11-02-11 (Mal)Adaptation 3

11-02-11 (Mal)Adaptation 3 - ZOL 445 Evolution November 2...

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ZOL 445 Evolution November 2, 2011 Spandrels of San Marco Exaptations : Biological Spandrels Exaptation is a process by which a trait is used for a function other than that for which it originally evolved 1. Exaptations may arise through co-option of one function to another a. Evolution of feathers: from thermoregulation flight b. Horn beetle horns b.i. Distal-less (dll) directs cells to differentiate into legs… b.ii. …but it’s been co-opted to direct cells to differentiate into horms 2. Exaptations may arise because of selection on a pleitropic trait a. Say Trait 1 is being selected for, rather than trait two… b. In female hyenas (who have a pseudopenis): Masculinized genitalia may be a side-effect of selection on elevated pre-natal androgen levels, which also increases aggressiveness Once they have arisen, exapatations may be modified or maintained by natural selection The reason traits arise may not reflect current functions On some level, all adaptations are exaptations, since they initially arise through non- adaptive mutation and are subsequentially modified by natural selection Perhaps a better approach is to distinguish current function from evolutionary origin and accept that they might (indeed are likely to) be different. Processes that shape trait form and function:
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This note was uploaded on 12/21/2011 for the course BIO 202 taught by Professor Brooks during the Fall '11 term at UCSB.

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11-02-11 (Mal)Adaptation 3 - ZOL 445 Evolution November 2...

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