Reciprocal altruism in bats

Question 1

Who conducted the initial studies on the common vampire bat?

Answer 1

Wilkinson, 1984

Question 2

What is the latin name for the common vampire bat?

Answer 2

Desmodus rotundus

Question 3

What did Wilkinson (1984) find?

Answer 3

That bats regurgitate blood meals to save roost mates from starvation

Question 4

In what three ways could you describe the regurgitation behaviour of bats?

Answer 4

1. Group selection
2. Kin selection
3. Reciprocal altruism

Question 5

Where were the experiments on D. rotundus carried out? For how long?

Answer 5

Northwest Costa Rica for 26 months

Question 6

Which sex is philopatric in D. rotundus?

Answer 6

Females

Question 7

Do females move between roosting sites?

Answer 7

Yes

Question 8

Do males associate with females?

Answer 8

No

Question 9

How many roosting sites were involved in the study?

Answer 9

14

Question 10

What was the population of D. rotundus estimated at? How many individuals were ID tagged?

Answer 10

Estimated at 200, 184 were tagged

Question 11

How was relatedness assessed?

Answer 11

Direct observation of mothers nursing their offspring

Question 12

When was regurgitation observed?

Answer 12

When roost mates had failed to obtain a blood meal for themselves

Question 13

How did capture experiments confirm the cause of sharing?

Answer 13

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.

Question 14

In which age category was failure to obtain a blood meal more common? Why?

Answer 14

Younger bats, presumably due to hunting inexperience

Question 15

What is group selection?

Answer 15

Where group selection acts on a group as a whole, rather than on individuals.

Question 16

What does group selection require?

Answer 16

Cooperation of all individuals within the group to behave ‘for the good of the group’.

Question 17

Group selection favours populations of…

Answer 17

altruists

Question 18

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?

Answer 18

110

77

21

Question 19

How can group selection be used to explain blood meal sharing?

Answer 19

Bats shared with unrelated individuals as it increased survivorship of the entire group as less members die of starvation

Question 20

What disproves group selection as the reason for blood meal sharing in bats?

Answer 20

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)

Question 21

Why are males excluded from sharing?

Answer 21

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

Question 22

Why is group selection a contentious theory? Give 2 reasons.

Answer 22

1. Natural selection relies on random mutations with unforeseen effects in response to environmental changes. Under group selection groups systematically change their strategy.
2. 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.

Question 23

What is kin selection?

Answer 23

The preference for relatives due to inclusive fitness (shared genes by descent)

Question 24

How can kin selection be used to explain regurgitation in bats? Refer to Hamilton’s rule.

Answer 24

77 cases between related individuals were observed. Relatedness between mother and offspring = 0.5, thus it is possible that rb > c

Question 25

Why is kin selection not responsible for regurgitation in bats? Refer to Hamilton's rule.

Answer 25

21 cases were observed between non-related individuals, where r = 0. Thus it is likely that rb

Question 26

Why would a mother want to save her starving offspring?

Answer 26

So the offspring can go onto proliferate the mother's genes, is actually a selfish act

Question 27

Why might 77 cases of mother-offspring regurgitation have been observed, NOT because of relatedness?

Answer 27

Because of close association and proximity; mothers and daughters roost next to each other

Question 28

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?

Answer 28

Because younger bats are inexperienced at hunting and more likely to need rescuing than adult roost mates

Question 29

What is reciprocal altruism?

Answer 29

When an individual commits a selfless act with the expectation of future payback

Question 30

What is reciprocal altruism based on?

Answer 30

Repeated interaction

Question 31

What are the three conditions required for reciprocal altruism?

Answer 31

1. Repeated, pair-wise interaction 2. Benefit must exceed cost 3. Non-reciprocators can be identified and avoided

Question 32

How do we know bats have repeated pair-wise interactions, indicating reciprocal altruism?

Answer 32

They roost with the same individuals for years and can live up to 18 years old, presenting lots of opportunities for reciprocity

Question 33

How do we know benefits exceed costs, indicating reciprocal altruism?

Answer 33

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.

Question 34

How do we know non-reciprocators are identified and not shared with, indicating reciprocal altruism?

Answer 34

Males are not shared with as they do not reciprocate blood meals

Question 35

How can males be distinguished from females?

Answer 35

They are smaller, presumably also olfactory and sonic differences

Question 36

How could we prove regurgitation is attributed to reciprocal altruism with further tests? What two things would need to be tested?

Answer 36

That conditions for reciprocal altruism are always filled: 1. That repeated pair-wise interaction leads to RA 2. That non-reciprocators are identified

Question 37

How would we test for repeated pairwise interactions that lead to RA?

Answer 37

1. Wild behavioural focals 2. 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) 3. Captive studies between unrelated and related groups that are then mixed

Question 38

Explain how captive studies between unrelated and related groups that are then mixed would indicate RA. What would we assume under RA?

Answer 38

(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

Question 39

Males are easily identified as non-reciprocators due to sexual dimorphism. How might females distinguish each other? How can this be tested?

Answer 39

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

Question 40

Wilkinson found that female vampire bats social groom. In what year did he find this?

Answer 40

1986

Question 41

Wilkinson, 1986: Females bats social groom. When? Why is this important?

Answer 41

Grooming occurs before regurgitation and is correlated to regurgitation frequency. This can be used as a way to identify non-reciprocators.

Question 42

How can experiments that focus on grooming give information about reciprocation?

Answer 42

Measure the association between grooming and regurgitation, see whether they are correlated. Females may identify individuals to share with by grooming.

Question 43

Who looked at captive studies on just males? What happened?

Answer 43

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.