Social Behavior Flashcards
1
Q
What is a social behavior?
A
Any behavior with fitness consequences for both the individual that performs it (actor) and another individual (recipient)
2
Q
Table classifying social behaviors
A
3
Q
A behavior that has a positive effect on both the actor and the recipient is ___
A
Mutualistic
4
Q
A behavior that has a positive effect on the actor but a negative effect on the recipient is ___
A
Selfish
5
Q
A behavior that has a negative effect on the actor but a positive effect on the recipient is ___
A
Altruistic
6
Q
A behavior that has a negative effect on both the actor and the recipient
A
Spiteful
7
Q
Kin selection and inclusive fitness
A
- We can quantify the probability that a specific copy of a gene (allele) in a parent is present in one of its offspring
- r: the coefficient of relatedness
- The likelihood individuals share an identical gene because it was inherited from the same ancestor
8
Q
Calculating r
A
- In diploid species (those where each cell contains two complete sets of chromosomes, one inherited from each parent), each offspring receives half its genes from each parent
- Each parents shares half of its alleles (variant of a gene) with a child
- We say that parents and offspring are related by 1/2, r=1/2
- Any two siblings are also related by 1/2
- Each sibling receives half its alleles from each parent
- Siblings could share no alleles (unlikely, would happen if both children got the half of the alleles from each parent that the other didn’t)
- Siblings could share all aleles (also unlikely, in the case both children got the same sets of alleles from each parent)
- But on average, siblings share half their alleles, so r=1/2
9
Q
How can we calculate r for other relatives?
A
10
Q
The implications of relatedness for altruism
A
- Offspring are not the only relatives to share copies of the same gene by descent (siblings, r=1.5, cousins, r=0.125
- Bill Hamilton realized: a given gene can proliferate if a parent cares for its offspring, by increases its chances of survival, but also by caring for siblings, cousins, or other relatives
There are two ways for a gene to increase transmission to the next generation:
1) Incrase the reproductive success of the individual which it is in
2) Increase the reproductive success of other individuals who carry copies of that gene
11
Q
Kin selection
A
- Natural selection on genes will lead to individuals behaving in ways that maximise their inclusive fitness rather than on only their direct reproductive success
- Termed ‘kin selection’ by John Maynard Smith: the process by which characteristics/behaviors are favored due to their effects on relatives
12
Q
Inclusive fitness = ___ + ___
A
Direct fitness + indirect fitness
13
Q
Hamilton’s Rule
A
- Describes the conditions under which an altruistic act will spread due to kin selection
- Imagine an interaction between an altruist (actor) and a recipient
- The costs and benefits of the interaction are in terms of the survival chances of the actor and the recipient (e.g. giving an alarm call, feeding it, saving someone from drowning)
14
Q
Calculation for Hamilton’s Rule
A
15
Q
Example of Hamilton’s rule
A
- Imagine a gene that programs an individual to die in order to save the lives of relatives
- If the altruist dies, one copy of the gene is lost from the population (C=1)
- BUT, the gene could still increase in frequency in the gene pool if, on average, the altruistic act saves the lives of more than two brothers or sisters (r=0.5)
- Because: B/C > 1/r -> B/1 > 1/r -> B > 1/0.5 -> B > 2
How many cousins (r = 0.125 or 1/8) would need to
be saved to satisfy Hamilton’s Rule?
B/C > 1/r -> B/1 > 1/r -> B > 1/0.125 -> B > 8
16
Q
Altruism between relatives in Belding’s Ground Squirrel
A
- Hibernate in winter and emerge above ground in May
- Soon after emergence, females mate
- After mating, males wander off and females rear young alone
- To do this, females establish a territory around a nest burrow
- When pups wean, males disperse and female pups remain close in the natal area
- Males seldom (if ever) interact with close relatives, but females spend their whole lives surrounded by close female kin
- Closely-related females seldom fight for nest burrows or chase another from territories – cooperate to defend young
- About 8% of yound are dragged from the burrow and killed by other squirrels, but the killers are never close relatives of the victim
- Unrelated females sometimes attempt to take over burrows
- Pattern of cooperation among close relatives/conflict among unrelated individuals
17
Q
Alarm calls in Belding’s Ground Squirrels
A
- Individuals give alarm calls whenever a predator approaches
- Callers suffer a cost from giving the alarm because they are more likely to be attacked by a predator
- Other individuals in the group benefit by being more likely to escape
- Sherman showed that:
- Females are much more likely than males to give alarm calls
- Females with close relatives nearby were more likely to give alarm calls than females without
- Females gave alarm calls when only offspring were around and ALSO when only parents or non-descendent relatives were nearby
18
Q
Competitive courtship in wild turkeys: turkey ‘wingmen’
A
- Groups (2-4) of same-aged males sometimes form coalitions to court females and defend those females from other males
- In a coalition, one male is the dominant male (all the mating) and the other is subordinate (no mating)
19
Q
What are the coefficients in Hamilton’s rule?
A
Hamilton’s rule: rB-C
r: coefficient of relatedness
B: benefit to dominant
C: cost to subordinate
20
Q
Variable B
A
Benefit to dominant (# extra young produced due to subordinate’s help)
Calculation: Mean # offspring produced per dominant - mean # offspring produced per solitary
21
Q
Variable C
A
Cost to subordinate (# own young sacrifice to help dominant male)
Calculation: Mean # offspring produced per solitary - mean # offspring produced per subordinate (0)
22
Q
Variable r
A
Coefficient of relatedness
Calculation: mean pairwise relatedness of subordinates to dominant partner
23
Q
How do individuals recognize kin?
