Section Notes, March 5.docx

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Department
Organismic and Evolutionary Biology
Course
Organismic and Evolutionary Biology OEB 53
Professor
Andrew Berry
Semester
Spring

Description
OEB 53 S ECTION March 5, 2013 Divergence of Character  Competition between similar forms >> divergence of character, due to selection allowing later  generations to adapt to new niches or habitats  Species w/more mutations, or in other words, evolve faster (diverge faster), will be more successful  because there is more material for natural selection to work on  Diagram: extinction of B­D, while A’s descendants take over niches originally occupied by B­D  Each surviving lineage derives from the successful ancestor, note that really only one lineage comes  out successfully, eliminating species with similar niches  “Living fossil”: does not diversify  Even if you find a fossil resembling present­day organisms, it may have only been closely related to  the ancestor of present­day organisms, not necessarily the ancestor itself, just a sister species to the  ancestor. Sexual Selection  Depends on struggle of males for possession of females  A specific type of natural selection to modify one sex with respect to the other sex  Less rigorous than natural selection  More intense in polygamous species  Most likely when males and females share a strong sexual dimorphism  Male­male: ex. salmon fighting with hooked jaws  Female choice: birds exhibit a more ‘peaceful’ form where the males do not fight but compete for the  attention of females with flamboyant displays  Sexual selection can very rapidly select for traits… what is stronger, natural or sexual selection? Extinction  New species constantly forming but finite # of species >> extinction  Rarer forms + competition  Proof of evolution vs. creationism OEB 53 S ECTION  Ex. Longhorn cattle went extinct, pushed out by 
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