Social Behaviour; Reproductive Behaviour

Question 1

True or false. The “social behaviour” unit focuses only on intraspecific (within-species) interactions

Answer 1

True

Question 2

Name the four types of intraspecific social interactions we discussed in class?

Answer 2

1. Spiteful behaviour
2. Selfish behaviour
3. Cooperative behaviour
4. Altruistic behaviour

Question 3

What is “spiteful” behaviour?

Answer 3

An interaction that is negative to both the actor and the recipient / other individuals of the same species ( - / - ).

Thought to be very rare. e.g. suicide bomber, eating your own young. Mountain sheep exposing themselves to predation risk to keep their competitors from recovering and going back up the mountain after an injury.

Question 4

What is “selfish” behaviour?

Answer 4

An interaction that is beneficial for the actor (+) but harmful to the recipients / other individuals of the same species ( - )

e.g. infanticide in lions for babies unrelated to them.

Question 5

What is “cooperative” behaviour?

Answer 5

An interaction that is beneficial to the actor (+) and the recipients / other individuals of the same species (+)

e.g. group hunting in social spiders

Question 6

What is “altruistic” behaviour?

Answer 6

An interaction that is negative to the actor ( - ) but beneficial to recipients / other individuals of the same species ( + ).

e. g. helpers caring for offspring of breeding pair sacrifice their own reproduction temporarily to help raise their younger siblings.
e. g. alarm calling
e. g. eusocial workers

Question 7

Name and describe the four hypotheses for why cooperation and altruism evolve.

Answer 7

1. Mutualism : both parties do in fact benefit in some way
2. Manipulation : actors are only acting beneficially because they are being manipulated in some way to do so. This means they are being forced to help, and it’s out of their control. e.g. queen ants release hormones to reproductively suppress other ants in the colony, so that they can focus more on supporting the colony.
3. Reciprocity : It has evolved because the helpful act is thought to be reciprocated to you at a later time when you need it.
4. Kin Selection : Actors help because individuals are related. Increasing the fitness of relatives makes up for the cost to the actor.

Question 8

What are some assumptions for the “reciprocity” hypothesis for the evolution of altruism and cooperation?

Answer 8

• The actor and recipient need to have repeated encounters for it to be reciprocated
• The actor and recipient need to have the ability to recognize each other from other individuals
  e. g. vampire bats give blood meals to starved individuals, and it may be reciprocated to the actor later on.

Question 9

True or false. “Reciprocity” hypothesis can explain the evolution of altruism in non-relatives

Answer 9

True.

Question 10

Why are ground squirrel FEMALES more likely to do alarm calls?

Answer 10

Because in ground squirrels, the females are often related to one another, while the males aren’t, so the females may have the incentive to help their colony because they are more related to members of the colony than males.

Question 11

The hypothesis “Kin selection” has a formula, called ______ ______.

Answer 11

Hamilton’s rule.

Question 12

What is the equation for Hamilton’s rule and what does it represent?

Answer 12

Hamilton’s rule states that a gene for altruism will spread due to kin selection if…

rB - C > 0

Where:

r is the relatedness of the actor to the recipient
B is the benefit to the recipient
C is the cost to the actor

Question 13

True or false. According to Hamilton’s rule, as r, the relatedness of the actor to the recipient, increases, so too does the probability of the spread of the altruistic gene due to kin selection.

Answer 13

True

Question 14

Define inclusive fitness

Answer 14

When we think of natural selection, we think of what animal has greatest personal fitness.

When we think of kin selection, we think of what animal has greatest inclusive fitness.

Inclusive fitness is a component of kin selection;
a theory given to explain the evolution of altruistic or cooperative behaviour.

In inclusive fitness, we focus on both the effect of the altruistic behaviour on direct fitness (on you, your reproductive success), and also its effects on indirect fitness (HOW YOUR HELP effects the reproductive success of relatives MULTIPLIED BY THE DEGREE OF RELATEDNESS)

Question 15

How is kin selection different from inclusive fitness?

