Notes on Behavioural Ecology and Sexual Selection

Interactive Module Overview
  • Interactive module for understanding behavioural ecology concepts.
  • Reading/interactive component available all term.
  • "Quiz yourself" component available until March 14th, 2025.
  • Access SimBio on Quercus under the Lectures Module.
Sexual Dimorphism
  • Definition: The phenomenon of different genotypes and/or phenotypes among sexes of the same species.
  • Key aspects of sexual dimorphism:
    • Differences in gametes (anisogamy).
    • Differences in reproductive organs.
    • Other phenotypic differences associated with sex.
  • Example: Anglerfish illustrate pronounced phenotypic differences.
Understanding Sex
  • Language clarification:
    • Genetic males (e.g., XY in humans, ZZ in birds) vs. genetic females (e.g., XX in humans, ZW in birds).
    • Gametic males vs. gametic females.
  • Focus on average traits between sexes, with potential for variation within a sex.
Evolution of Sexual Dimorphisms
  • Questions to consider:
    • Why do sex-specific traits and behaviours evolve?
    • Why is there variation in traits and behaviours within sexes?
  • Explore reasons behind such evolutionary traits.
The Nature of Sexual Selection
  • Charles Darwin's concept of sexual selection:
    • “Depends on the advantage which certain individuals have over others of the same sex and species, in exclusive relation to reproduction.”
  • Sexual selection consists of:
    • Intrasexual selection: Competition between individuals of the same sex.
    • Intersexual selection: Choosiness, usually observed in females.
Factors Determining Strength of Sexual Selection
  • Variance in mating success affects sexual selection strength.
  • Operational sex ratio definition: The ratio of sexually competing males to females.
  • Factors that can alter operational sex ratio:
    • Anything that modifies receptivity of one sex or their potential for remating.
Parental Investment Theory
  • Proposed by Robert Trivers (1972).
  • States that reproductive investments differ between sexes:
    • Males invest little (small, mobile sperm) and thus compete for mating opportunities.
    • Females invest significantly (large, resource-rich eggs) limiting their rate of reproduction.
Mating Strategies and Behaviours
  • Two strategies for sexual selection:
    • Intrasexual selection (competition) vs. intersexual selection (mate choice).
  • Variations in strategies observed in species such as side-blotched lizards.
    • Three male strategies: Orange (defensive), Blue (guarding), Yellow (sneaker).
  • This diversity in mating strategies illustrates a rock-paper-scissors dynamic in nature.
Bateman Curves Overview
  • Revisiting how mating success influences fitness.
  • Males exhibit higher variance in reproductive success compared to females, resulting in stronger sexual selection.
Summary of Key Concepts
  • Conspicuous ornaments puzzled Darwin, leading to the evolution of sexual selection as a concept.
  • Strength of sexual selection is influenced by gamete investment, operational sex ratios, and competition among sexes.
  • Variability in traits and strategies is maintained under negative frequency-dependent selection where rarer traits gain advantages over more common ones.
Additional Resources
  • Videos referenced for visual understanding include "Nature’s Greatest Dancers" and specific behaviours of birds-of-paradise.