L3 - Sexual Selection

Question 1

What are the two sub-categories of sexual selection?

Answer 1

Pre-copulatory (before mating)
Post-copulatory (after mating)

Question 2

What are the two types of pre-copulatory sexual selection?

Answer 2

Intra-sexual selection = same sex competition
Inter-sexual selection = mate choice

Question 3

What are the two types of post-copulatory sexual selection?

Answer 3

Sperm competition = same sex competition
Cryptic female choice = mate choice

Question 4

Why do males compete for females?

Answer 4

Their fitness increases the number of females they mate with

Question 5

Why are females so selective with the males they mate with?

Answer 5

Their fitness is increased with the quality of their mate

Question 6

How do the production costs of gametes differ between sexes?

Answer 6

Much higher for females - eggs much larger than sperm (can be 20% of body mass)

Question 7

What leads to competition between males, and females choosing between males?

Answer 7

Because males gain more than females by multiple matings

Question 8

What does sexual selection and natural selection interact to produce?

Answer 8

Trait distributions

Question 9

How does intra-sexual and inter-sexual selection show in behaviour?

Answer 9

Intra-sexual = out compete rivals
Inter- sexual = be more attractive

Question 10

What percentage of male California elephant seals father 85% of pups?

Answer 10

4%

Question 11

What is sexual weaponry?

Answer 11

Weaponry that is used to fight off competition for mates, usually males fighting/ competing for females

Question 12

Give two examples of the cost of sexual weaponry:

Answer 12

(Emlen 2000) - developmental cost in beetles, trade off between horn size and eye size
(Johnston et al,. 2013) - shorter lifespan in Soay sheep, larger horns increase reproductive success but reduce survival

Question 13

Give two examples of pre-copulatory sexual selection

Answer 13

Courtship displays
Elaborate architecture

Question 14

Give two examples of pre-copulatory sexual selection which have a direct benefit

Answer 14

Oral gifts - nutrients to consume e.g Great Grey Shrike (aka Butcher bird)
Seminal gifts - protein rich ejaculate to nourish female e.g bush crickets

Question 15

What is the “sexy son hypothesis”?

Answer 15

Females choose males based on producing offspring with the best chance of reproducing

Question 16

What is Zahavi’s Handicap principle?

Answer 16

Females choose males because he was able to survive with a costly sexual trait (assumes sexual signals are costly – ‘honest signals’)

Question 17

What is runaway sexual selection?

Answer 17

When the choosing sex (usually female) prefer a version of a trait, despite the fitness cost of that version. The trait originally gave a survival advantage but now it is too extreme e.g peacock tails

Question 18

What experiment did Malte Andersson (1982, 1992) carry out which showed runaway sexual selection?

Answer 18

Experimented on long-tailed widow birds, artificially manipulated tail length by cutting and sticking feather
Results showed males with elongated tails had more active nests

Question 19

What is sperm competition?

Answer 19

Competition between sperm from rival males to fertilise a female’s egg(s), extended form of male-male competition

Question 20

What are ways in which males reduce their risk of sperm competition?

Answer 20

• Mate guarding
• Removing rival male sperm during mating (Odonata have complex male genitalia which can remove rival sperm)
• Increase investment in sperm production

Question 21

For which animal, do testes make up the largest percentage of body volume? And what is that percentage?

Answer 21

Northern giant mouse lemur, 5.5%

Question 22

For which animal, do testes make up the largest percentage of body weight? And what is that percentage?

Answer 22

Tuberous bush cricket, 14%

Question 23

In primates, what does the size of the testes correlate with?

Answer 23

Whether it is a multi-male breeding system or not: if multi-male the testes are bigger
Similar effect seen in butterflies

Question 24

What increases in males when presented with a new female?

Answer 24

Sperm investment/ count

Question 25

How can females still be in control of which male fertilises her eggs after mating?

Answer 25

In some species, females are able to use physical or chemical mechanisms to control a male’s success in inseminating her eggs
E.g in red jungle fowl, females eject more sperm after mating with subordinate males