Sexual selection

Question 1

Why is one sex choosy while one competes?

Answer 1

• Relative differences in reproduction rates
• Relative difference in gamete cost

Question 2

“Choosy Selection”
Species, indirect and direct benefits

Answer 2

Getting the right species
* Hybrids are less fertile or fit
* Happens in overlapping environments
Direct benefits
* Food
* Nesting or laying site
* Protection
* Parental care
Indirect benefits
* Parasite resistence
* Longetivity
* Sexiness

Question 3

Long-tailed widow birds

Answer 3

• Malte Anderson’s experiments
• Males have extremely long-tail - suggesting a role in amte choice
• Experiment by trapping males
• Shorterned some tail, lengthened others and some stayed the same
• Females prefered long-tailed males

Question 4

Sedge warbler song

Answer 4

• Clive catchpole’s study on song
• Song can be recorded and anaylsed using a sonogram
• Songs are made out of elements
• More elements mean a larger repertoire
• Males with a large repertoire get preferred
• Experimentally produced songs induced a greater female response

Question 5

Fisher’s runaway theory

Answer 5

• Female preference for a trait becmoes genetically linked with the trait, which could lead to a greater reproductive success as more females prefer it
• Arbitary - no cost or benefit (brown eyes)
• Natural selection to start with - a benefit (e.g. preference for faster runners)
• Sensory bias to start with - cost (loud calls or obvious signals are percieved first)

Question 6

Handicap theory

Answer 6

• Long tails are expensive handicaps
• Females prefer them as they signal a males ablity to survive despite the handicap
• May be a reliable signal of male viablity
• Females select for a useful trait rather than a arbitary one