Evolution 4 - 1 Today • A note on the debate over social...

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Unformatted text preview: 1 Today: • A note on the debate over social vs. sexual selection • Wrap-up adaptation • Review 4 modes of natural selection • Speciation Roughgarden on “Social Selection” • One way to think about it: • What limits an organism’s reproductive success? If “access to mates” Sexual Selection If “survival of young” Social Selection Collared Flycatchers Great Frigatebirds 2 All over the world, cormorants are great flyers… 3 … except in Galapagos! (where they are flightless) Reduced wing: May well be a localized adaptation for foraging 4 Now consider cormorant’s black plumage: An adaptation for thermoregulation after swimming in cold Galapagos waters? Exaptation • A character previously shaped for another function for another function is coopted for a new use! Conolophus Amblyrhyncus 5 Conolophus Amblyrhyncus Exaptation • A character previously shaped for another function is coopted for a new use! • No history of selection for current function 6 In most circumstances, Darwin may well have been right… But differential replication can occur on different levels: Group 7 A lot to be said for gene-level selection: • Dawkins: Natural selection acts by the preservation of genes responsible for favorable variation, and the elimination of unfavorable genes unfavorable genes. • The result, says Dawkins, is reproductive selfishness • Selection works against any measure of reprod. altruism Back to Tambopata Rain Forest… 8 Meet the cordyceps fungus! Amazing degree of selfishness!! 9 • But many organisms show a measure of “self-sacrifice”… • Is it “ altruism ”? Belding’s Ground Squirrel • Consider Belding’s Ground Squirrel P. Sherman 1977 Science 197: 1249 “Alarm Call!” Why don’t males do more alarm calls? 10 As ground squirrels mature, males are chased off… (prevents inbreeding) Result: groups of closely related females live in close proximity Relatives share genes identical by descent! The proportion shared depends on the relationship: “r” is coefficient of relationship “r” measures proportion of shared genes r “Individual fitness” • Effectiveness of design for (your own) survival and reproduction 11 But because genes are shared, there’s a probablility that copies of...
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This note was uploaded on 11/08/2009 for the course HUMBIO 2A taught by Professor Boggs,c;durham,w during the Spring '08 term at Stanford.

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Evolution 4 - 1 Today • A note on the debate over social...

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