24.4: Evolutionary EcologySexual Selection: Darwin was faced with problems such as, traits that didn’t seem to favor survival, altruistic social behavior, and unnecessary ornaments. SO: he came up with sexual selection, which explains that these traits help one sex (usually male) compete for the opposite sexes’ attention so they can successfully mate. *surviving means nothing if you don’t reproduce offspring to carry on your genesIntra-sexual Selection: selection generated by competition of individuals within the same sex. Inter-sexual Selection: “Female choice” Mating success occurs because the females prefer to mate with males that have certain traits (the traits that Darwin thought didn’t favor survival) that favor successful mating. Why do females get to choose and the males have to compete?Females have few, large gametes (eggs)While males have many, small gametes (sperm)It is more costly for females to mate than it is for males. Males have a massiveamount of opportunity to mate because if they make a bad choice of a mate, theycan go out the next day and redo it. However, if a female makes a bad choice, she has wasted a lot more time and energy and has less opportunity to try again. Therefore, it is crucial that they get it right. Maintenance of Variation: technically natural selection would be expected to remove variation because it favors the most successful traits. Balancing selection: where the heterozygous form is more successful then either of the homozygous forms. EX: sickle cell anemia heterozygous form is mostly healthy and has theadded advantage of being resistant to malaria. Factors increasing variation: Mutation- adds allele back in at very slow rateHidden variation- a recessive allele that is ‘hidden’ in the heterozygous form will
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