Lecture 5 readings chapter 10 pg. 363 – 375
Chapter 10 – Studying Adaptation: Evolutionary Analysis of Form and
A trait that increases the fitness of its possessor is called an adaptation
Adaptationist program – demonstrating that the traits of organisms are indeed
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
Experiment: there were to treatments: cattle with the oxpeckers and cattle without
The experiment showed that oxpeckers have no discernable effect on their host’s
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
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.
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
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
Prof Andrade, Evolutionary Biologyenters were able to cut the wings off25 September 2012wing of
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.
replaced +Marked wing
(marks + wave (marks +operation,
+operation) no wave)
Intact +House-fly wing (no marks, no wave,
(marks + wave, (wave +operation, no operation)
no operation) no marks)
Tephritid flies House flies
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
-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
Statistical test: P<0.01 therefore you reject the null hypothesis
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