Answer 15

Inclusive fitness is a component of kin selection, just like how regular fitness is a component of natural selection

Question 16

Leticia’s paper that we read had genes that were grouped into two categories, based on two types of behaviour. what were they?

Answer 16

Genes were categorized as having influence on…

1. grouping tendencies / behaviour
2. cooperative tendencies / behaviour

Question 17

What is multi-level selection and how does it differ from kin selection?

Answer 17

Multi-level selection means selection that can occur at many levels - genes, organelles, species, cells…In terms of how altruism and cooperation evolved, it focuses on within and between group selection. Unlike kin selection, it also explains how these kinds of behaviour evolve in NON-relatives, covering all other hypotheses - mutualism, reciprocity, kin selection…

Question 18

True or false. Selection can happen at many levels e.g. at the level of the cell, the genes, or the species, as long as they follow Darwin’s four postulates:

1. there is variation
2. variation is heritable
3. some forms are more fit than others
4. there’s a turnover

Answer 18

True

Question 19

What levels of selection does multi-level selection focus on in the context of the evolution of cooperation or altruism?

Answer 19

Selection within groups (within-group selection) and selection between different groups (between-group selection).

Question 20

How would Darwin’s four postulates apply to within-group selection?

Answer 20

1. genetic variation within individuals of a group
2. Individuals can give rise to other similar individuals (heritability)
3. some individuals are more fit than others in a group
4. There’s a turnover of individuals within a group, replaced by other individuals

Question 21

How would Darwin’s four postulates apply to between-group selection?

Answer 21

1. genetic variation between groups
2. Groups can give rise to other similar groups (heritability)
3. some groups are more fit than others
4. There’s a turnover of groups, replaced by other groups

Question 22

Define:

a) freeloaders

b) cheaters

Answer 22

a) freeloaders are individuals that have a high tendency for grouping, but low tendency for cooperation
b) cheaters are individuals that have a low tendency to group, low tendency to cooperate

Question 23

True or false. When cooperation is not costly, grouping and cooperation evolve rapidly. If it’s costly, cooperation evolves a lower rates.

Answer 23

True

Question 24

Page 40.
You have a graph with relative fitness on the y-axis, cooperative tendency of an individual on the x-axis (in a range of 0-1, 0 being not cooperative at all, and 1 being extremely cooperative).

How would the function look like if there was no cost to cooperate? (Also referred to as mutualism)

(Note that in this kind of function, the cost to cooperate is represented by the slope.)

Answer 24

The curve would be a horizontal line at relative fitness 1.

In other words y = 1 across all x-coordinates.

Question 25

Page 40.
You have a graph with relative fitness on the y-axis, cooperative tendency of an individual on the x-axis (in a range of 0-1, 0 being not cooperative at all, and 1 being extremely cooperative).

How would the function look like if there was an intermediate cost to cooperate? e.g. B = 0.4

(Note that in this kind of function, the cost to cooperate is represented by the slope.)

Answer 25

It will be a linearly decreasing function. The more cooperative you are, the more costs on your fitness.

The slope would be 0.4.

Question 26

Page 40.
You have a graph with relative fitness on the y-axis, cooperative tendency of an individual on the x-axis (in a range of 0-1, 0 being not cooperative at all, and 1 being extremely cooperative).

How would the function look like if there was a high cost to cooperate? e.g. B = 0.8

(Note that in this kind of function, the cost to cooperate is represented by the slope.)

Answer 26

It will be a linearly decreasing function. The more cooperative you are, the more costs on your fitness.

The slope would be 0.8, much steeper than if the cost for cooperation was intermediate.

Question 27

If freeloaders and cheaters can avoid the cost of cooperation, why don’t they take over groups permanently?

Answer 27

Because having a lot of freeloaders or cheaters in a group lowers GROUP PRODUCTIVITY.

Lower group productivity is what prevents them from taking over.

Question 28

True or false. Freeloader frequencies oscillate over time. Sometimes they are rare in a group, sometimes they are common.