A
- For Hamilton’s rule to work, animals need to know which individuals are close kin
- This is called ‘kin discrimination’: an individual assesses the relatedness to other individuals and adjusts its behavior accordingly
24
Q
Greenbeards
A
- There may be ‘recognition alleles’ that express their effects phenotypically
- Anyone bearing this allele would have a certain phenotype (a trait, or ‘green beard’)
- Anyone bearing this trait could then recognize others that have the allele
- And bearers of the allele could then direct altruistic behavior towards others with the trait
For this to work, a gene needs to:
- Signal itself (phenotypically manifest
- Recognignize the signal in others (notice/assess when the others have the signal)
- Direct cooperation individuals in which it detects the signal
25
Greenbeard genes in the fire ant
- Fire ant nests contain multiple queens
- New queens are recruited into the nest after they mate
Green beard gene is Gp-9 locus
- Workers with the b allele use odor to determine if the prospective queens also carry the b allele (and decapitate them if they don't)
- This benefits queens with the b allele, who are recruited and don't have to compete for resources with females who don't carry it (since queens that don't carry it aren't allowed in)
26
But, greenbeards are likely rare, because:
1) They're very complex
2) They're prone to invasion by cheaters (who display the green beard without also being altruistic)
27
Direct Genetic Kin Discrimination and 'Armpits'
- Use kinship as a proxy for sharing genes: if you recognize kin, you have recognized an individual with whom you likely share genes
- Can sometimes recognize kin based on direct genetic cues that are recognized phenotypically
- For example, if some aspect of scent is genetically determined, more closely related individuals will smell more similar
- Rule for kin discrimination could be: 'be altruistic to neighbors who smell similar to you'
- Richard Dawkins called this the 'armpit effect'
28
Example of altruism from slime molds
- Individuals live in the soil & feed on bacteria
- When starved, cells aggregate in the thousands to form a multicellular motile 'slug' form that migrates to the surface and transforms in to a fruiting body
- Fruiting body = stalk that holds up a ball of spores
- The cells in the spores reproduce - cells in the stalk die without reproducing
- Being a stalk cell is an example of extreme altruism
29
Example of how environmental cues can also aid kin discrimination
- Parent birds may ignore their own young if they are placed just outside the rim of their nests, but will readily accept a strange chick placed inside their nest
30
Kin selection without kin discrimination
- Kin selection by kin discrimination: individuals discriminate who is and who is not kin, and exhibit behaviors that favor their kin's survival and reproductive success
- But, it is possible for kin selection to operate without kin discrimination: even if you can't recognize who is kin or not, natural selection could still fine tune behaviors that result in increased survival and reproductive success in kin
- Limited dispersal
E.g. neighbors are more likely to be kin = you're more likely to share food w neighbors
Phenotypic similarity
More likely to favor those who look like you
Group membership
More likely to favor those who are part of your ‘group’
31
Kin selection beyond altruism
- Hamilton noted that his rule could for any social behavior: individuals should value any positive or negative consequences for recipients of a behavior according to the coefficient of relatedness to them
Consider a hypothetical selfish behavior:
- It provides a benefit to the actor, but is costly to the recipient
- Hamilton predicted that individuals should show greater restraint (resist performing the selfish behavior) when interacting with closer relatives
- Because harming a relative would decrease the relative's ability to transmit shared genes, resulting in an indirect fitness cost
32
Cannibalism: the ultimate selfish behavior
- Arizona tiger salamanders
Larvae occur in two morphs:
- Typical morph: feeds on invertebrates
- Cannibal morph: has specialized oral structures for eating other larvae
- Cannibal morph occurs more frequently when salamander larvae exist in higher densities, and when food is more limited
Researchers tested whether development into the cannibal morph was influenced by whether larvae interacted with relatives or non-relatives
- Inclusive fitness theory: cannibalism is less likely to be favored when interacting with relatives - eating a relative would = indirect fitness cost
- Researchers reared larvae in groups of 16. Groups were either all siblings or a mixture of kin and non-kin
Results:
- Larvae were significantly less likely to develop into cannibals when in a group of siblings or other close relatives
- When housed in a mixture of siblings and non-siblings, cannibals preferentially consumed non-siblings
Can an alternative hypothesis explain these results?
- Is cannibalizing non-kin an avoidance strategy?
Found:
- Cannibals were not more likely to become infected by eating kin
- Cannibals did not avoid diseased prey
- Results were actually opposite of predicted: survival was higher when eating siblings
33
Spite: the dark side of Hamilton's rule
- Hamilton's rule can also show us how selection can favor spiteful harming behaviors, which are costly to both actor and recipient
- C is positive (costly to actor), B is negative (costly to recipient)
- Given the costs to both parties, for rB-C>0 to occur, relatedness has to be negative
- Negative relatedness just means that the recipient of the behavior is less related to the actor than the average member of the population
- Imagine a gene that codes for spiteful behavior. If harming an individual who does not carry the spiteful gene frees up resources (or reduces competition) in a way that benefits individuals who DO carry the spiteful gene, this gene can spread
Spite is favored when it can be directed at non-relatives, and when the harming of non-relatives benefits the actor's relatives
