#### GROUP MEMBERS

Erika Hunter
Polyprep Preparatory Country Day School, Brooklyn, New York

Eugene McNicholas
Kittatinny Regional High School, Newton, New Jersey

Linda Needham

Galina Pavlova
Clara Barton High School, Brooklyn, New York

Celeste Payne

#### ORGANISM

Spike the Iguana (Iguana iguana)

#### BACKGROUND

Iguanas are ectotherms and typically live in warm environments.  It is important to keep contact between the iguana and humans to absolute minimum.  Holding the iguana would typically increase its temperature close to human body temperature.

In Dynamics of Dinosaurs and Other Extinct Giants, R. McNeill Alexander presented an equation which states that:

where the leg length equals the combined length of the femur, tibia/fibula and the ankle.  Speed is in meters per second.  Leg length is in meters per second.  Gravitational acceleration is in meters per second squared.

#### PROBLEM

What is the effect of temperature on the speed of an iguana?  The speed is reflected in the stride length.  A faster speed will be accompanied by a longer stride length.

#### HYPOTHESES

1. If the temperature of Spike's environment increases, then his speed will increase.

2. (rejected because time cannot be measured to calculate speed)
3. If the temperature of Spike's environment increases, then his stride length will increase.

#### MATERIALS

 butcher paper heat lamp metric ruler meterstick TI-83 graphing calculator masking tape Vernier calculator-based laboratory (CBL) unit unit-to-unit link cable Vernier CBL DIN adapter Vernier temperature probe Casio QJ700 Digital Camera

#### PROCEDURE

1. With a metric ruler, measure the various lengths of the segments of the iguana’s limbs within a container.
2. Place the iguana under a heat lamp.
3. Measure 4-1m segments of a piece of butcher paper approximately 5m long.  Place a meter-stick along the length of the first measured interval.
4. Label one end of the paper as the start point and one as the finish point.
5. Using a temperature probe (with the aid of a CBL and graphing calculator program), record the surface temperature of the iguana.
6. Focus the digital camera on the first two meters of the butcher paper.
7. Remove the iguana from the container and place at the start point.
8. Release the iguana and digitally record its movement along the meter-stick.
9. **  Make sure to record the final surface temperature of the iguana.
10. Repeat steps 5-9 five times.
11. Once the iguana has stopped moving, return it to the container.
12. Repeat steps 6-11 once the surface temperature of the iguana has dropped approximately 8- 10?C.
13. Download images from digital camera onto Adobe Photo Deluxe.  Determine and analyze the stride length from hindlimb to same hindlimb using Scion Image.  An animation can also be produced of the igauna’s movement using Paintshop Pro 5 Animation Shop.

#### DATA

##### Spike's Measurements
 Limb Segment Length (cm) Forelimb (right) shoulder to inner elbow 1.2 inner elbow to tip of longest finger 3.5 Forelimb (left) shoulder to inner elbow 1.2 inner elbow to tip of longest finger 3.5 Hindlimb (right) hip to knee 2.1 knee to ankle 2.2 ankle tip to tip of longest toe 3.9 Hindlimb (left) hip to knee 2.3 knee to ankle 2.2 ankle tip to tip of longest toe 3.9

Ambient room temperature: 24 degrees Celsius

#### DISCUSSION AND CONCLUSIONS

The data collected strongly supports our hypothesis that Spike’s stride length would increase as his temperature increased. When warm, we observed the iguana to be more alert and moving quickly as the data show by a positive slope (refer to the above graph).  In addition, when cool, we observed the iguana to move considerably slower.  The negative slope of the graph supports this observation as well (refer to the above graph).

However, there was also a degree of human error when this activity was performed.  For example, in the procedure, “**” refers to data that should be taken but was not.  A reading of body temperature taken after each of the iguana’s runs should have been reported as this would have been the starting point for the next trial run.  This data would be significant when interpreting the data from the trials when the iguana was warmer.  Since iguanas are ectotherms, their temperature is regulated by the environment and the cooler surface may have begun to affect its temperature and therefore its stride length.  We further conclude that there was not enough data for an accurate determination of dimensionless speed and considerably more data should have been collected.

##### Questions for Students
• What other organisms might serve as good subjects for this exercise? Why?
• How could more accurate data be measured?
• Why might we want to determine dimensionless speed in examining the stride length of organisms?
• Why is the design of an experiment important?  How might you perform this investigation without the use of the CBL and graphing calculator?
• What are the dependent and independent variables?
• What might happen if you perform the same investigation with a hamster?  Is this organism an ectoderm also?