Sexual selection (Meg) Flashcards
Name an example of a simultaneous hermaphrodite
leopard slug
How do leopard slugs mate?
mating pairs hang from mucus thread while copulating- mate at night time
Name an example of a sequential hermaphrodite
clown fish
Name a species that reproduces almost entirely by self fertilisation
cactus
How do bacteria like e-coli reproduce?
use conjugation and other mechanisms to exchange genetic material
How do angler fish reproduce?
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
What is Darwins sexual selection hypothesis?
secondary sexual traits increase mating success
Describe the method of an experimental test of darwins sexual selection hypothesis
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
What were the results for this experimental test of Darwins sexual selection hypothesis?
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
Describe the mating calls of male tungara frogs
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
Define: sexual selection
= discrete form of natural selection that favors traits that increase an individuals ability to gain mates
Name the similarities and differences between sexual and natural selection
similarities =
- variation between individuals
- Variation is inherited
Differences =
- natural = variation affects survival
- Sexual = variation affects reproductive success
What does selection favour?
Lifetime fitness- compromise between maximal survival and mating success
Describe an example that shows that selection favours lifetime fitness
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
What is sexual selection the result of?
result of competition within species between individuals of the same sex in order to be selected by the opposite sex for reproduction
Explain the two fold cost of males
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
Name and explain 4 disadvantages of sexual reproduction
Explain what this picture is showing
- In an asexual population that is initially fixed for the genotype abc
- beneficial mutations A, B, and C arise independently in different individuals at their respective loci
- Mutation A is the most fit by chance, and eventually it drives the clones that carry mutations B and C to extinction.
- A new mutation occurs, reintroducing versions of B and C, but C goes extinct
- 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
Explain this picture
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
Explain this picture depicting mullers ratchet
red = deleterious mutations (-)
Blue = advantageous mutations (+)
No recombination = asexuals:
- 1st + mutation appears in genotype carrying 2 - mutations, resulting in reduced fitness and eventual loss
- 2nd + mutation arises in a genotype with one - mutation but cannot rid itself of the deleterious mutation due to the lack of recombination
- This genotype spreads to fixation
Recombination = sexuals:
- By chance, a + mutation ends up without any - mutations
- 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
