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Chapter 12

Chapter 12.docx

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BIOL 2400
Cortland Griswold

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Chapter 12: After Conception  Life-history theory explores how the schedule and duration of key events is an organism’s lifetime are shaped by natural selection. It helps explain variation in the age at which organisms begin reproducing, the size and number of offspring produced, the amount and type of parental care invested, and even the onset of senescence  Life history – the investment an organism makes in growth and reproduction. Life- history traits include an organism’s age at first reproduction, the duration and schedule of reproduction, the number and size of offspring produced, and life span 12.1 Selection across a Lifetime  Trade-offs arise when allocation of resources to one life-history trait reduces investment in another trait  Investment in reproduction often comes at the expense of growth or body maintenance  Selection may favor alleles that are beneficial early in life, even if those same alleles are harmful later on  Investment in reproduction early in life often reduces an individual’s ability to breed later in life 12.2 Parental Investment  Females generally benefit more than males from parental care of offspring. Exceptions to this rule, when they occur, provide exciting tests of sexual selection theory  Frequency-dependent selection can maintain variation within populations, if the fitness of an allele or phenotype decreases when it is common, and increases as it becomes rare. This may contribute to the persistence of two sexes (males, females) within populations  The Trivers-Willard hypothesis predicts greater investment in male offspring by parents in good condition, and grea
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