Lecture 11: Sexual selection

Question 1

Intrasexual selection:

Answer 1

• WITHIN THE SAME SEX

- -> male vs male competition; selects traits like horns etc. & fighting

Question 2

Intersexual selection:

Answer 2

• BETWEEN SEXES (M&F)

- “attractiveness” traits - peacocks!

Question 3

Do natural selection and sexual selection always go hand in hand?

Answer 3

NO. e.g. stickle back male
During breeding season: blue eyes and red chest (This attracts unwanted attention i.e. from predators BUT also attracts mates.
non-breeding season plain

so selected for by sexual selection. selected against by natural selection

Question 4

Female =

Answer 4

eggs

Question 5

Male =

Answer 5

sperm

Question 6

a males fitness is determined by

Answer 6

successfully getting a mate, not by producing gametes (sperm)

Question 7

a female fitness is determined by

Answer 7

producing gametes (eggs) as she has a limited number of gametes (eggs)

Question 8

sexual dimorphism

Answer 8

‘sex 2 form’
the differences in appearance between males and females of the same species
often the male showing sexual selective traits
e.g. peacock/lions

Question 9

sex role reversal -

Answer 9

often driven by ecology

e. g. dotterel bird (scotland)
- male dotterel raises chicks
- female looks for more mates
- female is more brightly coloured than male

Question 10

monogamy

Answer 10

1 M & 1 F

• one partner optimal
• little sexual selection
• little sexual dimorphism
• e.g. termites

Question 11

polygamy

Answer 11

M & F can have >1 mate

• multiple partners optimal
• sexual selection
• sexual dimorphism

Question 12

polygyny

Answer 12

1 M & >1 F

-male bigger and more colourful

Question 13

polyandry

Answer 13

1 F & >1 M

-female bigger and more colourful

Question 14

Intrasexual competition:

Answer 14

• fighting
• male vs male rushing display
• mate guarding: post&pre mating
• sperm competition

Question 15

Intersexual competition:

Answer 15

PEACOCKS

Question 16

why should females choose one male or another?

Answer 16

1) access to good resources

2) getting good genes for their offspring

Question 17

Runaway sexual selection e.g.

Answer 17

Natural selection for long-tailed males –> sexual selection for female choice of long-tailed males –> REPEAT