cues
Obtain a long-associated, reciprocal pair, separate them, expose each to the other’s scent or vocal recordings, see what provokes a behavioural response
Wilkinson found that female vampire bats social groom. In what year did he find this?
1986
Wilkinson, 1986:
Females bats social groom. When? Why is this important?
Grooming occurs before regurgitation and is correlated to regurgitation frequency.
This can be used as a way to identify non-reciprocators.
How can experiments that focus on grooming give information about reciprocation?
Measure the association between grooming and regurgitation, see whether they are correlated.
Females may identify individuals to share with by grooming.
Who looked at captive studies on just males? What happened?
Wilkinson, 2013:
An all-male captive group began sharing with each other after some time, supports reciprocal altruism as there is guaranteed pay-off to helping non-relatives.