Lecture 5 readings chapter 10.docx

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Biological Sciences
Maydianne Andrade

Lecture 5 readings chapter 10 pg. 363 – 375 Chapter 10 – Studying Adaptation: Evolutionary Analysis of Form and Function A trait that increases the fitness of its possessor is called an adaptation Adaptationist program – demonstrating that the traits of organisms are indeed adaptations 10.1 All hypotheses must be tested: Oxpeckers Reconsidered Experimenter: Paul Weeks Oxpeckers and cattle are thought of to have a mutual relationship, where the oxpeckers feed on the ticks that are found on the cattle and the cattle gets cleaned. However closer analysis reveals that the oxpeckers occasionally eat the ticks but the ticks have indigestible material that is sometimes regurgitated by the birds. The birds do lick blood from a wound, probes the host’s ear (for wax) and scissors the host’s hair (for dead cells). Although the cattle attempts to shoo them off it hardly ever works. Experiment: there were to treatments: cattle with the oxpeckers and cattle without oxpeckers Results The experiment showed that oxpeckers have no discernable effect on their host’s tick loads The cattle with the oxpeckers present took a longer time for the wound to heal and the wounds with the oxpeckers took longer to heal. Cattle exposed to oxpeckers have considerably less earwax (don’t know if this is beneficial) The results show that oxpeckers are parasitic However a key flaw is that cattle is NOT the oxpeckers native host Experiment by Alan McElligott studied relationship between rhinos and oxpeckers and the results were similar. This example shows us that all hypotheses must be tested. 10.2 Experiments Well-designed experiment allows us to isolate and test the effect that a single, well- defined factor has on the phenomenon in question. What is the function of the wing markings and wing-waving display of the Tephritid fly Zonosemata The tephritid fly Zonosemata vittigera has distinctive dark bands on its wings When disturbed the fly waves its wings up and down. These displays mimics the territorial threat of jumping spiders Experimenter: Erick Greene (1987) Question: Do the wing markings and the wing waving display of Zonosemata vittigera mimic the threat displays that jumping spiders use on each other, and thereby allow the flies to escape predation? Hypothesis 1 – the flies don’t mimic jumping spiders (null hypothesis = no effect). Hypothesis 2 – the flies mimic jumping spiders, but the flies behave like spiders to detect other, non-spider predators Hypothesis 3 – the flies mimic jumping spiders (deter predation by the jumping spider) Prof Andrade, Evolutionary Biologyenters were able to cut the wings off25 September 2012wing of another fly. There were five different treatments: zonosemata untreated, zonosemata with its own wings cut andi) Planned Experimentwith housefly wings, housefly with zonosemata wings and housefly untreated. Experimental groups Wing removed, replaced +Marked wing (marks + wave (marks +operation, +operation) no wave) Intact Intact +House-fly wing (no marks, no wave, (marks + wave, (wave +operation, no operation) no operation) no marks) Tephritid flies House flies (fig. 10.6) The different responses that the spider could have would be to retreat, stalk and attack, or kill. The spiders were starved then the flies were presented to the spiders in random order. Results -The jumping spiders retreated from the flies that had marked wings and waving wings but attacked the others. -When the test flies were presented to other predators they were captured and eaten Statistical test: P<0.01 therefore you reject the null hypothesis Conclusion Wing-waving display and markings mimic jumping spider displays and reduce predation by jumping spiders Things to keep in mind when conducting an experiment  Defining and testing control groups is critical  All
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