What are the 2 components of sexual selection?
- Male-male competition where males compete for a female
2. Female mate choice (due to aesthetics?)
How did Anderson prove causation in elaborate males having more sexual success?
Used the widow bird, cut tails off some and glued on to others to produce an abnormally long tail
Found preference for an exaggerated trait
How is there unequal sexual investment between males and females?
- Starts with the difference in gametes (anisogamy)
- Females have greater investment in offspring whereas males have greater reproductive potential
Give an example of sex role reversal
In Ephippiger
- Good conditions mean that female crickets are more fussy and males never reject mates
- Bad environmental conditions means that female crickets are less fussy and males reject mates
Give an example of sexual conflict
Cricket Cyphoderris strepitans
- Females feed on males hind wings during copulation
- Males have evolved hooks to secure females, if shaved virgins have no disadvantage (full wings) but non-virgins need them to secure a female for copulation
What is a ‘runaway’ process?
Process by which there is an increasing frequency of traits and preferences in a population through selection arbitrary attractive traits - coevolution of male sexual signals and female preferences
How can runaway sexual selection lead to speciation?
If males evolve different signals/attractive traits in different locations which are then not attractive to other female populations
What is adaptive sexual selection?
Where females/offspring gain an advantage through a choice of mate
What is a resource based mating system?
Where sexually dimorphic males will provide good territory, help feed the offspring/female
How can males cheat a resource based system?
Some insects evolve fly-like appendages on legs to trick females
What is Zahavi’s handicap mechanism?
Whereby females select traits that are expensive and deleterious as male with the best genotype is likely to be the one with the biggest handicap
Trait should be condition-dependent
Does the opportunity to choose a mate increase offspring viability?
Yes, demonstrated with flies in lab conditions with choice mating vs random mating
What did Molle’s swallow experiments show?
That females preferred longer tails and that longer tails had increased mite resistance, even when fostered in a different nest