Answer 28

True

Question 29

When freeloaders are at high levels (i.e. are common in a group),

a) what’s the effect on group productivity?
b) What happens to the frequency of freeloader genes in this population at this point in time?
c) Selection matters at what level, within or between groups?

Answer 29

When freeloaders are at high levels in a group…

a) They significantly lower group productivity
b) a lower group productivity significantly reduces the frequency of freeloader genes in the population
c) selection matters at the level of between-groups

Question 30

When freeloaders are at low levels (i.e. are rare in a group),

a) what’s the effect on group productivity?
b) What happens to the frequency of freeloader genes in this population at this point in time?
c) Selection matters at what level, within or between groups?

Answer 30

When freeloaders are at low levels in a group…

a) they have very little effect on group productivity
b) because of the advantage they get from other cooperative members, the frequency of freeloader genes increases in the population
c) selection matters at the level of within-groups

Question 31

What component of multilevel selection is responsible for preventing the freeloaders/cheaters taking over? Within-group selection of between-group selection?

Answer 31

Between-group selection. Groups with more freeloaders have lower productivity than groups with fewer freeloader members

Question 32

If the rate of turnover of groups is greater than the rate of turnover of individuals within groups, which is more important in the evolution of cooperation: Within-group selection of between-group selection?

Would cooperation evolve?

Answer 32

Between-group selection

Cooperation would evolve because between-group selection favours more productive groups with fewer freeloaders.

Question 33

If the rate of turnover of individuals is greater than the rate of turnover of groups, which is more important in the evolution of cooperation: Within-group selection of between-group selection?

Would cooperation evolve?

Answer 33

Within-group selection. The rate of turnover is too slow between groups.

Cooperation would not evolve, because within-group selection favours individuals with higher fitness i.e. the freeloaders.

Question 34

If the cost of cooperation is greater among individuals than between groups, which is more important in the evolution of cooperation: Within-group selection of between-group selection?

Would cooperation evolve?

Answer 34

Within-group selection, cooperation may be less likely to evolve, because within-group selection favours individuals with higher fitness i.e. the freeloaders.

Question 35

If the cost of cooperation is greater between groups compared to within individuals, which is more important in the evolution of cooperation: Within-group selection of between-group selection?

Would cooperation evolve?

Answer 35

Between-group selection.

Cooperation more likely to evolve because between-group selection favours more productive groups with fewer freeloaders.

Question 36

If there’s high genetic variance among individuals, but low genetic variance between groups, which is more important in the evolution of cooperation: Within-group selection of between-group selection?

In this case, would cooperation evolve?

Answer 36

Individuals within groups are very diverse, so within-group selection would be more important.

In this case, cooperation is less likely to evolve.

Question 37

If there’s low genetic variance among individuals, but high genetic variance between groups, which is more important in the evolution of cooperation: Within-group selection of between-group selection?

In this case, would cooperation evolve?

Answer 37

Individuals within groups are pretty similar, but the genetic difference between different groups is quite dissimilar. Between-group selection would be more important.

In this case, cooperation would be more likely to evolve.

Question 38

Why is it more likely for cooperation to evolve when we have high between group genetic variance, but low individual (within group) variance?

Answer 38

One of the rules of selection is that we need high genetic variance for it to work.

If we had high within-group variance, and low between-group variance, within-group selection would be the one active.

Within groups, freeloaders have a greater fitness than cooperative members, so within-group selection would favour them, and cooperation would not evolve.

In contrast, when between-group variance is higher, the productivity of the group becomes important (group fitness). Freeloaders reduce the productivity of the group, so between-group selection would select against groups with many freeloaders. This will favour cooperative groups, and favour the evolution of cooperation.

Question 39

What is Hamilton’s r?

Name the formula and explain how it works

Answer 39

A math statistic, ranging from 0 to 1, that predicts whether between-group selection is more important or within-group selection. Hamilton’s r is mostly used for groups consisting of relatives.

r = between-group variance / total variance

if r is closer to 0, it means between-group variance is low, and within-group selection is more important - cooperation unlikely to evolve

if r is closer to 1, it means between-group variance is high, and between-group selection is more important - cooperation likely to evolve.

