Bio-335-Topic11

• Asexual reproduction


  • No courtship
  • No gametes
  • 100% gene transfer
• Sexual reproduction


  • Lottery hypothesis (random mix)
  • Coevolution hypothesis (helps in interactions)
  • Repair hypothesis (recombination increases repair)
• Hermaphroditism

  Simultaneous vs successive
• Dioecism


  • Division of labor between genders
  • 50:50 or benefit to underrepresented gender
• Gender determination by parents


  • Selective fertilization for females vs males
  • Temperature control/environmental control
• External fertilization


  • Timing for gamete release
  • Common for aquatic species
• Internal fertilization


  • Possible on land
  • Allows sperm storage and implantation delay
• Copulation


  • Anatomical modifications
  • Ovulation induction
• Polygyny


  Multiple females mating with one male
• Monogamy


  One male and one female mating
• Anisogamy


  Evolution from isogamy (equal-sized gametes)
• In ancestral population, individuals produce different-sized gametes
• Fixed amount of energy to allocate to gametes ... size-number trade-off
• Zygote viability related to size
• Bateman's hypothesis

  • Female reproductive success most strongly limited by # and success of eggs
  • Male reproductive success limited by # of mates
• Primary sexual characteristics

  Genitalia and reproductive organs
• Secondary sexual characteristics

  Morphological differences between sexes not directly involved in reproduction
• Parental investment theory


  Sex with greater investment in offspring production should be choosier about mates
• Weapons


  Exaggerated morphological traits used in male-male competition
• Ornaments


  Exaggerated morphological traits used to attract females
• Operational sex ratio


  Ratio of sexually receptive males to females
• Mormon Crickets have spermatophores that are 25% of their body size
• Mate choosiness varies with resource availability
• Intersexual competition

  Exaggerated characteristics to attract mates
• Intrasexual competition


  • Sexual dimorphism in polygamous species
  • Males differ in timing to adulthood
  • Dominance hierarchies in polygamous species
  • Larger mandibles, antlers for battle
• Southern Elephant Seal males show sexual dimorphism correlated with mating success
• Alternative mating strategies

  • Subordinates gain female trust, form male alliances
  • Small males "preload" sperm
  • Satellite males
  • Conditional strategies
  • Genetically determined alternative strategies
• Isopods have genetic differences yielding 3 sizes in males, with similar reproductive success
• Sperm competition

  • Males may remove rivals' sperm
  • Males may guard females post-copulation
  • Males should guard if high probability female will mate again
• Linoleic acid in copulatory plug decreases interest in future matings in females
• Damselfly copulation involves a "wheel formation"
• Dunnock males remove competitor's sperm
• Blue Milkweed Beetle females check for cantharidin from males
• Seychelle's Warbler males guard model eggs
• Hens eject sperm of subdominant males
• Hanging Fly copulation is related to nuptial gift size
• Intrasexual competition


  Competition between individuals of the same sex for access to mates
• Sexual dimorphism in polygamous species


  Differences in physical characteristics between males and females in polygamous species due to sexual selection
• Males differ in timing to adulthood


  Males in polygamous species may take longer to reach sexual maturity than females due to competition for mates
• Dominance hierarchies in polygamous species

  Hierarchies established by males in polygamous species to determine access to mates based on factors such as size, strength, or age