1.3: Sex and Sexual Selection

Question 1

Asexual reproduction/gynogenesis

Answer 1

100% reproduction of the genome

Question 2

Why is asexual reproduction more efficient than sexual reproduction?

Answer 2

Because if a fit individual reproduced asexually, they would produce offspring equally as fit

Question 3

Give three reasons why sexual reproduction is more frequent that asexual reproduction? And state the reason sex evolved.

Answer 3

Sex increases variability
Sex increases competition and selection
Sex increases rates of evolution

Sex did not evolve for reproduction, it evolved to accelerate adaptive evolution

Question 4

Name and explain fours theories on the evolution of sex.

Answer 4

Tangled Bank hypothesis: variation in offspring matches variation in the environment, and reduces competition between offspring so they can survive and reproduce

The lottery principle: the environment changes in unpredictable ways, so it is beneficial for offspring to vary so some may survive the changes and reproduce

The red queen hypothesis: greater variation in offspring increases the likelihood of evolving resistance to pathogens

Removing deleterious mutations: sexual reproduction shuffles genes, which increases the likelihood of giving some offspring only beneficial mutations and some only deleterious mutations, meaning that only the beneficial mutations will survive

Question 5

Why is hermaphroditism is not a stable strategy?

Answer 5

There is competition between sexes
Therefore it becomes about donating sperm, rather than fertilising their own eggs
Multiple copulation makes the female role too expensive
It is more advantageous to assume the male role
Therefore cheating strategies develop among hermaphrodites

Question 6

Give three example of cheating strategies that hermaphrodites use

Answer 6

Structures of digesting spermatozoids after copulation
Secretion of hormones that induce ovulation in the partner
Destroying partner’s ejaculatory organ

Question 7

Why is there a balanced sex ratio?

Answer 7

The best strategy is specialising
The ratio is reached because the least numerous sex with have higher expected fitness and will therefore increase in number to form the equilibrium

Question 8

Why are females more interested in the success of a zygote than males?

Answer 8

Eggs (the larger gamete) are more expensive than sperm
Female has the physiological cost of pregnancy; gestation and lactation cost on average 800,000 calories if the child is exclusively breastfed for 2 years
Male reproduction is cheap and highly successful; the cost of producing millions of spermatozoids is low

Question 9

What are the two limitations to male reproduction?

Answer 9

How many females will be fertilised

Fatherhood uncertainty; male cannot be sure offspring carry his genes

Question 10

Which sex offers the most parental care in mammals?

Answer 10

90% of mammal species are characterised by provisioning females and absent males

Question 11

Is optimal offspring number the same between sexes?

Answer 11

No

Females invest more so their optimal offspring number is smaller

Question 12

Why is there sexual selection? (2)

Answer 12

Differential investment implies that adaptions defining the fittest female differ from those defining the fittest male

To produce sexual dimorphism

Question 13

What is the difference in reproductive aims and strategies between the sexes?

Answer 13

Aims: Females aim to maximise quality of fertilisations, Males aim to maximise quantity of fertilisations

Strategies: Females maximise quality of partner through mate choice, Males maximise quantity of partners through male competition for female monopoly

Question 14

What is the Handicap Principle (Zahavi, 1975)? Give three examples.

Answer 14

Male incurs costs to advertise quality of genes

Male peacock’s fine tail plumage displays strength in times of food resource stress
A threatened gazelle will jump extremely high to display strength but draw a lot of attention from predators
White pelican develop bulges at the base of the beak during mating season that impairs its ability to see and fish

Question 15

How do ecological conditions determine which sex prevails? Describe how males can be more selective and how females can adapt.

Answer 15

Males monopolise females by controlling territories where they depend of limited/localised food sources and breeding sites
Females can adapt by cheating or controlling sex ratio

Question 16

How do ecological conditions determine which sex prevails? Describe how females can be more selective and how males can adapt.

Answer 16

Females in higher social rank are more mobile and can find resources more easily, therefore they can be selective in mate choice
Males can adapt by sharing the costs of reproduction or displaying appealing ‘qualities’

Question 17

Which two factors are men and women both sensitive to in mate choice?

Answer 17

MHC olfactory cues

Facial symmetry

Question 18

How do MHC olfactory cues describe mate fitness?

Answer 18

MHC is part of the immune system, it affects how you smell
Diverse offspring immune system is desirable
Human will prefer the smell of someone with different MHC to themselves

Question 19

How does facial symmetry describe mate fitness?

Answer 19

Low facial symmetry is related to:
Adverse foetal development conditions
Increased parasitic load
Increased homozygosity
Old age
Therefore, symmetrical faces are perceived to be more attractive

Question 20

Use two theories to explain why many of the sexually selected traits are seen in males rather than females

Answer 20

Bateman’s principle: female reproductive success is limited by resources, male reproductive success is limited by females

Parental investment theory: females reproductive costs are higher than in males, so they are more selective of male mates, therefore there is stronger selection in males

Question 21

Give examples of male mate preferences

Answer 21

Fidelity (due to paternity uncertainty)
Physical fertility cues:, youthfulness – less likely to miscarriage, feminine, neotenous faces, low waist-hip ratio of 0.7 (hourglass figure)

Question 22

Give examples of female mate preferences

Answer 22

Good genes: muscularity, height

Good dads, resources – high status, wealth, personality – low aggression, reliable, intelligent

Question 23

Male trade-offs

Answer 23

Males shift towards investing in parenting effort over mating effort in order to increase their reproductive success and paternity certainty

Question 24

Female trade-offs

Answer 24

In the short term, females place higher value on physical attractiveness and high masculinity
In the long term, females place higher value on good potential father, professional success, and low masculinity

Question 25

Are mate preferences universal?

Answer 25

David Buss’s mate choice study covered only 37 societies and so isn’t reliable

Question 26

What are the 3 statistics that David Buss’s mate choice study revealed?

Answer 26

In 92% of societies, men value physical attributes more than women
In 97% of societies, women value earning potential more than men
In 78% societies, women value ambition and industriousness more than men

Question 27

How does BMI preference vary cross-culturally?

Answer 27

In low resource areas higher BMI is preferred, because low BMI = lower fertility, lower SES, higher morbidity

In high-resource areas lower BMI is preferred, because high BMI = lower fertility, lower SES, higher morbidity

Question 28

Give one example of where mate preference changed depending on the environment

Answer 28

When Zulu men moved to the UK, their BMI preference fell.

UK born men with Zulu parents have the same BMI preference as the rest of the UK (Tovee et al., 2006)

Question 29

Give four different cross-cultural ways of signalling mate quality

Answer 29

Tattooing
Ritual of jumping over cows
Chinese foot-binding
Vanuatu land diving