Sexual selection Flashcards
Sexual conflict
Intra- sexual selection : male-male competition. There is sexual dimorphism e.g. In size. Infanticide is an extreme case of this
Inter- sexual selection : between the sexes. The female chooses which male to mate with
Why is there a battle of the sexes?
1- anisogamy, there is a difference in male and female gametes
2- females are limited in egg production, so increase success by being choosy
3- makes increase success by mating with as many females as possible
Selection hypotheses 1
Good genes- direct benefit
The female relies on external measures of genetic quality and chooses the best signal.
Reliable because only makes with good genes can express the trait (strategic choice handicap model). Signal is an indicator of quality (a stags points correlate with age and survivorship).
Genetic compatibility rather than good genes for everyone? Choose dissimilar, but not too dissimilar.
Selection hypotheses 2
Sexy sons, runaway selection hypothesis (Fisher 1930)
Some traits are strongly preferred by females. Male offspring are more likely to possess the preferred trait, and female offspring are more likely to possess preference.
Selection hypotheses 3
Sensory biases: females may have biased that males can exploit in their sexual signalling. The bias may predate the trait.
E.g. Tungstate frogs, females naive to ‘chucks’ in calls prefer calls with chucks added.
Bowerbirds, correlation between female colour preference and male bower decorations. Females prefer to eat a certain colour of fruit, which is predominant in bower colours.
Sensory bias may be driving the evolution of exaggerated signals
Why don’t male traits get bigger and bigger?
Benefits may become offset by the survival cost of maintaining the trait.
Webers law- difficult for female to discriminate differences with ever exaggerated traits (e.g. Tungara, females only prefer exaggerated up to a point, too much = no preference)
It can become costly and time consuming
