Lecture 10 - sexual selection

Question 1

What is a rule for evolution?

Answer 1

• selection acts on replicators
• these are individual units that replicate themselves
• those that leave most copies are the most successful

(species & individuals aren’t replicators)

Question 2

What are the ingredients for natural selection & competition?

Answer 2

• ecological competition is the consequence of limited amounts of resources
• resources can include food, water, shelter, space or mates
• there is a direct relationship between amount of resource captured & fitness

Question 3

What is sexual selection?

Answer 3

• intrasexual selection
• intersexual selection

Question 4

What is fecundity?

Answer 4

the amount of offspring

Question 5

What is fertility?

Answer 5

the amount of gametes

Question 6

What does sexual selection lead to?

Answer 6

different adaption

Question 7

What is sexual dimorphism?

Answer 7

• male & female
• they have different adaptions - e.g. male has claws to fight off predators
• sexual selection produces differences between the sexes

Question 8

What are mating systems?

Answer 8

competitions for mates had led to diversity of outcomes in terms of mating systems

Question 9

What is monogamy?

Answer 9

1 male & 1 female - one partner, little sexual selection - no sexual dimorphism

Question 10

What is polygamy?

Answer 10

male & females have multiple partners

Question 11

What is polyandry?

Answer 11

females has multiple partners

Question 12

What is polygyny?

Answer 12

male has multiple partners

Question 13

What is the extra-pair paternity?

Answer 13

• discovered in 1990s with advent of genetic fingerprinting
• surprising high rates in supposedly monogamous species

Question 14

How is Dunnock an example of extra-pair paternity?

Answer 14

• very variable mating systems
• frequently polyandrous, despite appearing monogamous
• however females frequently mate with unpaired males (sneak)
• mates 100 times a day
• important consequences

Question 15

Describe extra pair paternity statistics

Answer 15

• chaffinch 17%
• blue tit 10-15%
• dunnock 0-36%
• tree swallow 38-76%
• superb fairy wren 75-85%

Question 16

What are the characteristics of polygamy, polyandry & polygyny?

Answer 16

• multiple partners optimal
• sexual selection
• sexual dimorphism

Question 17

What is intrasexual competition?

Answer 17

• in polygamous mating systems, there are a few winners and lot of losers –> intense competition for mates
• competition between members of the same sex is called intrasexual selection
• thus had led to the evolution of several behaviours as a consequence

Question 18

What are examples of behaviours carried out due to intrasexual competiton?

Answer 18

• male-male competition - fighting
• mate guarding - pre-copulatory & post-copulatory
• sperm competition - direct competition between sperm (led to adaptions in sperm - e.g. being motile)

Question 19

What is ‘lek competition’?

Answer 19

• a gathering of males that compete with each other
• they display with others and females observe the lek
• the females choose the ‘best males’
• lemming is costly for males
• may be less costly for females
• example (red grouse)

Question 20

What is intersexual selection?

Answer 20

• females choose mates
• in lek species, females choose one male
• other species, males display to females
• typically in polygynous mating systems (females mate with one male)
• but reverse can happen - polyandrous mating system

Females choose males based on their characteristics

Question 21

What do females gain from intersexual selection?

Answer 21

1. Access to resources
2. Access to good genes - utilitarian
3. Access to good genes - attractiveness

Question 22

What access to resources do females gain?

Answer 22

e.g. courtship feeding

Question 23

What access to good genes (utilitarian) do females gain?

Answer 23

• females choose genes that confer high survival to offspring - resistance to parasites

Question 24

What access to good genes (attractiveness) do females gain?

Answer 24

• females choose attractiveness genes that make male offspring more attractive to females

Question 25

What is runaway sexual selection?

Answer 25

Anderson (1982):
- experimentally altered tail length of males

• reduced tail = lower mating success
• increased tail = more mating success

Question 26

How are peacocks an example of runaway sexual selection?

Answer 26

female preference for long tail leads to selection for long tailed males - this loops

Question 27

Are natural selection & sexual selection operating in the same direction?

Answer 27

not always

Question 28

How is Endlers an example of sexual vs natural selection?

Answer 28

• Endler: course vs fine gravel selection
• if predator present - natural selection (favours fish that fit into background)
• if predator isn’t present - sexual selection (favours fish that look different from their background)

Question 29

What is comparative evidence?

Answer 29

look at patterns across multiple species to see whether traits vary as we would predict

Question 30

What is the prediction regarding sexual vs natural selection?

Answer 30

• in species that experience stronger natural, sexual selection should be weaker.
• strength of sexual selection is correlate with sexual dimorphism, i.e. males are more different from females when sexual selection is stronger
• e.g. predation pressure - species in habitats that are prone to predation should have less dimorphism

Question 31

What predation risk is associated with off-ground nesting?

Answer 31

less predation risk

Question 32

What predation risk is associated with ground-nesting?

Answer 32

more predation risk

Question 33

What is runaway sexual selection?

Answer 33

• exaggerated traits can evolve through sexual selection
• however, as selection proceeds, genetic variation becomes used up
• in the extreme, in a strongly selected population, variations between individuals are not due to genetics but random (additive genetic variation is low)
• although this is expected, the reverse is actually observed
• sexually selected traits have high variability & additive variance
• The Lek Paradox