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Lecture 9

BIOL 2400 Lecture 9: Sexual Selection Class Notes

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University of Guelph
BIOL 2400
Teresa Crease

BIOL*2400 Dr. Crease Winter 2017 Sexual Selection Lecture 9 Morphological differences between sexes is Sexual Dimorphism o Differences between sexes influence reproductive fitness via success in obtaining males = Sexual Selection Can operate if theres heritable differences in a trait that affects mating success Often works very differently in males and females Eggs are more expensive to produce that sperm Monogamy: one male pairs with one female o Sexual: partners mate with each other exclusively o Social: partner pair but may cheat Polygyny: males mate with multiple females Polyandry: females mate with multiple males Females are limited by fecundity Males are limited by number of mates they can obtain Members of sex that is subject to strong sexual selection will be competitive o Compete for: Access to opposite sex Resources required by opposite sex Members of sex that is subject to weak sexual selection will be choosy Competition among members of one sex for access to the opposite sex, or to resources required by opposite sex = Intrasexual Selection Evolution of behaviour to attract members of opposite sex that are choosy = Intersexual Selection Evolution of features used to fight with other members of same sex to gain access to members of opposite sex Malemale competition leads to extreme variance in reproductive success Female choice can lead to elaborate morphologies and courtship displays o Phenotypes and behaviours may decrease bearers fitness with respect to viability o Benefit obtained in terms of mating success outweighs loss of viability, traits will persist via Sexual Selection Why are Females Choosy? Good Genes Hypothesis o Courtship indicates genetic quality of male Courtship provides resources to female andor her offspring (nuptial gifts) Males evolve courtship to exploit preexisting sensory bias in female Preference is arbitrary but leads to runaway sexual selection: SexySon Hypothesis o 1. Females develop arbitrary preference of variant in male trait
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