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Chapter 10

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BIOL 359
Jonathan Witt

BIOL359 - Evolution Winter 2013 Chapter 10: Studying Adaptation: Evolutionary Analysis of Form and Function - Rock pigeons: Tiny hooks on the tips of their beaks, better able to kill the feather-eating lice while preening, maintains superior feather, better at keeping warm, evading predators & attracting mates - Experiment: Captured 26 pigeons, trimmed the tip of their beaks o Hookless pigeons grew lousier, heavily infested with parasites o Those allowed to regrow their hooks had falling parasite loads - Adaptation: A trait or integrated suite of traits, that increases the fitness of its possessor o Individual possess the trait contribute more genes to future generations than individuals lacking it - Conventional wisdom can be dangerously seductive, all hypotheses must be tested 10.1. All Hypotheses Must Be Tested: Oxpeckers Reconsidered - Traditional answer: Oxpeckers need an easy meal of ticks & a safer place to stay, they can also clean the wounds & hosts are happy to oblige in return for a free cleaning  mutually advantageous - Experiment: Divide a herd of cattles into 2 groups o Group 1: Normal visit by oxpeckers o Group 2: Protected from oxpeckers o I: No significant difference between cattle with vs. without oxpeckers in any of the trials  Oxpeckers have no discernible effect on their hosts’ tick loads o II: Oxpecker drinks blood from open wounds, enlarge existing wounds  Wounds took longer to heal when oxpeckers are present o III: Cattle exposed to oxpeckers have considerably less earwax  Oxpeckers eats earwax  Cattles are not natural hosts of oxpeckers, rhinos are - Differences among populations are not always adaptive o At the molecular level, much of the variation among individuals may be selectively neutral - Not every trait of an organism is an adaptation o E.g. Feeding on large mammals did not evolve because it creates mating opportunities for oxpeckers - Not every adaptation is perfect o E.g. Migration of large mammals may expose oxpeckers to the risk of an unpredictable food supply 10.2 Experiments - A good experiment restricts the difference between study groups to a single variable - What is the function of the wing marking & wing-waving display of the Tephritid Fly Zonosemata? o Traditional answer: The wing-waving display of the Tephritid fly mimic the leg-waving territorial threat display of jumping spiders “Mimicry of a predator’s behaviour by its own prey” o H1: Flies do not mimic jumping spiders, maybe it’s for courtship o H2: Flies mimic jumping spiders, but flies behave like spiders to deter other, non-spider predators o H3: Flies mimic jumping spiders to deter predation by jumping spiders o 5 experimental groups of flies were created  A: Untreated Tephritid, test effect of wing markings plus wing waving  B: Tephritid fly own wings cut & re-glued, control for effects of operation  C: Tephritid Fly with Housefly wings, test effect of wing waving without wing markings  D: Housefly with Tephritid fly wings, test effect of wing markings without wing waving  E: Untreated housefly, test effect of no wing markings & no wing waving o Jumping spiders retreat from flies with the wing-waving display with marked wings (A & B), but attacked flied that lack either wing markings, wing waving, or both (C, D, & E).  A & B groups are the controls  B ensures that when group C was eaten, it’s due to the lack of markings on the wing, not because the wings had been cut & glued  Treatments are handled exactly alike, randomization is key, large sample size & test must be repeated multiple times BIOL359 - Evolution Winter 2013 10.3. Observational Studies - When an experiment is impractical, a careful observational study may be the next best method for evaluating a hypothesis - Do garter snakes make adaptive choices when looking for a nighttime retreat? o How do garter snakes thermoregulate their body temperature so well? o Surgically implanted miniature radio transmitters, which reports the snakes’ location & temperature  Thickness of the rock is critical, same for being in a burrow or on the surface  Thin rock: Overheat during the day & underheat at night  Thick rock: Never reach the preferred temperature  Medium: Just right, close to the preferred temperature range all day  Thin, thick & medium rocks are equally available in the environment  Snakes thermoregulate behaviourally by choosing rocks of medium thickness “adaptive choice made by the snakes” 10.4. The Comparative Method - Comparisons among spec
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