Sexual Selection

Question 1

Who was the first to notice that one sex often has extravagant features?

Answer 1

Charles Darwin

Question 2

What is the fundamental difference between the sexes?

Answer 2

Gamete size

Question 3

What is isogamy?

Answer 3

Equal sized gametes meaning neither male or female forms- this occurs in many simple unicellular organisms

Question 4

What is anisogamous?

Answer 4

One of the gametes is large, immobile and food rich

The other gamete is small, immobile and essentially just a delivery mechanism for DNA

Question 5

Why is parental investment usually greater in females than males?

Answer 5

Males: best increase success by finding and fertilising many different females

Females: best increase reproductive success by increasing the rate of converting resources into egg and offspring

Question 6

What is intrasexual selection?

Answer 6

Competition between members of the same sex (usually males)

The female doesn’t have a choice

Question 7

What is intersexual selection?

Answer 7

Still competition between (usually) males but the females choose the winner

Question 8

Give an example of intrasexual selection

Answer 8

Elephant seals

The males are much larger and compete with each other to get all the matings in a harem

Question 9

Give an example of intersexual selection

Answer 9

Long tailed widow bird

The female selects the male based on their tail length

Andersson (1982) found the birds with elongated tails had significant increases in mating success

Question 10

In the bower bird what information is the female getting from the bower

Answer 10

An indicator of social status and sperm quality

Question 11

What is fisher’s hypothesis? (1930)

Answer 11

Females find certain traits attractive, therefore by mating with these attractive males females will have attractive offspring

Also known as the ‘sexy sons’ hypothesis

Question 12

What is runaway selection?

Answer 12

Where animals develop more and more extravagant traits

It will stop when it becomes too much of a handicap

Question 13

What is the handicap hypothesis?

Answer 13

Alternative to fisher’s hypothesis

Extravagant male features actually create a handicap and this handicap is why the females choose them because it is a good indicator of male quality

Must be good at surviving to do so with a handicap

Question 14

What did Hamilton and Zuk (1982) suggest about parasite resistance?

Answer 14

Sexual displays are good indicators of resistance to disease or parasites

Females will choose the ones resistant to disease/parasites

Question 15

What study supported Hamilton and Zuks theory?

Answer 15

Study on the three spined stickleback

Females chose the reddest males in white light as this was an indicator of fitness and less parasites

In green light there was no effect on choosiness

Question 16

How can sexual selection lead to behavioural isolation?

Answer 16

Runaway selection can drive reproductive isolation because females select for exaggerated characteristics, if this selection becomes strong enough it can cause behavioural isolation

This can be through courtship display differences etc.

Question 17

Give an example of behavioural isolation

Answer 17

Hawaiian drosophila

Two different head sizes (narrow or wide)

Found no difference in female choice over head size but there was a difference in mating displays which prevented mating from occurring

Question 18

What does the faster male theory suggest?

Answer 18

That male sterility is more common than females when bred with relatives due to spermatogenesis being more sensitive to change

Alternatively could be due to sexual selection/conflict causing increased divergence in male genetics

Question 19

What is sympatric speciation?

Answer 19

Species that share the same habitat but become reproductively isolated from each other

Question 20

What is allopatric speciation?

Answer 20

When species within the same population become geographically isolated