Wiens-lecture3-24Mar - Outline Evolutionary Processes Today...

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Outline Evolutionary Processes Today Finish population genetics Briefly discuss maintenance of variation Briefly discuss limits on evolution Begin species and speciation
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Quick Review What have we learned so far? What is the original source of genetic variation? What is another source of new variation in a population? What happens when there are few individuals in a population? What process can cause large changes in allele frequencies in large populations with little gene flow with other populations?
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Population Genetics Sexual Selection Darwin saw a potentially big problem in his theory of evolution by natural selection Many traits that organisms have seem to actually decrease their chances of survival! Darwin proposed the idea of “sexual selection” to explain the evolution of these traits (published important book in 1871 “The Descent of Man and Selection in Relation to Sex”)
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Population Genetics Sexual Selection In many species, males have elaborate ornaments or behaviors (songs, calls, visual dispays) Ornaments often used in contests between males over females (intrasexual selection) and/or in attracting females (intersexual selection) But these traits seem likely to decrease their chances of escaping predators and/or getting food
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Sexually-selected Traits in Animals
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Population Genetics Sexual Selection Selection may favor individuals traits that increase reproductive success, even at the expense of survival Sexual selection = differential selection as a result of variation in the ability to obtain mates Traits favored by selection increase fitness (relative contribution of a given phenotype to the next generation), but there are different ways to increase fitness (more matings per year for fewer years vs. fewer matings for more years)
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Population Genetics Big Question in Sexual Selection Why should females prefer males with elaborate ornaments and other traits? In some cases, male trait indicates direct benefits (e.g., male with better display has larger territory, more resources for female and young) In other cases, male trait has no obvious benefit to female “Good genes”: only healthy males can make ornaments (male displays offer reliable information to females in choosing mates) “Sexy son” hypothesis (male with display will have attractive offspring with high fitness)
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Maintaining Variation
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