1323384764_CHAP_10_SPR - EVOLUTION/LECTURE1 Evolution (PCB...

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EVOLUTION/LECTURE1 file:///E|/CH10-ADAPTATION-SPRING-2008/CHAP_10%20SPR_2008.HTML[12/8/2011 2:53:48 PM] Evolution ( PCB 4674 ). Chapter 10. Studying adaptation: Evolutionary analysis of form and function Main topics of lecture: I: Introduction: 1.- All hypotheses must be tested: The giraffe's neck reconsidered 2.- Experiments and observational studies 3.- The comparative method II: Phenotypic plasticity: III: Trade-offs and constraints: 4.- Factors that limit adaptive evolution 5.- Female flower size in a Begonia: A trade off 6.- Flower color change in a Fuchsia: A constraint 7.- Shifts in a herbivorous beetle: Constrained by lack of genetic variation I: Introduction: 1.- All hypotheses must be tested: The giraffe's neck reconsidered 1.1.- How can a researcher rigorously test the hypothesis that a particular trait is adaptive? This is an important question in evolutionary biology, mostly because we showed in the previous lectures that other evolutionary mechanisms different from selection are also important in evolution. In this lecture will give an introduction on how researchers can detect natural selection in all of its forms. 1.2.- As we mentioned in previous lectures, a trait, or integrated suite of traits, that increases fitness of its possessor is called and adaptation and it is said to be adaptive . Roughly speaking, in order to demonstrate that a trait is an adaptation, we need first to determine what the trade is for and then show that individuals possessing the trait contribute more to future generations lacking it. 1.3.- Obvious explanations for adaptation are no so obvious!!! The traditional adaptive hypothesis for the origin of the giraffe's neck (to forage trees above the reach of their competitors) provides an example that no explanation for the adaptive value of a trait should be accepted simply because it is plausible and
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file:///E|/CH10-ADAPTATION-SPRING-2008/CHAP_10%20SPR_2008.HTML[12/8/2011 2:53:48 PM] charming. 1.4.- Traditionally the hypothesis used to explain the adaptive value is known as the foraging-competition hypothesis , if this hypothesis is correct, then during the dry season, when food is scarce, giraffes should spend most of their time foraging above the reach of their competitors. In fact, THIS IS NOT THE CASE , giraffes spend much of their dry-season foraging time browsing on low bushes and not tall trees (!!!!). 1.5.- Even when giraffes forage above the reach of their competitors, they seldom forage at a level anywhere near their maximum height (Fig. 8.2). Figure 8.2.: These graphs show the proportion of time males (left) and females (right) spend feeding at different heights 1.6.- Simmons and Scheepers offered and alternative scenario for the evolution of the giraffe's neck. They suggested that the giraffe's neck evolved as a weapon, used by the males in combat over opportunities to mate (Fig. 8.3) Check this site: http://www.ctap3.org/_lperry/africa/giraffes.htm you will see how giraffes use their necks and heads as clubs for fighting!!! Figure 8.3.: Males giraffes use their heads and necks as
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This note was uploaded on 01/11/2012 for the course PBC 4674 taught by Professor Ortega during the Spring '12 term at FIU.

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1323384764_CHAP_10_SPR - EVOLUTION/LECTURE1 Evolution (PCB...

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