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United States (301,293)
01:119:115 (806)
D'arville (38)
Lecture

Ch. 20

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School
Rutgers University
Department
Biological Sciences
Course
01:119:115
Professor
D'arville
Semester
Spring

Description
Ch. 20 Sexual Selection 4/10/12 Differential investment in reproduction • Females generally make greater investment • Quality • Fixed • Males sperm is “cheap”. They don’t invest much Quantity • • Vast Male fitness increases with # of matings. So... Males are relatively indiscriminate • Males compete Female fitness does not increase with the # of matings. So... Females are selective • Females choose **rare exception: sex role reversal: females compete and males choose • When the males contribute the resources Ex: girls compete for baseball players even though they are only ok Mating strategies • Inter-sexual selection: one sex chooses a mate • Females strategies: a) Requirements • Genetic variation in male trait b) Benefits • Direct Benefits: male provides resources that enhance survival fecundity • If nuptial gift too small: she leaves before insemination • Ex. Food (nuptial gift) • Indirect benefits: male more fit, so offspring more fit (good genes hypothesis) • Good gene hypothesis • Female choice in absence of male investment • Beauty contest c) Consequences • Sexual dimorphism (male traits exaggerated) • Intra-sexual selection: • Males often compete for breeding locations access to females Ex: elephant seals ...establish harems, <20% of males mate, fight to the death • • Ex: bonobo chimps mate all the time for social benefit • Male strategies: evolutionary to compete with other males and combat female choice • Infanticide: males kill young after taking over a pride to bring females into sexual receptivity • Copulatory plugs: genitalia obstructed after mating • Deters males (snakes, bugs) • Coercion: Homosexual ‘rape’- male renders other male so there is no competition • • Spiny headed worm: copulatory plug (‘cement’) renders competitors ‘sterile’ • Heterosexual ‘rape’ • Ducks: female can control sperm from fertilizing • Cricket: female takes males wings • Traumatic insemination • Bed bug: male stabs female, injects her with sperm, while she is sucking blood of humans • Beetle: stingers to hurt her so she wont mate again • Mate guarding: • Bank swallow: males guard females during their fertile period • Prolonged copulation: form of mate guarding
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