Evolution of Diploidy

Advantages:

• Second set of genetic information provides a backup in case of somatic mutations
• Increases genetic diversity that may or may not be expressed
• Provides conditions that allow for sexual reproduction

Sexual Reproduction

At first glance, sexual reproduction appears wasteful compared to asexual reproduction (e.g., "cost of males"). The following explanations have been advanced:

• Muller's Ratchet: Mutations accumulate in asexual lineages as there is little chance to get rid of them again.
• "Vicar of Bray" hypothesis: Ability to combine individually advantageous rapid adaptability to change
• Red Queen Hypothesis:

Sexual Selection and Ornamentation in Males

Species recognition

<Sexual selection>: refers to the process by which changes in gene frequencies result from individuals that are better than others at either competing for or at attracting mates -- it is the evolution of traits based on differences in mating success among individuals if (1) some traits increase the ability to compete with individuals of the same sex for access to mates, or (2) some traits increase the ability to attract individuals of the opposite sex.Males are the competing sex. Several potential mechanisms have been proposed:

• Intersexual Choice: Why does she consider the trait "attractive"?
  • Nuptual gifts: spermatophore; territory, protection, resources; courtship indicative of parental investment. e.g., Dung beetle
  • "Good Genes Hypotheses": general state of health, indicator of viability and quality.
    • Hamilton and Zuk's "Revealing Signal Theory": bright ornaments reveal a genuinely healthy individual in good condition
    • Zahavi's "Strategic Choice Handicap Theory": the presence of a costly trait is indicative of otherwise good underlying genes that allow an individual to prosper despite this handicap
  • "Passive Attraction Theory": Sensory Bias, conspicuous signals make an individual more likely to attract the attention of a mating partner
  • Fisher's "Run-away Selection": "Sexy Sons Hypothesis", allignment of morphological characteristic and preference for it
  • Genetic Compatibility: MHC locus genes in human mate choice
• Intrasexual competition and interference: winners gain mates, dominance rights, desirable territory, or other advantages that will tend toward transmitting its genes to future generations at higher frquencies than the loser's genes
  • Precopulatory: ritualized contests, loudest signal, masking of call; dominance in social groups; territorial exclusion; alternative mating strategies; sexual interference
  • Postcopulatory: sperm competition: e.g. primate mating systems; anti-aphrodisiacs; mating plugs; partners remain attached e.g. wolves; mate guarding; Bruce effect; Infanticide

Reading Assignment

• Wikibooks: Animal Behavior - Chapter 4

Food for Thought

"Women need a reason to have sex - men just need a place” -- Billy Crystal ... or ... Why does sexual selection produce weird ornamentation in males and rarely in females?

Links of Interest

• Birds do it, Bees do it
• Charles Darwin: Chapter on Sexual selection in the Selection in Relation to Sex (1871)
• Hamilton, W.D., Axelrod, R. & Tanese, R. (1990). Sexual reproduction as an adaptation to resist parasites. PNAS: 87, 3566-3573
• Scent of a man - the MHC perfume