Question 40

According to Leticia, there are two ways for cooperation to evolve in non-kin, what are they?

Answer 40

• if there’s no cost to cooperation

- if the helping roles are assigned randomly like a lottery

Question 41

Why was between and within group selection initially controversial?

Answer 41

Because of careless statements that used within and between group selection to explain how animals would care for the survival of the species.

Animals only care about their own survival, and possibly their relatives, because of the benefits it gives to themselves. They do not care about the survival of the species.

Question 42

True or false. Males and females often have different roles in reproduction

Answer 42

True

Question 43

Males and females often have different roles in reproduction because of _________. Females are often ________, males are often _______

Answer 43

Anisogamy

females - choosy

males - competitive

Question 44

What is anisogamy? What are the two consequences of anisogamy?

Answer 44

Anisogamy is when females and males have different sized gametes. In most animals the female gametes are bigger. This results in females having a greater investment per offspring compared to males.

Two consequences of anisogamy:

1. Females are limited by the number of offspring they can produce because of increase investment per offspring
2. Males are limited by the number of sexually-available females.

Question 45

What is Bateman’s principle? Give an example of an animal system using Bateman’s principle

Answer 45

Bateman’s principle claims that…

1. Males have higher variance in reproductive success (number of matings) than females. Some males mate a lot, others don’t at all.
2. Males can have more offspring the more they mate, but females cannot increase the number of offspring they produce by increasing the amount they mate.
   e. g. Just 4% of male elephant seals sire 85% of the progeny in a population.

Question 46

Under what conditions can the sex roles be reversed?

Give examples.

Answer 46

If males are more invested in the offspring than females, they are the ones who are choosy and females are the ones who are competitive.

Giant water bug males carry eggs on their backs

Question 47

Define the operational sex ratio (OSR)

Answer 47

The ratio of sexually-receptive males to sexually-receptive females at the time of mating.

Question 48

True or false. We see these differential sex roles between females and males only in the operational sex ratio is 1:1.

Answer 48

True

Question 49

True or false. In some cases, the OSR (operational sex ratio) can change

Answer 49

True

Question 50

In the two-spotted goby, the operational sex ratio can change. Explain what happens when it changes

Answer 50

The OSR of the two-spotted goby is seasonal, shifting from male-biased (more males) to female-biased (more females). When it is male-biased, males are the ones courting females because they are the limiting resource. When it is female-biased, females are the ones courting males because they are the limiting resource.

Question 51

Define sexual selection

Answer 51

A type of natural selection that selects for traits that increase reproductive success, in either sex.

Question 52

True or false. Sometimes sexual selection is detrimental or costly, but sexual selection is still seen because the benefits it affords to reproductive success is worth the costs.

Answer 52

True

Question 53

In species where males compete more (e.g. polygynous species), species selection is quite intense – greater sexual _______, more ornamented or brightly coloured males.

Answer 53

sexual dimorphism

Question 54

Sexual selection comes in two forms, what are they?

Answer 54

1. Intrasexual selection (i.e. male-male competition)

2. intersexual selection (i.e. female choice)

Question 55

Male-male competition, or intra-sexual selection can happen…

(1) pre-copulation
(2) post-copulation
(3) post-fertilization

Give examples for each

Answer 55

1. pre-copulation
   e. g. red-winged blackbirds set up territories to compete for females
   e. g. deer fight one another with antlers for the female
2. post-copulation
   e. g. damselflies hold on to females after copulation to prevent access to her by other males.
   e. g. some ornithoptera produce genital plugs that prevent other males from mating with the female they mated with
3. post-fertilization
   e. g. infanticide in lions, langur monkeys

Question 56

What is intersexual selection or female choice?

Answer 56

this is a component of sexual selection in which traits that are costly to males are selected for because females choose them.

Question 57

Name the two hypotheses that explain why females choose costly traits for their mates

Answer 57

1. The sexy son hypothesis/Fischer’s runaway selection

2. The good genes hypothesis/Handicap principle

Question 58

Describe the sexy sons hypothesis/Fischer’s runaway selection

Answer 58

Females prefer traits on males that will make their sons attractive. With this hypothesis, the trait females prefer get exceedingly exaggerated, till it surpasses the optimal trait value (runaway) and begins hindering male survival.

