Lecture 6 - Mate Choice and Sexual Selection

Question 1

During mating season what happens to female mallards?

Answer 1

They lose the feathers around their head from male aggression

Question 2

What do female praying mantis do after mating?

Answer 2

Eat their mate as the male won’t provide any service so gain their nutrient instead

Question 3

What are the two male mating strategies?

Answer 3

Elaborate courtship and sneaky-mating

Question 4

What is the trade-off for female guppys?

Answer 4

Accept the cost of being with the predators as males can’t follow them due to their bright colours. They do this to escape the continuous harassment from males

Question 5

What is anisogamy?

Answer 5

Reproduction between two gametes which differ in size and form

Question 6

Example of anisogamy

Answer 6

Male pigs have between 20 to 60 billion sperm
Female pigs have less that 20 eggs every cycle
- Females reproductive success is reduces due to her resources as only one large gamete
- Males invest large numbers to invest in getting as many offsprings with females as possible

Question 7

Why do females make life time investments in offspring?

Answer 7

Males can reproduce and have multiple offspring every year - women can only have one

Question 8

Explain how sexual conflict can drive an arms race

Answer 8

Reproductive strategies of males and females are no aligned
- Males can maximise success by mating with as many females as possible

Question 9

How do males maximise reproductive success?

Answer 9

By amount of females they mate with
- males mate with females they have never seen before

Question 10

How do females maximise reproductive success?

Answer 10

Females aim for quality
- brightly coloured display suggests quality of male and what foods they eat

Question 11

When is monogamy favoured?

Answer 11

1. Input from both parents is needed to raise offspring
2. Male has to guard mate to ensure he is father of offspring
3. Low change of meeting many females

Question 12

Example of monogamy when input from both parents is needed to raise offspring

Answer 12

Djungarian hamster males help keep their female and litter warm
- Pups survival decreases when males leaves the group

Question 13

Example of monogamy when male has to guard mate to ensure he is father of offspring

Answer 13

House sparrow males

Question 14

Example of monogamy when there is a low chance of meeting many females

Answer 14

Harlequin shrimp
- Once male has found female is is best for him to stay with female and maximise reproduction with her rather than leave and maybe not find another

Question 15

What are the two kinds of sexual selection?

Answer 15

Intersexual and intrasexual

Question 16

What is intersexual selection?

Answer 16

One biological sex choose mates of the other sex to mate with

Question 17

What is intrasexual selection?

Answer 17

compete with members of the same sex for access to members of the opposite sex

Question 18

Why does sexual selection occur?

Answer 18

Because of conflict over reproductive investment

Question 19

What is polygyny?

Answer 19

When males have more than one partner and females only have one

Question 20

What is an example of polygyny?

Answer 20

Killer wales

Question 21

What does polygyny promote?

Answer 21

Conflict between males and choosiness by females

Question 22

How does polygyny promote conflict between males?

Answer 22

1. Males fight to establish dominance → access to females
2. Dominance correlated with mating success
3. For control of resources that females require
4. For direct control of groups of females
5. Male-male conflict favours large, well-armed males

Question 23

Example of choosiness by females in polygyny?

Answer 23

Guppys - female choice and sexual selection on male traits
- Females choice favours elaborate male behaviour or morphology

Question 24

Polygyny is favoured when…

Answer 24

1. One sex is operationally rare
2. Males can control resources or females
3. Females can exert free choice

Question 25

What is polyandyry?

Answer 25

When females have more than one partner and males only have one

Question 26

Example of polyandry

Answer 26

Sandpipers

Question 27

How do female sandpipers behave like males?

Answer 27

Polyandry 1. Larger than males 2. Arrive at breeding grounds first 3. Fight for territories 4. Attracts several males to her territory 5. Skewed reproductive success

Question 28

When is polyandry favoured?

Answer 28

1. Females can escape parental care duties 2. Females require resources provided by >1 male 3. Males biased sex ratio

Question 29

What is poydynandry?

Answer 29

When females and males both have more than one partner

Question 30

Example of polygynandry

Answer 30

Barbary macaque - Females solicit copulation from several males and each male mates with several females

Question 31

What is the benefits of polygynandry?

Answer 31

1. Male gains several females 2. Males unable to defend female exclusively 3. Females gain access to wide range of resources 4. Females confuse males over paternity = increased paternal care, decreased infanticide 5. Females gain access to many males and genetic benefits

Question 32

When is polygynandry favoured?

Answer 32

When males can't monopolise females and females gain from multiple matings

Question 33

What does the decision of monogamy or polygyny in females depend on?

Answer 33

Availability of resources and habitats

Question 34

Why bother choosing what mating option?

Answer 34

Cost in energy and predation

Question 35

What are the benefits in choosing how many partners to have?

Answer 35

**Direct** Female HERSELF gains benefit and so lives longer or produces more offspring - Territory - Nuptial food - Paternal care - Reduced harassment **Indirect** Female’ OFFSPRING gain benefit and so lives longer or produces more offspring (more attractive?)

Question 36

How does the female know what benefits are available?

Answer 36

- Male traits signalling direct benefits - In some matings, a females only gets sperm

Question 37

Choosy females should...

Answer 37

- Pay attention to signals of available benefits - Prefer males with exaggerated signals - Prefer signals that males cannot “fake” - Maximise their benefits

Question 38

Example of runaway selection

Answer 38

Fisherian runaway - Female (trait) choice is established and male traits become more exaggerated. - Daughters of successful pairings will chose a mate using the same preferences as their mother - Sons of a successful mating will possess the same features as their father. - A trait becomes fixed in the population when all females chose it and when all males carry it.