Mating Systems

Question 1

Key mating systems

Answer 1

Monogamy
Polygamy
Polyandry (many males)
Polygyny (many females)
Promiscuity

Question 2

What affects mating systems? (4)

Answer 2

Differential investment of sexes
Ecological factors
Certainty of paternity
Dependence of young/impact of care

Question 3

Differential investment?

Answer 3

Sex that invests more will have fewer offspring; often females so polygyny is favoured

Question 4

Benefits for either sex in each mating system?

Answer 4

Females always benefit more from polyandry
Males benefit from polyandry in poor conditions, monogamy as conditions improve and polygyny in the best environments as female care alone is sufficient

Question 5

Ecological factors?

Answer 5

If resources are available equally, monogamy is favoured.

If there is inequality or high predation risk, males can hoard resources or defences and skew system to polygamy

Question 6

Mating systems and paternal certainty?

Answer 6

Uncertainty - polygyny

Certainty e.g. via mate guarding - monogamy

Question 7

Dependence of young

Answer 7

Altricial young are highly dependent and so males must invest = monogamy

Question 8

What contributed to the evolution of polygyny? (4)

Answer 8

Female defence
Resource defence
Scramble competition
Lekking

Question 9

Female defence?

Answer 9

Males defend regions where females aggregate, monopolising access to them

Question 10

Resource defence? with example

Answer 10

Males defend valuable territories, so females aggregate here e.g. cichlids collect empty shells in which females then lay their eggs

Question 11

Scramble competition?

Answer 11

Females/resources not always defendable e.g. dispersed population, too many females
Males attempt to find as many mates as possible

Question 12

Lekking?

Answer 12

Play behaviour e.g. males aggregate to perform mating dances or displays - females pick the best from these, but gain no resources

Question 13

Hypotheses for lekking? (3)

Answer 13

Hotspot hypothesis
Hotshot hypothesis
Female preference

Question 14

Hotspot hypothesis for lekking?

Answer 14

Males cluster where females are found, e.g. different bird species in Costa Rica move to one location for this

Question 15

Hotshot hypothesis for lekking?

Answer 15

Males gather around dominant others to increase mating chances, as less likely to encounter females alone.
Removing dominant males causes dispersal of subordinates

Question 16

Female preference argument for lekking?

Answer 16

Females only available at certain locations and so males have no choice but to congregate

Question 17

Distribution of monogamy?

Answer 17

Relatively rare in mammals (3%) fish (1%) but common in birds (90%)

Question 18

Why is monogamy strange?

Answer 18

Females invest much more than males - males do not seem to have a large pressure to do the same

Question 19

Hypotheses for monogamy? (3)

Answer 19

Mate guarding
Mate assistance
Female-enforced monogamy

Question 20

Mate guarding in monogamy?

Answer 20

If females rapidly mate with one male after another, it is adaptive for the male to stay and prevent this as they may not be able to find another female

Question 21

Mate assistance in monogamy?

Answer 21

If parental care substantially improves offspring survival e.g. for altricial species

Question 22

Female-enforced monogamy?

Answer 22

Females control access to other females e.g. burying beetle, where female pheromones deter males from recruiting other females to lay eggs

Question 23

What is social monogamy?

Answer 23

Often seen in birds - ‘couples’ form where duos spend most of their time together, raising offspring. Likely to be more even parental care due to egg-laying

Question 24

Promiscuity in birds?

Answer 24

Despite social monogamy females perform extra-pair copulations to obtain both parental care and the best possible genes