BIOB51 Reading 2 [Page 40, 41: Figure 2.3] –LECTURE 3 READING
Evolutionary change in soapberry bugs
-This bar graph shows that the soapberry bugs found in nature on flat podded golden rain trees
have in average shorter breaks than bugs found on balloon vines. The balloon vine is native
to southern Florida, while the flat podded golden rain tree is from Asia during the year 1920. The
data below the x axis show the mean beak length of bugs reared in the lab on fruits from the
balloon vine VS. flat podded golden rain tree.
-The scatter plot shows the beak lengths of female soapberry bugs from Florida in museum
collections [each data point represents one individual].
[Page 42, 43; Other examples] –LECTURE 3 & 4 READING
Vestigial structure: useless version of a body part that has an IMPORTANT function in other species.
Some examples are:
- Brown kiwi – a flightless bird; tiny short wings
- Boas: trace hind [back] limbs, represented internally by simple hips and leg bones and externally
by minute spurs
- The evolutionary understanding of these vestigial structures are that both kiwis + boas descended
with modification, from ancestors in which wings or hind legs were fully formed + functional.
- Humans also have VS. The coccyx [tiny tailbone] + muscles that are attached to the hair follicles
that contract to make our body hair stand on when we are cold or scared (Goosebumps). If we
were bigger, we would look like chimpanzees more scary + intimidating.
- Chickens have 3 digit hands + 4 digit feet. But inside of its embryo, it has this invisible digit that
disappears. WHY? The evolutionary explanation is that birds[chickens] are descended from
tetrapods that had 5 digits. The modifications in the development that transformed the ancestral
limbs, into wings and birds feet take place after the 4 + 5 digit begin to form.
- Vestigial traits also occur at the molecular level
[page 367-371] –LECTURE 5&6 READING
10.2 Experiments: Experiments are the most powerful method for testing hypotheses. A good
experiment restricts the difference b/w study groups to single variable.
What is the function of wing marking + wing waving display of the tephritid fly zonosemata? - The Z fly has distinctive bands on its wings. The fly holds its wings perpendicular to its body and
waves them up + down [the dance she did]. Scientists had noticed that this display seems to
mimic the leg waving, territorial threat display of jumping spiders. People suggested that since
spiders are fast + have a nasty bite; fly mimicking a spider might be AVOIDED by other
predators. A man named Erick had a different idea; since jumping spiders prey on a lot of the Z
flies. Erick proposed that the fly uses its wing markings, and wing waving display to intimidate
the jumping spiders.
- Hypothesis 1: the flies do NOT mimic jumping spiders
- Hypothesis 2: the flies mimic jumping spiders
- Hypothesis 3: the flies mimic jumping spiders + this mimicry functions specifically to discourage
predation by the jumping spiders themselves.
- To test the alternatives Erick needed flies with some parts; not all
- Biologists found that they could cut the wings off Z fly+ glue them back + the cut the wings off Z
fly, and replace them with the wings of housefly [ which are clear + unmarked]. Erick was trying
to see when other predators + jumping spiders approached this fly*, if the predators would retreat,
stalk, attack + kill ..
- They starved 20 of the spiders
- Look at the graph on page 369 for RESULTS
Erick’s study illustrates important points [page 370]
Defining + testing effective critical groups are important.
All of the treatments [controls + experiments] must be handled correctly
Randomization is key for equalizing others, this is a way to avoid bias.
Repeating the test on many individuals is important. It is true in experimental [and observational]
work that larger sample sizes are BETTER. This is because the goal of an experiment is to
estimate a quantity.
Replicated experiments do TWO things:
- They reduce the amount of deformation in the estimate caused by unusual individuals or
circumstances. For instance 4 of 10 Z flies were marked with wings that were attacked on before
they had a chance to display.
- Replicated experiments allow researchers to understand how precise their estimate is by
measuring the amount of variation in the data. Knowing how precise the data are allows the use
of stat tests.
IN SUM, Erick’s experiment was successful because it allowed independent tests of the effect that
predator type, wing type + wing display on the ability of Z flies to escape predation. Experiments are the
most powerful means of testing hypotheses about adaptation.
Read 10.1 BOX.
[Know observational studies on page 372-375] see section 10.3-LECTURE 5&6 READING
Some hypotheses are difficult to rest with experiments. Like why giraffes necks are so tall? To do
so, one would have to make giraffes that are identical in all respects expect the lengths of their
necks. When an experiment is impractical, a careful observational study may be the next best
method for evaluating a hypothesis.
Behavioral thermoregulation: Majority of organisms are ectodermic, meaning that their body
temperatures are determined by the temperatures of their environments. Iguanas can survive short
exposures to body temperature as low as 0 and as high as 47, But they can function only between 15 and 45. Within this narrow range, cold iguanas run and digest SLOWLY, tire quickly + hear
poorly. As they get warmer, they run + digest faster.
The relationship between physiological performance and temperature is called a thermal
performance curve. The shape of the desert iguana’s thermal performance curves is typical of
those of a variety of physiological processes in a diversity of organisms. We can predict that
ecotherm will display behavioral thermoregulation. That is, ectotherms should move around in
the environment so as to maintain themselves as or near the temperature at or near the
temperature at which they perform the best.
As the temperature of the environment changes, animals such as iguanas regulate their body
temperature by moving into the sun to warm up ort into the shade to cool off. The iguanas prefer
to maintain themselves at body temperatures. An iguana may not know when to run away from
the predator. In nature, though iguanas may not always have a sufficient range of environmental
temperatures to move amount to maintain themselves.
Note that although we have asserted the desert iguanas themromoregulate, the fact that iguanas
captured in nature are usually at or near their optimal body temperature does not, by itself prove
that they are active in maintaining those the mid to high 30s. To prove behavioral
thermoregulation, we must show - that the animal in question is choosing particular
temperatures more often that it would encounter those temperatures if it simply moved at random
through its environment.. - that its choice of temperature is adaptive.
Do Garter Snakes Make Adaptive Choices when Looking for a Nighttime Retreat?
-Ray made a study of thermoregulatory behavior of the snake; snakes are affected by temperature in the
same way as desert iguanas EXCEPT for garter snakes, the optimal temperature, preferred temperature +
maximum survivable temperature are all a few degrees lower than the corresponding temperatures for
iguanas. Ray implanted small radio transmitters to snakes. Each implant transmitter emits a signal that
allows biologist with a handled receiver and an antenna to find the implanted snake even when the snake
is hiding. Also the transmitter reports the snakes temp by changing the rate at which it beeps!!
- The garter snakes stay at temperatures between 28 – 32 degrees. Ray found that snakes in nature
do a great job of thermo regulating in the same range. But question is how do the snake’s thermo
regulate so well? The two snakes in the figure spent the day under or near rocks. Other options
include moving up + down a burrow + staying on the surface of the ground while moving back +
forth from sunshine to shade.
- Ray and his friends compared the relative merits with these thermoregulating strategies by
watching the environmental temp under rocks of various sizes + depths of burrows.
- A snake under a thin rock would not get dangerously cold at night but would overheat in the
daytime. “As ray says, the snake would be dead by 11 am and remain dead til 6pm”. A snake
under a thick rock would remain safe all day but would never reach its preferred temp. ROCKS
of medium t