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Choosing a mate and reproductive strategies are based on methods to succesfully pass on genes
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Voles Prairie Monogamous Both parents care for young More receptors Montane Nonmonogamous Mother cares for young briefly Less receptors Same levels of oxytocin
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Sexual Dimorphism
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Human Females: ~1 egg/month Human Males: 250,000,000 sperm/ ejaculation Fig 46.12
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I hope Pat likes my feathers because I am tired of dragging them around everywhere. Fig 23.15
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1 2 Which is male?
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1 2
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Sexual Dimporphism: morphological differences between males and females
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Sexual Dimorphism
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Male barn swallows have longer tails than females
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Why do males have long tails? From “Biological Science” 3 rd ed. by Scott Freeman -fig 51.5
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Why do males have long tails? From “Biological Science” 3 rd ed. by Scott Freeman -fig 51.5 feathers cut and reattached captured and released
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Female grizzly bears cannot reproduce while lactating. Therefore they can only reproduce every once every 3 years…
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…this leads to competition between males
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Male elephant seals compete for access to females in limited beach territories. They are on average 4 times bigger than females. Male elephant seals weigh ~3 tons. From “Biological Science” 3 rd ed. by Scott Freeman -fig 25.14
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Competition between males is fierce, only a few males father most of the offspring. 90% of males never successfully reproduce 60% of females do not successfully reproduce From “Biological Science” 3 rd ed. by Scott Freeman -fig 25.14
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Average height/weight by sex in U.S.
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Ratio of Weight Male/Female M/F
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Primates have different reproductive stratagies
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Testes Compared to Overall Weight Testicle size (oz) per body weight (lbs)
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Our closest living relative... bonobos
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http://www.youtube.com/watch?v=eubDSQrFakohttp://www.youtube.com/watch?v=eubDSQrFako Stop at 1:53 http://www.ted.com/talks/lang/eng/isabel_behncke_evolution_s_gift_of_play_from_bonobo_apes_to_humans.html
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Pipefish: related to seahorses
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Pregnant Male: Males care for developing eggs
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If differences in reproductive behavior and morphology are based on sex roles, what happens when the roles are reversed? Males care for developing eggs
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The Measurement of Sexual Selection Using Bateman’s Principles: An Experimental Test in the Sex-Role-Reversed Pipefish Syngnathus typhle (2005) Integrative and Comparative Biology, 45:874–884 Adam G. Jones, Gunilla Rosenqvist, Anders Berglund, and John C. Avise
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Jones et al. Fig. 1 frequency number of mates When there are more females than males, many females cannot mate.
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frequency number of mates Jones et al. Fig. 1 When the sex ratio is even, most males and females mate.
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frequency number of mates Jones et al. Fig. 1 When there are more males than females, most males can mate.
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Jones et al. Fig. 1 The sex ratio affects who will successfully reproduce. Pipefish females are more affected by competition.
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number of individuals body length (mm) Jones et al. Fig. 4 Excess females: only medium size females can mate
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number of individuals body length (mm) Jones et al. Fig. 4 Excess males: many different size males can mate
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Jones et al. Fig. 4 medium sized female pipefish are most successful at reproducing while size is less critical for male pipefish
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...So when males invest more resources for reproduction, they become the limiting factor and are choosier about mates. Pipefish males care for developing eggs
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Different reproductive strategies lead to differences in sexual dimorphism.
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In light of differences between male and female resources for reproduction, how does this affect equality between males and females?
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Do we want equal treatment of men and women? How should equality be attained, or how should the inequality be regulated?
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Reports due Take-home available soon, Due in one week
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