sexual selection

Question 1

Bateman’s principle

Answer 1

male fitness is limited by the number of mate obtained ( so males fight )

females fitness is limited by offspring quality
( so females choosy )

in most species, variability in reproductive success is greater in males than in females

Question 2

parental investment

Answer 2

any investement by the parent in aindividual offspring that increases the offsprings chance of surviving at the expense of future offspring

Question 3

parental investment theory : Trivers, 1972

Answer 3

the sex which exhibits less parental investment ( not necessarily male ) will have to compete to mate with the opposite sex

in species where both sexes invest heavily they should be mutually choosy

Question 4

intra-sexual selection

Answer 4

members of the same sex compete for mates

e.g southern elephant seal

Question 5

inter-sexual selection

Answer 5

where members of one sex ( usually female ) choose members of the opposite sex

selection of the mate is dependent on their ‘attractiveness’

Question 6

direct phenotypic benefits

Answer 6

choosy individuals receive direct benefits from their mates
- food, breeding territory, parental care, ect.

e. g male damselfish defent territories
- females choose mates on the basis of their terriotory and e.g size
- female choice influences egg survival

Question 7

spermatophores

Answer 7

male reproductive structures that package sperm cells to aid in their transmission to females during mating in a variety of invertebrate animals

Question 8

sensory bias

Answer 8

female mating preferences may be by-products of selection on sensory systems
(males evolve traits that exploit these biases)

e.g Xiphophorus swordtails (and relatives)
- swordlessness is the primitive state (ancestoral state)
- female platyfish prefer conspecific males
with artifical sword
- a pre-existing bias for swords

Question 9

Fisherian runaway selection

Answer 9

Fisher (1930) : male ornamentation is the result of female preference for males with the most exaggereated ornaments

• initial female presence is arbitary
• strong female choice for the male
  ornament results in runaway sexual
  selection, leading to the further
  exaggeration of the trait
• preference for the trait (in females)
  becomes genetically linked to the
  expression of the trait (in males)
• continues until the costs imposed by
  natural selection balance the benefits of
  sexual selection

Question 10

sexy son hypothesis

Answer 10

assumes an indirect benefit to female choice due to the attractiveness of their sons

females that mate with an attractive male will produce attractive sons
- their fitness will be increased as a result
of their sons’ higher mating success

( closely related to the Fisherian runaway selection )

Question 11

indicator traits : handicaps

Answer 11

the handicap principle : reliable signals must be costly to the signaller
- only high quality individuals can afford the cost of the signal

if signals are cheap, all individuals can display them, so they provide no information to the receiver

Question 12

Hamilton-Zuk hypothesis (1982)

Answer 12

a special case of the handicap principle

sexual ornaments are indicators specifically of parasite and disease

e.g intestinal nematoads adversly affect male secondary sexual characters

Question 13

runaway selection vs handicap principle

Answer 13

runaway :
• genes for attracting females only
• signal and prefernce for signal become linked
• no positive relationship between signal and genetic quality
•signal negatively or uncorrelated with condition

handicap principle :
• genes for survival/reproduction, not just attractivness
• not necessary for signal and prefernce to be linked
• signal positevly associated with genetic quality
• signal may be positively associated with condition

Question 14

lek

Answer 14

aggregation of male animals gathered to engage in competitive displays and courtship rituals

Question 15

the lek paradox

Answer 15

• strong skew in male reproductive success
• a few generations of mating should elimante most genetic variation
• yet females remain choosy