Lecture 10: Sexual selection

Question 1

investment into sexual selection traits are

Answer 1

costly, so should be naturally selected against

Question 2

natural selection vs sexual selection: Marine Iguanas

Answer 2

• large body size of males cant be explained by natural selection
• m & F have different body sizes (dimorphic) but both eat same
• size not for fitness
• SS explains these traits

Question 3

how did sexual selection originate?

Answer 3

• first sexual reproduction was between single celled organisms who produced gametes of equal size (isogamy)
• then origin of mating types, first step in differentiation of species (not being able to mate with own form)
• evolution of mating types can lead to
  1) ever increasing no. of mating types
  2) reduction to just 2

Question 4

ever increasing number of mating types example

Answer 4

in Ciliates, many spp have over 40 mating types (sex doesnt require just two)

Question 5

reduction to just two mating types was necessary for

Answer 5

ANISOGAMY (individuals producing different gametes)

Question 6

anisogamy:

Answer 6

individuals producing different gametes, the prevalent system we see across multicellular organisms today
-crucial step to SS

Question 7

Evolution of anisogamy:

Answer 7

• begin with a primitive isogamous sexual species
• imagine viability of zygote increases with size
• favours both SMALL (can produce more zygotes, greater chance of encountering and fusing with another gamete) and LARGE high fitness of resulting zygote.
• MEDIUM are mediocre
• • leads to DISRUPTIVE selection, v small and v large

Question 8

large gamete =

Answer 8

EGG, provides resources for embryo

Question 9

egg producers =

Answer 9

females

Question 10

sperm producers =

Answer 10

males

Question 11

SS really exists because of

Answer 11

• anisogamy, F produce few large gametes
• males essentially parasitise the parental investment of females
• M mating success usually increases linearly with number of mates, FEMALES DONT
• Male mating succes is more viable than females (BATEMAN PRINCIPLE)
• Variance leads to competition between males and choosiness of females (TRIVERS 1972)

Question 12

Sexual selection, who competes for who?

Answer 12

the sex investing least (usually males) competes for the sex investing most (usually females), and the sex investing most is choosy

Question 13

2 types of sexual selection

Answer 13

• Intra-sexual (within same sex)

- inter-sexual (between different sexes)

Question 14

how did sexually selected traits initially evolve?

Answer 14

Good genes or sensory exploitation?

Question 15

Good genes model:

Answer 15

• traits reflect the quality of the male, high quality males produce high quality traits
• females choosing a bright/large trait end up with a high quality male

Question 16

sensory exploitation model:

Answer 16

-Females have a pre-existing sensory bias for a bright or large ornament, a chance mutation in a male produces an ornament that matches this bias

Question 17

good genes: T+P

Answer 17

trait –> preference

Question 18

sensory exploitation: T+P

Answer 18

Preference -> trait

Question 19

example of sexual trait: sexual exploitation

Answer 19

Jones&hunter 1998

• auklets
• crested auklets were more favourable to females than least auklets
• -> preference evolved before trait so the trait originated sensory exploitation

Question 20

sexual selection results from ___, which generates ____ in offspring

Answer 20

anisogamy,

differentail parental investment