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Sexual Selection

Sexual Selection. Sexual dimorphism is common. Parental investment often differs between the sexes. Male and female seahorses which sex should be competitive and which choosy?. Strategies for the competitive sex often come at a cost. Strategy: Mate a lot!

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Sexual Selection

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  1. Sexual Selection

  2. Sexual dimorphism is common

  3. Parental investment often differs between the sexes

  4. Male and female seahorses which sex should be competitive and which choosy?

  5. Strategies for the competitive sex often come at a cost Strategy: Mate a lot! (Even at the cost of long-term survival)

  6. Strategy 1: • Fight

  7. Galapagos marine iguana Cold water has algae Return to land to warm up and digest Big body allows more efficient grazing Small body has a better metabolic “balance”

  8. * = largest body size at which iguanas could maintain weight in two different years Males lost weight, females were near optimum body weight

  9. Individuals that are too large don’t survive well

  10. Bigger males got better territories The most successful male, iguana 59, got more than four times as many copulations as any of his rivals

  11. Strategy 2 • Advertise

  12. Bright coloration comes at a cost (higher predation on males) Male and Female collared lizards

  13. Male is more vulnerable to predators Male must expend energy on tail

  14. Body condition of males declines over season Experimentallyshortened tails  Less decline in body condition Therefore, long tails do have a cost!

  15. Females didn’t like the shortened tails even though the treatment improved the health of the experimental males over the season Is this choice good for the species? Can the choice be good for a particular female? (yes, if the male has good genes or if her sons are attractive) From Pryke and Andersson (2005).

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