11+PCB+4674+-+Sexual+Selection+-+no+Clicker

Sexual Selection

• Definition of Sexual Selection

  • A form of natural selection focused on competition to mate with individuals of the opposite sex.

  • Often distinguished from survival selection, as it emphasizes reproductive success.

Key Concepts in Sexual Selection

• Intra-sexual Selection

  • Males compete with each other for access to mates, leading to the evolution of sexual weapons.

• Inter-sexual Selection

  • Males attract females through desirable traits; leads to the evolution of beauty.

Conditions Favoring Sexual Weapon Evolution

• Sexual weapons develop in contexts where males must compete for females or defensible resources.

• These adaptations can be seen across various species: mammals, beetles, crabs, etc.

Evidence for Female Choice

• Females possess the predominant role in mate selection, based on three main hypotheses:

  1. Good Genes/Good Parent Hypothesis

     • Females select mates based on traits that indicate genetic quality.

     • Evidence: Coloration in birds correlates with lower parasite loads.

  2. Aesthetic Choice Hypothesis

     • Females choose males based on beauty alone, independent of utility.

     • Concept of Fisherian runaway where traits and preferences co-evolve over time.

  3. Sensory Exploitation Hypothesis

     • Females select males based on traits that stimulate their pre-existing sensory preferences.

• Example: Túngara frogs prefer males with complex calls, linking preference to common food sources.

Trade-offs in Sexual Ornamentation

• Evolution of sexual ornaments entails a balance between attractiveness and survival utility.

• Cost of maintaining or displaying these ornaments can impact overall fitness.

Historical Context

• Charles Darwin's Perspective

  • Emphasized male competition: "Victory will depend… on having special weapons, confined to the male sex."

  • Suggested that beauty in males serves a purpose in reproductive success.

• Alfred Russell Wallace's Insights

  • Proposed experiments to understand female choice and ornament significance in mate selection.

Case Studies

• Harlequin Beetle

  • Males engage in competitive battles over territories around female egg-laying sites.

  • Long forelimbs are evolutionary adaptations enhancing competitive success.

• Peacocks and Other Birds

  • Male peafowl display impressive plumes that attract females.

  • Darwin noted this inclination for strategy in sexual selection, further explored by Wallace.

Conclusion

• Sexual selection is a complex interplay of competition, mate choice, and evolutionary developments that drive species diversity, enhancing understanding of adaptation and reproductive strategies.