Mating effort and sexual selection, Lecture 10 & 11

Question 1

Natural selection

Answer 1

Causes the evolution of traits which enhance chances of survival.

Question 2

Why have some traits which seem to reduce survival evolved?

Answer 2

Darwin’s theory about this is sexual selection

Question 3

Sexual selection

Answer 3

Causes the evolution of traits which gives the owners a mating advantage over other of the same sex

Question 4

Secondary sexual characteristics

Answer 4

Traits which differ between the sexes

Question 5

Examples of secondary sexual characteristics

3

Answer 5

size dimorphism,
elaborate displays and colours
weapons - antlers, horns, etc.

Question 6

What aren’t secondary sexual characteristics connected with?

Answer 6

gamete production or transfer

Question 7

Why is it usually the males that compete?

2 reasons

Answer 7

1. gamete size

2. potential rate of reproduction

Question 8

Gamete size males

Answer 8

sperm,
very small,
large numbers ‘cheap’

Question 9

Gamete size females

Answer 9

eggs,
large,
small numbers ‘expensive’

Question 10

Investment per gamete in females is …

Answer 10

relatively high

Question 11

Potential rate of reproduction

Answer 11

higher in males than females

Question 12

Bateman’s experiment

Answer 12

drosophila, mating and success

Question 13

What limits mating in males

according to Bateman’s experiments

Answer 13

access to females

Question 14

What limits mating in females

according to Bateman’s experiments

Answer 14

egg production

Question 15

Ardent males and …

Answer 15

choosy females

Question 16

… and choosy females

Answer 16

ardent males

Question 17

The sex with the greater potential rate of reproduction competes whilst…

Answer 17

the other sex is choosy

Question 18

The advantages of being choosy

Answer 18

1. investment in eggs is relatively high
2. breeding opportunities relatively rare
3. needs to get:
   - right species
   - best quality male available

Question 19

Two types of sexual selection

Answer 19

intra and inter

Question 20

Intra-sexual selection

Answer 20

Competition for mates between individuals of same sex

Question 21

Inter-sexual selection

Answer 21

Mate choice

Question 22

Examples of use of secondary sexual characteristics in intra-sexual selection

Answer 22

weapons
size
signals

Question 23

Examples of secondary sexual characteristics in male ungulates

Answer 23

antlers and horns in males

none in females

Question 24

Types of ungulates

Answer 24

gazelle, 
moose,
deer (red),
ram, 
antelope,

Question 25

Were the evolution of antlers and horns in ungulates due to sexual selection or natural selection

Answer 25

sexual selection,

• not always used for defense
• many shed when predation risk is highest: in winter

Question 26

Example of intra-sexual selection: size

Answer 26

competitions often won by the largest male,
selects for larger than average size male,
which can lead to extremes of size dimorphism

Question 27

Example of intra-sexual selection: size dimorphisms in…

Answer 27

elephant seals

Question 28

Intra-sexual selection, rituals and displays

Answer 28

neither benefit from fighting,

‘sizing up’ rituals beneficial to both parties

Question 29

Example of Intra-sexual selection

rituals and displays

Answer 29

Red deer,
display increases in intensity,
1/roaring
2/ parallel walking
3/ fighting

Question 30

Rituals can lead to extravagant body parts

2 examples

Answer 30

1. peacock tails

2. stalk-eyed flies

Question 31

Three aspects of inter-sexual selection

Answer 31

1. getting the right species
2. direct benefits
3. indirect benefits

Question 32

Getting the right species

inter-sexual selection

Answer 32

hybrids often less fertile or less fit

Question 33

Direct benefits
(inter-sexual selection)

Answer 33

males may come with resources:

1. food
2. nests or laying sites
3. parental care
4. protection from harassment

Question 34

Indirect benefits
(inter-sexual selection)

Answer 34

males provide genetic benefits:

1. parasite resistance
2. longevity
3. ‘good genes’ - inherited by the offspring and increase their viability

Question 35

When is female preference greatest?

inter-sexual selection

Answer 35

when cost of error is greatest

Question 36

Overlap or hybrid zone

Answer 36

Areas where two species overlap and may produce hybrid offspring

Question 37

Are females from the hybrid zone more or less likely to go to the correct male?

Answer 37

more

Question 38

Are females basing their choice on secondary sexual characteristics?
example

Answer 38

Long-tailed widow bird,
males have very long tails but females don’t - suggests a role in mate choice
experiment: trapped males, changed tail length,
females preferred longer tailed so yes to question

Question 39

Sedge warbler song

Answer 39

females don’t sing,
males have a complex song which is made up of elements, more elements = larger repertoire,
males with larger repertoires pair early,
this could be related to other factors such as age,
song complexity may signal useful traits such as longevity

Question 40

Evolution of elaborate traits

2 main theories

Answer 40

1. Fisher’s runaway theory

2. good genes or handicap principle - Zahavi

Question 41

Fisher’s runaway theory about elaborate traits

Answer 41

females prefer for a trait becomes genetically linked with a trait

Question 42

Fisher’s runaway theory about elaborate traits

how can a preference arrive?

Answer 42

arbitrary - no cost or benefit

Question 43

Fisher’s runaway theory about elaborate traits

how does a preference become genetically linked to a trait?

Answer 43

natural selection to start with

Question 44

Fisher’s runaway theory about elaborate traits

how does genetic linking of a trait lead to runaway selection?

Answer 44

sensory bias,

eg: loud calls or obvious mating signals perceived first

Question 45

The handicap principle about elaborate traits

eg: with tails

Answer 45

long tails are expensive handicaps,
females prefer them because they signal an ability to survive despite the handicap,
may be a signal male viability (longevity, parasite load, etc.)