Lecture 11: Human and animal

Question 1

Define polygamy
Define polygyny
Define polyandry

Answer 1

Multiple partners
Multiple female partners
Multiple male partners

Question 2

How does polygyny work?

Answer 2

It starts off with a distribution of resources, followed by a distribution of females, then a distribution of males, resulting in a mating system. This happens with grey sided voles.

Question 3

What are the four types of polygyny

Answer 3

Female defense polygyny
Resource defense polygyny
Scramble competition polygyny
Lek polygyny

Question 4

Describe female defense polygyny

Answer 4

When female mammals are social, males aren’t ever monogamous. Males defend the females from invading males.

Question 5

Describe resource defence polygyny

Give 2 examples

Answer 5

When males defend a territory or resource that a female visits
Examples: Male antlered flies defend rotten logs which are for egg laying
African cichlid fish gather females’ eggs and steal them from other males.

Question 6

Describe scramble competition polygyny

Answer 6

These are also called explosive breeders. The females are only receptive for a few days, the males rush to mate with as many females as possible. The males aren’t territorial. Frogs are explosive breeders.

Question 7

Why do females agree to mate with more than one male?

Answer 7

Because it means they have increased territory quality

Question 8

Describe the polygyny threshold model

Answer 8

Pribil and Searcy did an experiment with Red-winged blackbirds. They removed some females and the polygynous females were predated more and as result, produced less offspring. This is the cost of ploygyny. The territories were then boosted and the females chose the better site even though it was polgynous. The benefit of the high quality nest outwighs the cost of polygyny.

Question 9

Describe lek polygyny

Answer 9

It comes from the word play and it’s relatively rare but is found in some mammals, birds, amphibians and insects. It involves the males gathering and displaying themselves to the females. The females are very choosy and the males aren’t involved with parental care at all. This means there is high variance in male reproductive success as some males will get picked more than others.

Question 10

What is the evolution of lekking?

Answer 10

It consists of three main hypotheses; the hotspot hypothesis, the hot shot hypothesis and the female preference hypothesis.

Question 11

Describe the hotspot hypothesis

Answer 11

It’s when males gather where females visit, however, male aggregation is usually to tight to follow female dispersion. Male harbour seals aggregate at underwater spots where females travel.

Question 12

Describe the hotshot hypothesis

Answer 12

When males cluster around highly attractive males to increase their chances. If the alpha males are removed the subordinates leave, however if a subordinate is removed, it’s just replace by another subordinate. This is found with marine iguanas.

Question 13

Describe the female preference hypothesis

Answer 13

Females are attracted to larger leks as they can find the best males there.

Question 14

Describe monogamy

Answer 14

It’s when a male and a female stay together and only have one partner. It’s rare in nature; only 3% of mammals are mongamous and 15% of primates, however, 90% of birds are monogamous. However, why would males accept monogamy as it wastes sperm? There are three hypotheses: Mate guarding, female enforced and mate assistance.

Question 15

Describe mate guarding

Answer 15

It prevents sperm competition which increases paternity certainty. It follows the operational sex ratio of sexually active males to sexually active females. The females are widely dispersed, receptive after mating and have a short fertile window. Clown shrimp mate guard. When there are non-overlapping female ranges then males are unable to monopolise more than one female. This is faculatative monogamy.

Question 16

Describe mate assistance

Answer 16

Males carry the eggs in a brood pouch but only carry a clutch at a time. Therefore, there is no advantage for the male to find another female. They fulfil their potential reproductive rate. Seahorses follow this hypothesis. So does the djungarian hamster, however, there isn’t a relationship between paternal care and monogamy in mammals. Starlings follow this as they help rear the offspring because the chicks require a lot of parental care in order to survive. This is obligate monogamy.

Question 17

Describe female enforced mongamy

Answer 17

The females don’t allow the male to mate with anyone else, e.g. jealous girlfriends. The burying beetle supports this, as does the yellow breasted chat.

Question 18

Describe the fidelity of birds

Answer 18

Birds were assumed to be highly mongamous, however, DNA profiling has said differently. 90% are socially mongamous but 10% are sexually monogamous. They have extra pair copulations. EPCs can be up to 35% in many species. Gibbs et al found that many of these EPCs happen in neighbouring nests and most of the males’ offspring are in different nests.

Question 19

Discuss divorce in swans

Answer 19

Rees et al found that only 25% of divorcing whooper swans had bred the previous year. 48% of non divorcing swans had bred. Maybe the females find a better alternative with increased dominance rank.

Question 20

Discuss the cost of mating

Answer 20

If the female is polyandrous, then this correlates to a higher immune system (primates), however, females are usually mongamous, meaning their immune system isn’t as strong. Sperm can damage female fruit flies and decrease their chance of survival.

Question 21

Discuss polyandry’s benefits and costs

Answer 21

It directly benefits male butterflies as the more mates they have, the more reproductive output they have. It also benefits them in terms of protection, langurs sometimes mate with multiple males to reduce the chance of infanticide. It’s good for females as they have the best opportunity to find the good genes.
However, polyandry isn’t beneficial for males as it means they have to share paternity and they will have missed opportunities for mating.

Question 22

Discuss good genes in terms of competition

Answer 22

Klappert 2007 found that females would improve their fitness via their sons. Therefore, they would pick the most attractive male to ensure that their sons would produce more grandchildren as they would be more successful.

Question 23

Discuss genetic compatibility of birds and their offspring that commit infidelity

Answer 23

The offspring produced via the EPCs had better immune responses whereas other offspring of these males had average immunity.

Question 24

Discuss sex role reversed species

Answer 24

Some species defy the normal pattern; the females compete, they’re ornamented and are aggressive and territorial, for example phalaropes. In some species, the males provide parental care; the females gain from additional matings and males have a slower potential reproductive rate, e.g. seahorses.

Question 25

What species is polyandrous, polygymous, monogamous and polygynadrous?
What gender does each benefit?
What is this called? Explain

Answer 25

Dunnocks and humans
Polygyny: Males
Monogamous: Average for both
Polyandrous: Females
A variable mating system, however there is a conflict of interest as different systems benefit different individuals. Terretorial male dunnocks usually have variable mating systems depending on whether they're alpha or beta males. This highlights the males' different competitive abilities and it alters the sex ratio, there is usally vegetation in the territory and the females usually encourage mixed paternity by mating with the less visited male.

Question 26

Do harem sizes correlate to size dimorphism in chimps?

Answer 26

Roughly, not a strong correlation

Question 27

What is polygyny associated with in humans?

Answer 27

Rainfall and pathogen load. It’s important to have a wide variety of male quality. 85% of humans are polygynous, many societies used to be more polygynous. However, Henrich found that the shift from polygyny to monogamy is associated with lower crime rates, less competition of young brides, increased gender equality and less child neglect. Although, it still varies.