Sexual selection (Meg)

Question 1

Name an example of a simultaneous hermaphrodite

Answer 1

leopard slug

Question 2

How do leopard slugs mate?

Answer 2

mating pairs hang from mucus thread while copulating- mate at night time

Question 3

Name an example of a sequential hermaphrodite

Answer 3

clown fish

Question 4

Name a species that reproduces almost entirely by self fertilisation

Answer 4

cactus

Question 5

How do bacteria like e-coli reproduce?

Answer 5

use conjugation and other mechanisms to exchange genetic material

Question 6

How do angler fish reproduce?

Answer 6

when a male finds a female, he bites + attaches himself permanently to her + his body fuses with hers + his organs largely degenerate except for his testes, which grow to fill most of his body- male contribution = gametes

Question 7

What is Darwins sexual selection hypothesis?

Answer 7

secondary sexual traits increase mating success

Question 8

Describe the method of an experimental test of darwins sexual selection hypothesis

Answer 8

METHOD = Male long-tailed widowbirds have extremely long tail feathers- these were artificially shortened in one group and lengthened in another
Mating success was measured by number of females nesting on each males territory
- 2 controls = no tail manipulation in one group of males + tails were cut then reattached in other group

Question 9

What were the results for this experimental test of Darwins sexual selection hypothesis?

Answer 9

RESULTS:
Controls not significantly different so combined in graph

Why are the tails not usually as long as the manipulated elongated ones?
Males with lengthened tails had greatest success- as predicted by sexual selection theory

Question 10

Describe the mating calls of male tungara frogs

Answer 10

Calls of male tungara frog attract females for mating + predators
- Some calls consist of whine
- And others add chuck components- which is better at attracting females but comes with a cost as also attracts bats (predator)
= trade off between natural selection and sexual selection

Question 11

Define: sexual selection

Answer 11

= discrete form of natural selection that favors traits that increase an individuals ability to gain mates

Question 12

Name the similarities and differences between sexual and natural selection

Answer 12

similarities =
- variation between individuals
- Variation is inherited

Differences =
- natural = variation affects survival
- Sexual = variation affects reproductive success

Question 13

What does selection favour?

Answer 13

Lifetime fitness- compromise between maximal survival and mating success

Question 14

Describe an example that shows that selection favours lifetime fitness

Answer 14

Male survival maximized by a tail length that optimizes aerodynamics (green line) = stabilizing selection for tails of intermediate length as super long tails are impacted by natural selection as less likely to survive
Male mating success depends on mean female mating preference = long tails- so longer the tail = greatest mating success (blue line)
But tails will evolve to an equilibrium
= compromise between natural selection and sexual selection

Question 15

What is sexual selection the result of?

Answer 15

result of competition within species between individuals of the same sex in order to be selected by the opposite sex for reproduction

Question 16

Who discovered sexual selection?

Answer 16

Charles Darwin

Question 17

What was the name for Darwins book relating to sexual selection?

Answer 17

The descent of man and selection in relation to sex = sexual selection important in the evolution of species including humans not down to chance

Question 18

Who did not believe in sexual selection and what were his thoughts instead?

Answer 18

Alfred Russel Wallace believed in natural selection but did not believe in sexual selections instead he thought:
- Male-male fighting = another example of natural selection
- Brilliance of male plumage is due to excess in vitality
- Sexual dimorphism is the result of natural selection

Question 19

Name the 2 components of sexual selection

Answer 19

Intersexual selection
Intrasexual selection

Question 20

Define: intersexual selection

Answer 20

Intersexual selection (=between) = individuals of one sex select among the individuals of the other sex as mates (often female choice)
- selection for traits in one sex that are attractive to the other sex

Question 21

Define: intrasexual selection

Answer 21

Intrasexual selection (=within) = member of one sex, most often males, compete with each other for mating access to the other sex
- selection for traits conferring an advantage in competition with the same sex

Question 22

Name and define the 2 types of traits associated with intrasexual selection

Answer 22

pre-copulatory traits (e.g. weaponry) = all traits that are present before mating

post-copulatory traits (e.g. sperm competition, infanticide) = traits present after mating

Question 23

Is sex ubiquitous?

Answer 23

No but many organisms seem to favour sex over asexual reproduction

Question 24

What is the biggest evolutionary disadvantage of sexual reproduction?

Answer 24

twofold cost of males

Question 25

Explain the two fold cost of males

Answer 25

If each female produces 2 offspring - Sexual female = produces on average a male and female offspring = numbers are stable - Asexual female = produces 2 daughters = numbers double in generation the overall reproductive success of a sexually reproducing population is reduced compared to an asexually reproducing one- a mutation in a sexual population that causes females to reproduce asexually will spread to fixation in just a few generations The fact that asexuality is so rare shows that there must be strong advantages to sexual reproduction that compensate for the twofold cost of producing males

Question 26

Name and explain 4 disadvantages of sexual reproduction

Answer 26

Question 27

Name one advantage of sex

Answer 27

Recombination of chromosomes

Question 28

Name and explain what slows adaptation in asexuals

Answer 28

Clonal interference = when multiple beneficial mutations arise independently within a population of organisms undergoing adaptation through natural selection- these compete for fixation relevant in asexual populations because there is no recombination to bring together beneficial mutations into a single individual

Question 29

Explain what this picture is showing

Answer 29

1. In an asexual population that is initially fixed for the genotype abc 2. beneficial mutations A, B, and C arise independently in different individuals at their respective loci 3. Mutation A is the most fit by chance, and eventually it drives the clones that carry mutations B and C to extinction. 4. A new mutation occurs, reintroducing versions of B and C, but C goes extinct 5. Finally, the population acquires all three mutations when B occurs in a genotype already carrying A, and C occurs in a genotype that already carries A and B. = clonal interference, where multiple beneficial mutations compete for fixation before coming together in the same genetic background which takes many generations due to lack of recombination in asexuals

Question 30

Explain how recombination is advantageous

Answer 30

In a sexual population, recombination can bring together in a single genotype several mutations that originally appeared in different individuals. This reduces clonal interference and accelerates adaptation. The asexual population is therefore at greater risk of extinction in changing environments

Question 31

Explain this picture

Answer 31

In a couple of generations, the genotype ABC arises as genes shared- allows for rapid adaptation ABC mutations occur at same time but due to sex it allows for different versions of genes to come together in just a couple of generations to form ABC type Recombination speeds adaptation to the ever changing environment

Question 32

Define: mullers ratchet

Answer 32

inability to separate advantageous and deleterious mutations leads to the accumulation of detrimental traits due to lack of recombination in asexuals

Question 33

Explain this picture depicting mullers ratchet

Answer 33

red = deleterious mutations (-) Blue = advantageous mutations (+) No recombination = asexuals: 1. 1st + mutation appears in genotype carrying 2 - mutations, resulting in reduced fitness and eventual loss 2. 2nd + mutation arises in a genotype with one - mutation but cannot rid itself of the deleterious mutation due to the lack of recombination 3. This genotype spreads to fixation Recombination = sexuals: 1. By chance, a + mutation ends up without any - mutations 2. This is selected for and spread to fixation throughout population - the beneficial mutations can recombine away from deleterious mutations on the chromosomes where they first appeared, and into genotypes