BILD 3 - Lecture 18

BILD 3 - Lecture 18 - Cheating Sometimes stickleback fish...

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Cheating Sometimes stickleback fish males in poor physical condition may exhibit a bright red area that signals to other males that they are dangerous foes and to females that they are desirable mates. They are counterfeiting a signal that says they are healthy and vigorous. Other types of signal, such as body size or the loudness of a challenge call, however, are more difficult to counterfeit. Thus, it can be predicted that cheating will be rare when the signals that are being selected are honest and difficult to counterfeit. If this is what usually happens, then in most populations cheaters will be rare and will only survive because the targets of the cheating behavior will occasionally mistake a cheater for an honest signaler. But cheaters should be common in situations in which it is easy to counterfeit a signal. There are many ways to cheat, and we will see some other examples later.
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Honest signals and cheaters in sticklebacks. The size of the red spot indicates the male’s health , but it is easy to “fake,” making it easy for less vigorous males to cheat. A bird’s song is an example of an honest signal. It has been shown in zebra finches that the length and complexity of a song can be adversely affected by poor food during development or by treatment with hormones during development that raise stress levels.
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SHORTAGE ISONE TREATMENT
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Thus, a long, high-pitched and complex song is indeed an honest signal of health in these birds, and would be difficult to fake! The Evolution of Cooperation Most organisms behave selfishly most of the time, because such behavior will tend to increase their Darwinian fitness. But there are many examples of cooperation within species, ranging from food sharing among vampire bats to cooperative hunting behavior in a wide variety of animals. There are also many examples of cooperation between species, leading to mutualistic relationships in which both species benefit. The evolution of all these behaviors may have initially involved some degree of altruism . Altruism is the behavior of an individual that may lower its own Darwinian fitness at the same time as it increases the Darwinian fitness of other members of its group. Often, the cooperating animal is actually harmed by behaving cooperatively. Why should you give up some of your food to other members of your group, when this might lower your chances of survival? How did cooperative behavior evolve in the face of the possibility that the fitness of the potential cooperators might be lowered, and in spite of cheaters? There are two major mechanisms by which altruistic behavior might evolve: kin selection and reciprocal altruism. Kin Selection and Inclusive Fitness The fitness of an organism may not be fully described even if we measure the survival of its progeny and determine its Darwinian fitness. An organism may increase its fitness by aiding its relatives to have offspring, a process called kin selection . Remarkably, even if the organism itself dies without leaving offspring, so
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This note was uploaded on 06/10/2010 for the course BILD 3 taught by Professor Wills during the Spring '07 term at UCSD.

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BILD 3 - Lecture 18 - Cheating Sometimes stickleback fish...

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