Evolutionary Biology 7

Question 1

what is sexual selection the result of

Answer 1

the result of the differential reproductive success that arises from competition for males and access to fertilisation

Question 2

Fisherian runaway selection

Answer 2

runaway sexual selection leading to extreme and physically maladaptive sexual dimorphism

• selection has to be strong enough to undermine natural selection. occurs when the sexual dimorphism trait is linked with the female preference
  e. g. peacock plumage

Question 3

Chaseaway selection

Answer 3

opposite of runaway selection, concerns the situation where males evolve sexually attractive traits which are actually disadvantageous to the female. The females then evolve resistance to the trait and in response the males evolve a more attracting version of the trait to keep attracting the females. and so on

Question 4

five differences between natural selection and sexual selection.

Answer 4

1) SS favours mate acquisiton and fertilisation , NS favours survival and fecundity
2) Can act in opposition on a trait
3) SS is alot stronger and faster acting
4) SS may building linkage disequilibrium more effectively (assortative mating)
5) SS/NS might contribute to divergence whilst the other inhibits it.

Question 5

Ecological interactions with SS

Answer 5

• Food resources
• predation
• parasitism
• sensory bias

Question 6

Example of food resources affecting sexual selection

Answer 6

E.G. Red crossbills , -> 10 ecotypes, highly adapted to species of conifer, with overlapping ranges and minimal gene flow between ecotypes. each ecotype also had distinct call.

experiments showed females selected mates based on feeding efficiency and not call types. (direct system + could be a magic trait)

Question 7

magic trait

Answer 7

when traits subject to divergent selection also contribute to non-random mating. basically involved in SS and NS

Question 8

Example of predation affecting sexual selection

Answer 8

E.g. guppy

• 2 different predation systems
• number of spots on guppy change depending on predation/female preference
• high mortality associated with highly attractive sexual ornaments for males
• no speciation despite rapid co-adaption of male and female reproductive strategies (too much gene flow)

Question 9

How does parasitism affect sexual selection

Answer 9

• can exploit hosts sexual signals
• parasite load has effect on host condition j
• can lead to co-evolutionary cycles to maintain honesty in sexual signalling

E.g. common yellow throat

• black marks costly due to being melanin based
• fitter individuals have larger black marks (related to HHC class II allele which is heavily related to immunity)
• females use marks to pick males, parasites can disrupt this relationship.

Question 10

How does sensory environment relate to sexual selection

Answer 10

• all signals have to navigate their environment
• has to be sent and received to be considered a signal

E.g. Morra et all (2011) experimental evidence

• co-evolved nematode with bacterial pathogen
• resulted in high outcrossing (selection for sex)
• manipulated population to be asexual (rapid extinction)
• sexual pops persisted via reciprocal co-evolution

Question 11

Main difference between sex and asex

Answer 11

meiosis = recombination and segregation

Question 12

where is sexual reproduction found and what is its cost

Answer 12

sexual reproduction fold in higher organisms and has two-fold cost (half offspring cannot produce children)

Question 13

beneficial effects of recombination

Answer 13

• purging of deleterious alleles

- creating new gene combinations