2: Sexual selection

Question 1

Define isogamy

Answer 1

= same size gametes (ancestral sexual state)
so any 2 gametes can fuse to form a zygote

Question 2

Whats the problem with isogamy?

Answer 2

Can accidentally fertilise your own gametes → waste of resources and time

Question 3

Why is 2 the most common number of mating types?

Answer 3

• More mating types means more opportunities to mate
• 2 types means you are limited to 50% of pop. rather than like 75% (4 types)
• Might be simplest to have 1 donor type and one receiver type → could be unstable if there are lots of different types
• Might not be needed: if pop. is big enough and you live reasonably long you will meet the other mating type

Question 4

Each individual has a fixed energy budget for gamete production, so it can make…

Answer 4

Large = high fitness of resulting zygote

OR

Small = can produce more, so more chance of encountering & fusing with another gamete

Question 5

Given that gamete production is costly, why do organisms not make a meduim sized gamete? (rather than small/large)

Answer 5

Because medium sized gametes are mediocre at both functions
= Disruptive selection on gamete size

Question 6

Define Anisogamy

Answer 6

Union of 2 gametes that differ in size/form
e.g sperm and egg

= Differential gametes investment
= Differential parental investment

Question 7

Describe how anisogamy sets up the potential for sexual selection

Answer 7

• Male mating success usually increases linearly with no. of mates
• Low fitness cost for males if they mate with a ‘sub-par’ female
  = Selects for male promiscuity
• Females don’t benefit as much from increasing no. of mates
• High cost if she mates with a sub-par male
  = selects for careful female mate choice

Question 8

Define Bateman’s Principle

Answer 8

male mating success is more variable than female mating success

Question 9

Define Parental Investment Theory

Answer 9

Variance leads to competition between males and choosiness among females

Question 10

Describe the direct benefit in female choice

Answer 10

Direct fitness increase, choose male that will directly provide resources to female and her offspring

Question 11

Define Fecundity

Answer 11

potential number of offspring that could be produced
Good parenting ability

Question 12

Describe the Indirect benefit of female mate choice

Answer 12

genetic benefit, choose the male that will provide genes to make fitter offspring

Question 13

Describe the Fisherian runaway sexual selection model

Answer 13

Positive frequency dependence
= runaway selection where trait becomes more and more common and more exaggerated

Question 14

Describe the Good genes model

Answer 14

• Only males with ‘good genes’ can afford to invest in the trait
  = honest signal of genetic quality
• we’d predict that male traits should reflect offspring viability