Lecture 19 - Lecture 19 Feb 18 Evolutionary Processes...

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1 Lecture 19: Feb. 18 Evolutionary Processes: Sexual Selection Bateman-Trivers’ principle - female fitness is limited by resources - male fitness is limited by number of mates Intra - vs. Inter sexual Selection Male-Male competition - combat vs. displays - sperm competition Female Choice - direct benefits - indirect benefits: good genes and/or sexy sons Discussion Activity this Week Article on Sexual Selection (week 8 folder) Complete essay due by Feb. 22 Exam 2: Monday, March 3 Covers lectures 12-22 (22=review); Optional Review Session on March 2 Check Qwizdom Points on SAMS https://cats.lsa.umich.edu/ Chapter 24 : 523-527 Sexual differences include differences between the sexes in morphology, behavior, and/or physiology. Morphology Behavior Physiology includes differences in hormones and brain structure Sexual selection Process by which individuals that possess certain heritable traits are more successful at obtaining mates and thus reproduce at a higher rate relative to other individuals in the population Generally speaking, Males compete more intensely for mates than do females & Females are choosier about their mates than are males. Why is this pattern prevalent? Answer: Anisogamy Anisogamy is defined by the occurrence of gametes of different sizes Males make many, many small gametes, called sperm . Females make a fewer, large gametes, called eggs . Eggs are expensive whereas sperm are “energetically” cheap.
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2 Bateman & Bateman & Trivers Trivers ’ principle principle : Difference in gametic investment between males and females leads to THREE PREDICTIONS . Prediction #1 : male fitness will be limited by the number of mates, whereas female fitness will not. Bateman Bateman ’s Rule: s Rule: only male fitness improves with # mates. 1
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Lecture 19 - Lecture 19 Feb 18 Evolutionary Processes...

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