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A Recap Regarding Senescence

A Recap Regarding Senescence. Selection is more powerful in the stages up to the age of peak reproductive value If a pleiotropic gene is introduced that gives an benefit early in life, at the expense of a cost much later on, than it will be selected

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A Recap Regarding Senescence

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  1. A Recap Regarding Senescence • Selection is more powerful in the stages up to the age of peak reproductive value • If a pleiotropic gene is introduced that gives an benefit early in life, at the expense of a cost much later on, than it will be selected • Senescence is the outcome of such negative effects later in life

  2. The Evolution of Sex The Mathematics Urge Sublimated

  3. What Use is Sex? • The Problem: • Asexual: 100% copy in offspring • Sexual: 50% (usually) copy in offspring • So why do some species have sex? • Some answers: • Genetic “proofreading” • Certainty of environment • Parasite resistance

  4. The Genetic Manuscript • “We are no4 ready for winter” • What is the correct letter? • A second copy from another organism of the same species may help • After “proofreading,” some recombination takes place • New genotypes are produced

  5. The Certainty of the Environment • Offspring produced in environments similar to parents: • Asexual reproduction • Offspring reproduced in environments dissimilar to parents: • Sexual reproduction • Gambling theories are not well supported by the data

  6. Parasite Resistance • Parasites are responsible for far more deaths than physical threats • Correlation between high parasite infestation and amount of recombination • Sex allows for new genetic “locks” to keep out old parasite “keys”

  7. Hermaphroditism • Simultaneous hermaphroditism • When sexual functions serve both sexes • Sequential hermaphroditism • Generally due to maturation and size-advantage • Separate sexes • When sexual functions do not serve both sexes

  8. Eggs & Sperm • “Cheating” organisms may produce a greater number of smaller gametes • Disruptive selection: • organisms producing many small gametes or fewer large gametes vs. producing average gametes

  9. Minimum Investment • Females in most species have a greater minimum investment in offspring than males • Ova • Gestation • Lactation… • Male & female “needs” differ due to minimum investment

  10. The Sex Ratio • If males can inseminate several females, why do we have 1:1 ratio? • Reproductive efficiency? • Island with 90 men & 10 women vs. 10 men & 90 women • Frequency dependent selection

  11. Sexual Dimorphism • Intrasexual contests • Lead to dimorphism of competing sex relative to other sex • No intrasexual contests leads to females typically being larger • Ova production

  12. The Wrap-Up • Evolution of sex • Proofreading • Gambling • Parasite resistance • Sex ratio • Minimum investment • Sexual dimorphism

  13. Things to Come • Long-term mating strategies • Female • Male • Short-term mating strategies

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