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Lecture

Lecture5Feb52013.doc

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Department
Anthropology
Course Code
ANT331H5
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REPRODUCTIVE BEHAVIOUR February 4 , 2013 Male  & Female strategies Sex characteristics John Hunter (1837) Primary  • Sex organs Secondary • Ecological traits • Fighting (males) Darwin (1871) Primary •Related directly to reproduction Secondary •Intrasexual competition Intrasexual competition 1. Outmaneuver or drive away other members of the same sex 2. Attract members of the opposite sex Male Competition • Tends to be more confrontational & intense than females  • male fitness depends on maximizing mating frequency • May lead to earlier death than females Gadgil & Bossert (1970) Trivers (1972) Model to explain earlier Male Mortality Success of male reproductive effort • Dependent on the reproductive effort of male competitors Success of female reproductive effort • Dependent on her own effort & less upon the effort expended by other females  Excessive Male Mortality Cost of Male Reproductive Effort • Direct • Indirect Ultimate Causes of Sex differences in mortality ­ Different reproductive strategies Males greater competitiveness, means greater risks (especially in young males) • Selection for intense male mating effort leading to greater dissolution, death,  disease COMPETITIVE MALES Coolidge Effect •Males are often re­aroused by novel females, as new reproductive opportunities •Male’s reproductive output is limited by his access to fertile females •Males are not limited so much by their physiology, as by their competitors  Male physiology & strategy ANDROGENS Castration • Atrophy of male reproductive organs • Reduced penile erection • Reduced orgasm • Decline in aggression Charles Brown­Sequard (1889) Hamilton & Mestler (1969) • Androgens increase male mortality Other Male Mating Strategies 1.Sneak Fertilizers * e.g. bluegill sunfish 2. Mixed Mating Strategies * e.g. Dung Flies 3. Fighters & Scramblers * Hamilton Types of post­copulatory Competition between males (E.O.Wilson) 1. Sperm displacement 2. Induced abortion & reinsemination 3. Infantic
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