week 5+6 - mating systems

Question 1

Polyandry

Answer 1

for a male
- share one female

for a female
- sole access to several males

e.g. 2 males, 1 female

Question 2

monogamy

Answer 2

for a male
- sole access to one female

for a female
- sole access to one male

Question 3

polygynandry

Answer 3

for a male
- share several females

for a female
- share several males

Question 4

Polygyny

Answer 4

for a male
- sole access to several females

for a female
- share one male

e.g. 1 male and 2 females

Question 5

Polyandry
description

Answer 5

• Female ensures reproductive success, but it is relatively rare in mammals and birds. It is most commonly found in insects (e.g. eusocial species such as bees and termites) and reptiles (e.g. tortoises).

Question 6

polyandry
genetic benefits

Answer 6

genetic benefits

1. fertility insurance hypothesis
   - multiple males reduces risk that some eggs will remain unfertilised
2. good genes hypothesis
   - social partner lower genetic quality than other potential donors
3. genetic compatibility hypothesis
   - multiple males increases amount of sperm avaliable
   - increases chance that some will have DNA that is a good match

Question 7

polyandry
material benefits

Answer 7

1. more resources hypothesis
   - more males means more resources or parental care
2. better protection hypothesis
   - more time with mates/protectors stops other males harassing them
3. infanticide reduction hypothesis
   - confusion over paternity

Question 8

polyandry
case study

Answer 8

Case Study: Marmosets (Callitrichids)! Marmosets have a dominant breeding female(s) and several males and subordinate females. Dominant females may suppress ovulation in subordinate females. The dominant female usually gives birth to twins every six months but the males take over the majority of the childcare after a short period of time. All males will help as they are unsure who the Father is.

Question 9

monogamy
description

Answer 9

• Both parents contribute to parental care (making the wrong choice has high risks!).
• Most commonly used strategy in birds.

Question 10

monogamy
benefits

Answer 10

shared care, territory maintenance and resources.

Question 11

monogamy
disadvantages

Answer 11

reduced genetic variation in your offspring (this does lead to sneaky extra-pair copulations where females will mate with males outside of the monogamous pair).

Question 12

monogamy
case study

Answer 12

Case Study: French Angel Fish (Pomacanthus paru). They live, travel and hunt in pairs. They mate for a lifetime, are strongly territorial and show no sexual dimorphism. Some will remain solitary even after their mate dies :-(

Question 13

polygynandry
description

Answer 13

• Looser bonds between males and females, rarely pair bonded but there may be an element of choice.
• Males may care for broods of multiple females e.g. lions and bonobos.
• Strategy is more likely when the environment is unpredictable (always guaranteed a mate).

Question 14

polygynandry
case study

Answer 14

Case study: Red foxes (Vulpes vulpes). Were thought to exist only in monogamous pairs, but a study in Bristol in 2003 found more more mixing and mating between individuals than was expected. 54% of pairs were socially monogamous, but females were found to sire cubs with multiple fathers in 38% of litters. On average 1.6 males sired a single litter and in one instance a single litter had 7 fathers!

Question 15

polygyny
description

Answer 15

• This system is often used by males to increase reproductive fitness.
• Most commonly seen in mammals and there are three main types

Question 16

polygyny
3 main types

Answer 16

Resource Defence Polygyny: As discussed in the introduction, this is where females are attracted to a resource, males compete to control that resource and thus a successful male gains priority access to the females. The fittest males generally hold the best territories. This often occurs in species where the resources are patchy (and thus can be controlled) e.g. Topi antelope (Damaliscus korrigum).
Harems: This is where a defended group of females associate with one male. The females may be related and males compete to gain access to a group. Females within the group often have their own dominance hierarchy. The larger a harem, the lower the offspring mortality as there are more individuals to look out for predators etc. Common example are gorillas who are not resource limited.
Leks: A lek is a temporary aggregation of males looking to attract a mate (unlike the cases above which occur over a longer period of time). Leks do not form in relation to resources, rather than occur in an area where females may need to travel through. They occur in cases where males cannot monopolise either the resources or the females themselves. Within a lek males may perform displays and compete with one another to get the best position. The closer to the centre of the lekking arena the better the male is considered to be and the more females will likely choose him, thus the central male with have many females. An example is in Black grouse (Tetrao tetrix).

Question 17

group living
advantages

Answer 17

less energy

choice

more than one partner

assess mate quality over a longer period

mate sampling

Question 18

group living
disadvantages

Answer 18

male-male competition

extra pair copulations

less chance for subordinates

restriction and control by dominants

risks of inbreeding