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lecture 15 - Sexual Dimorphism Sexual dimorphism is the...

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Sexual Dimorphism Sexual dimorphism is the existence of physical differences between the sexes, other than differences in the sex organs
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Why? Males compete for females Alterations affect their ability to: Fight Be noticed Find females
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Antennae Males of many insect species have antennae that are more elaborate than females
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Function Males have more surface area on each antenna More surface area = more sensory capability Male moths find females by following a pheromone plume emitted by the female Sensitive males find the female first
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Disruptive Selection i.e., selection against the mean Females have skinny antennae; no need for expensive plumose ones Males with plumose antennae fine females first
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Male mosquitoes have more plumose antennae, respond solely to frequency of female wingbeat Again, sensitive males find the female first
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Dimorphism in ornamentation – Hercules and rhinoceros beetles
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Stag beetles – Lucanus spp.
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What is the benefit of exaggerated dimorphism?
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Sexual Selection
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