The trait value will eventually stop at where the strength of natural selection equals the strength of sexual selection, the trait value cannot go any further or natural selection will kick in and kill off the male.

Question 59

True or false. In the sexy sons hypothesis/Fischer’s runaway selection, females want more and more exaggerated traits (runaway) up until the point the strength of natural selection matches the strength of sexual selection and prevents it from getting any more exaggerated.

Answer 59

True

Question 60

What two assumptions does the sexy sons hypothesis/Fischer’s runaway selection have?

Answer 60

1. ) Female choice must be open-ended (females just want more and more exaggerated traits)
2. ) The trait that is getting exaggerated must be heritable

Question 61

How would you experimentally test for the sexy sons hypothesis / fischer’s runaway selection?

Answer 61

The trait value of males and female choice should be correlated e.g. if the trait was eye stalk length, females that prefer shorter stalks should pick males with shorter stalks, and females that prefer longer stalks should pick males with longer stalks.

To prove it is heritable, we also need to connect a correlation between parents and offspring. We could do a correlation showing daughter’s preference and the trait value of her father.

Question 62

Describe the good genes hypothesis / Handicap principle

Answer 62

Females choose for costly exaggerated traits because they are an honest indicator of some other trait that shows high fitness in males. According to the handicap principle, only the males that are of highest quality (genetically) can survive such exaggerated traits that are a handicap to them.

Question 63

What is honest signalling theory

Answer 63

In order for the good genes hypothesis to work, the exaggerated trait needs to be an honest indicator of male genetic quality. it can’t be a trait all males have

Question 64

What are the assumptions for the good genes hypothesis / Handicap principle?

Answer 64

• trait has to be costly (Zahavi’s principle)

- the trait that is exaggerated and the trait that improves fitness both need to be heritable

Question 65

How would you experimentally test for the good genes hypothesis / Handicap principle?

Answer 65

• prove the exaggerated trait is costly
• show that the exaggerated trait has a correlation to a trait that improves fitness in both the males that have it and their offspring

An example of the good genes hypothesis tested: In this study, first they checked to see if Barn swallow tail length is costly. They artificially elongated the tails of some males and found that in the next season they grew shorter tails, meaning there must be a cost for carrying this extra length (i.e. it needs to be a handicap). Then they tested to see if this trait, tail length, was correlated with another trait that has something to do with fitness, in this case the number of mites on offspring. Their results found a correlation between longer tailed fathers and healthier offspring with fewer mites.

Question 66

Males and females often want different things from reproduction, which results in sexual conflict. Name and describe the four factors that result in sexual conflict between males and females

Answer 66

1.) Mating decisions:
Females decision to mate or not is more strict than males, because females have a lot more to lose by mating with the wrong partner. Males don’t really struggle in this area because they invest so little, that they can just move on to the next mate. Males may want to mate, but females will be more hesitant

2.) Offspring care:
offspring care is costly, so females want to leave offspring care to males, and males want to leave it to females.

3.) Infanticide:

 Infanticide might be beneficial for males because it reduces competition with other males, but it's always detrimental to females because they lose their reproductive investment

4.) Multiple matings:

According to Bateman's principle, females TYPICALLY gain little from multiple matings, because the amount of offspring they produce is limited. Males will want to mate multiple times, but females may not be interested

Question 67

Why do we have cases of antagonistic coevolution or arms races between the two sexes?

Answer 67

Because of sexual conflict

Question 68

Give two examples of antagonistic coevolution between males and females in the context of reproduction.

Answer 68

Mallard species would force themselves on females to copulate, so females evolved long spiral reproductive ducts to prevent the forced copulation. In response, males have evolved long spiral phallic organs to be able to copulate with them, spiraling in the opposite direction.

Water strider males have structures to hold on to females, and females have traits to resist males and make it difficult for them to hold on to them.