BIO220 Lecture Notes: Sexual Selection and Mate Choice

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Lecture 15: Sexual Selection and Mate Choice
  • Key Outline:
    • Definition and examples of mate choice.
    • The puzzle of choosiness: Benefits of choice.
    • Direct benefits.
    • Indirect benefits ("good genes").
    • Benefits visible in bluegill sunfish.
Revisiting Bateman Curves
  • Analysis of mating strategy.
    • Graph representation of number of mates vs. offspring count.
Intersexual Selection and Mate Choice
  • Definition: Traits (behavior/morphology) influencing mating success of the opposite sex toward preferred types.
  • Terms used interchangeably: mating bias, mating preference, mate choice.
Cues in Mate Choice
  • Visual cues: e.g., Long-tailed widowbird, satin bowerbird.
  • Tactile cues: e.g., Sierra dome spider.
  • Acoustical cues: e.g., Túngara frog, woodhouse’s toad.
  • Olfactory cues: e.g., Moths, mouse.
Mate Choice Experiments
  • Long-tailed Widowbird Experiment:
    • Investigating female preferences for tail length.
    • Tail manipulation: Natural, reduced, elongated, sham surgeries.
  • Outcomes:
    • Mating success ranked as L > N = S > R.
    • Assessment of males’ mating success based on tail length.
Acoustic Cues: Túngara Frog
  • Preference for complex calls leading to mating success.
  • Foraging implications: Frog-eating bats prefer complex calls, leading to trade-offs between mating success vs. predation risk.
The Puzzle of Choice
  • Why elaborate traits?
    • Preferred by mates, leading to selection for those traits.
  • Hypotheses for Choice:
    • Direct benefits: Increase the chooser's offspring output.
    • Indirect benefits: Genetic advantages for offspring, enhancing their fitness.
Examples of Direct Benefits
  • Nuptial gifts and resource provisioning:
    • E.g., Katydid with nutritious spermatophores; longer copulation duration leading to higher sperm transfer.
Selection for Male Traits
  • Indicators of resource availability (territory, parental care).
  • Good genes: Traits indicating high genetic quality preferred by females, influencing offspring fitness.
Alternative Reproductive Strategies: Bluegill Sunfish
  • Parity of parental vs. sneaker/satellite males: Direct benefits (care), indirect benefits (good genes).
  • Offspring size influence on survivability.
Parental Investment Theory
  • Trivers (1972): Different investments lead to competition among individuals of the sex investing less.
Pipefish Reproductive Role Reversal**
  • Investigating male mate choice for larger, fecund females.
  • Assessing influences of environmental factors on reproductive success and mate availability.
Summary of Sexual Selection
  • Sexual selection may favor traits associated with direct benefits to mates or those indicating genetic quality.
  • The investing sex tends to show more choice, while the non-investing sex often competes for access to mates.
  • Environmental influences can shift relative investments and competition dynamics.