Lecture 9: Mating Systems

Question 1

Define ‘mating system’.

Answer 1

General behaviour strategy, or suit of behaviours and adaptations, employed in obtaining mates.

Question 2

What limits a males reproductive success?

Answer 2

Availability of females.

Question 3

What limits a females reproductive success?

Answer 3

• Their own fecundity

- Availability of resources.

Question 4

What determines the intensity of sexual selection?

Answer 4

The variance in fitness (greater in males).

Question 5

What equation can we use to determine the intensity of sexual selection?

Answer 5

Operational Sex Ratio (OSR) = No of receptive females/ No of sexually active males.

Question 6

Define ‘spatial distribution’.

Answer 6

Organisms live in a clumped, patchy distribution.

Question 7

Define ‘temporal distribution’.

Answer 7

Organisms live evenly spaced apart.

Question 8

What is the relationship between opportunity for sexual selection and mean female spatial crowding?

Answer 8

Positive.

Question 9

What is the relationship between opportunity for sexual selection and mean female temporal crowding?

Answer 9

Negative.

Question 10

What is the Emlen and Oring Hypothesis?

Answer 10

Like competition for scare resources, male reproduction is limited by the spatial and temporal availability of sexually receptive females.

Question 11

How can males increase their reproductive success?

Answer 11

• Increase number of mates

- Increase number of offspring they sire per mate.

Question 12

How can females increase their reproductive success?

Answer 12

Increase their own fecundity (i.e. number of offspring per clutch and clutch numbers).

Question 13

What is the Parental Investment (Triver’s) Hypothesis?

Answer 13

Sexual selection may be due to anisogamy (i.e. the size of gametes and the difference between the energy that goes into the gametes of the two sexes).

Question 14

Define ‘polyandry’.

Answer 14

Males mate once; females are variable in mating numbers.

Question 15

What are the costs of polyandry?

Answer 15

• Physiological harm
• Increased risk disease
• Increased predation risk
• Reduction in parental care.

Question 16

What are the direct benefits of polyandry?

Answer 16

• Nupital gifts (e.g. nursery web spider)
• Fertility assurance (one male mate may be infertile)
• Increased parental care
• Convenience polyandry (submission to avoid harm).

Question 17

What are the indirect benefits of polyandry?

Answer 17

• Trading up (females re-mate with partners of better quality)
• Genetic diversity (account for future environmental change)
• Good sperm (females re-mate with males with superior fertilising sperm which reflects male genetic quality)
• Sexy sperm (females re-mate with males to promote increased fertilisation efficiency arising from sperm competition)
• Genetic compatibility/ Inbreeding avoidance (females multiply mates to increase heterozygosity and avoid inbreeding).

Question 18

Give examples of male adaptations for avoidance and engagement in sperm competition.

Answer 18

• Pre and post-copulatory guarding
• Biochemical barriers to remating
• Physical barriers to female re mating (mating plugs)
• Traumatic insemination (bed bugs)
• Sperm morphology and function
• Testes size and sperm production
• Copula duration
• Copulation frequency.

Question 19

Define ‘monogamy’.

Answer 19

Each sex mates only once.

Question 20

Define ‘polygyny’.

Answer 20

Females mate once; mates are variable in mate numbers.

Question 21

Define ‘polygamy’.

Answer 21

Both sexes have variable mate numbers. Male mating success is approx = female mating success.

Question 22

Define ‘polyandrogyny’.

Answer 22

Both sexes have variable mate numbers; female mating success is more variable than male mating success.

Question 23

Give examples of monogamous species.

Answer 23

• Black-browed albatross

- Prairie vole.

Question 24

What are the predictions of monogamy?

Answer 24

• Rare
• No or low opportunity for sexual selection
• Negligible sexual dimorphism
• No sperm competition
• No sexual conflict
• Male parental care.

Question 25

Define ‘resource defence polygyny’.

Answer 25

Males defend resources essential to females. If males can monopolise the resources they can monopolise the females.

Question 26

Define ‘female (harem) defence polygyny’.

Answer 26

Females are gregarious for some reasons, not necessarily related to reproduction. Males control access to females directly.

Question 27

Define ‘seasonal harem’.

Answer 27

Males defend females during a particular time of the year e.g. sea lions.

Question 28

What are the predictions of polygyny?

Answer 28

• High opportunity for sexual selection in males
• Sexual dimorphism: weaponry for aggression and fighting
• No sperm competition
• Sexual conflict
• No male parental care.

Question 29

Define ‘leks’.

Answer 29

An example of polygamy with strong sexual selection e.g. black grouse, fallow deer.

Question 30

What are the predictions of leks?

Answer 30

• Very strong sexual selection in males (the lek paradox)
• Sexual dimorphism: male displays to attract female, weaponry, sperm competition adaptations
• Sexual conflict
• No male parental care.

Question 31

What are the predictions of polyandry/polyandrogyny?

Answer 31

• Strong sexual selection in females
• Sexual dimorphism: females aggressive, larger and possible weaponry
• Sexual conflict: females exploit males
• Sperm competition: possible but unlikely
• Male parental care.