Biology 131 Laboratory Spring 2012 Name Lab Partners ALLOMETRY: DETERMING IF DOLPHINS ARE SMARTER THAN HUMANS? NOTE: Next week hand in this completed worksheet and the assignments as described. Objectives 1. Become familiar with allometric modeling and calculations in biology 2. Evaluate the effects of body size on athletic performance in humans 3. Evaluate the effects of body size on brain size in mammals Background Over evolutionary time organisms have changed in size and body form. All aspects of an animal s biology including its physiology, anatomy, behavior and ecology are influenced by this. Such increases and decreases in size will generally be correlated to changes in body proportions such as length, width, surface area and volume of the animal, with the physics of tissues dictating the limits to how big an animal can grow. Thus, there are a physical reasons why mice the size of cows do not graze in the fields on campus, or that the shape of baby animals are different than adults of the same species (i.e. the head of a puppy is proportionately larger when compared to its parent.) In this lab we will investigate how form and function are linked through allometry, the science of how a biological variable is affected by body size. The value of allometry is in its predictive power. We can t measure all biological parameters of all of the animals of the world; but through allometry we can predict how an animal should function based on its body dimensions. Most important are the animals that don t fit our predictions. Such unique species often provide clues about the adaptations needed to survive in extreme environments or in a changing world. First you need to understand how allometric relationships are calculated. Part 1. Determining an allometric equation Allometric relationships are power functions that take the form, y = ax b where y is some physiological variable of interest (i.e., metabolic rate, grip strength) and x is a body dimension (i.e., mass, length). a is the intercept of the relationship and b is the power exponent.
If you were interested in the speed of dinosaurs in relation to body size you could start with the following data set. Data set: Speed versus body mass in Dinosaurs Body Mass (kg) Speed (km/hr) 100 15.5 250 4.3 500 2.1 1000 1.2 Plot your data on the following graphs (Be sure to note the axis units): A. linear plot 18 16 14 Speed (km/hr) 12 10 8 6 4 2 0 0 200 400 600 800 1000 1200 Body Mass (kg)
B. Log Plot 100 log Speed (km/hr) 10 1 10 100 1000 log Body Mass (kg) In comparison to power relationships, it is relatively simple to generate a predictive regression from a linear relationship. Looking at the above plots you can see why the log transformed data (in b) is so useful. Let s make a few predictions about dinosaurs. Draw a straight line though the data points in plot b. Using this plot, answer the following questions: 1. What is the predicted speed of a dinosaur with a body mass of only 20 kg? 2. If you found a set of dino prints and calculated its speed to be 3 km/hr, how big would you predict the animal to have been that made the prints? 3. The above data is for bipedal (2-legged) dinosaurs. The speed of a 100 kg quadrupedal (4-legged) dinosaur is 2.1 km/hr. Graph this point in the log-log plot. What does this tell you about bipedal versus quadrupedal dinosaur locomotion?
Part 2. The Effect of Body Size on Athletic Performance: Are bigger athletes stronger? An underlying assumption in exercise physiology is that the larger the muscle mass the stronger the individual. Hence, there has been a lot of interest in using steroids to increase muscle mass in athletes. In this part of the lab we will examine the relationship between body size and strength in the human. Grip strength will be used as our metric of athletic performance. For athletes grip strength is critical for excelling in many sports, such as tennis, golf, baseball, football, gymnastics, and rock climbing. We will also evaluate pinch strength which provides a metric of fine-motor strength in the thumb, fingers, and forearm. The underlying question you should be thinking about is, are bigger athletes necessarily stronger? In this experiment, you will measure and compare grip strength in your right and left hands. You will also correlate grip strength with gender, handedness, and height. You will analyze the pinch strength of each of your four fingers and assess the effect of digit length on strength. Important: Do not attempt this exercise if you have arthritis, carpal tunnel syndrome, or any ailment that might be exacerbated by using the muscles of your arm and hand. PROCEDURE Each person in the group will take turns being subject and tester. For each subject measure Total height = cm Length of fingers of dominant hand (base knuckle to finger tip). Record in Table 5. Hand Grip Strength 1. Connect the Hand Dynamometer to the Vernier computer interface. Open the file 16a Compare Grip Strength from the Human Physiology with Vernier folder. 2. Zero the readings for the Hand Dynamometer. a. Hold the Hand Dynamometer along the sides, in an upright position (see Figure 1). Do not put any force on the pads of the Hand Dynamometer. b. Click the Zero button,. 3. Have the subject sit with his or her back straight and feet flat on the floor. The Hand Dynamometer should be held in the right hand. The elbow should be at a 90 angle, with the arm unsupported. 4. Have the subject close his or her eyes, or avert them from the screen. Figure 1 5. Click to begin data collection. After collecting 2 s of baseline data, instruct the subject to grip the sensor with full strength for the next 8 s. Data will be collected for 10 s. 6. Store this run by choosing Store Latest Run from the Experiment menu. 7. Repeat Step 2 5 with the left hand.
8. Determine the maximum and mean force exerted by your hands during a portion of the data collection period. a. Place the cursor over your graph at 4 s and click and drag to highlight both runs from 4 s to 8 s. b. Click the Statistics button,, to see the Statistics box. c. Check the boxes in front of Run 1 and Latest and click. d. Record the maximum and mean force for each run in Table 1. e. Close the Statistics box by clicking the in the corner of the box. 9. Work with your classmates to complete Tables 2 4. Note: In Table 4, round height to the nearest cm. Data for each individual should be written on the board, and the class averages calculated according to the headings in the tables. Pinch Strength 10. Open the file 16b Compare Grip Strength from the Human Physiology with Vernier folder. 11. Have the subject sit with his or her back straight and feet flat on the floor, holding the Hand Dynamometer along the sides in the non-dominant hand (see Figure 2). Note: No additional force should be placed on the sensor by this hand. 12. Have the subject close his or her eyes, or avert them from the screen. 13. Zero the readings for the Hand Dynamometer. a. Hold the Hand Dynamometer along the sides, in an upright position. Do not put any force on the gray pads of the Hand Dynamometer. b. Click the Zero button,. Figure 2 14. Click to begin data collection. Instruct the subject to immediately pinch the end of the sensor between the pads of the thumb and forefinger of his or her dominant hand, and hold for 5 s. 15. Instruct the subject to switch to successive fingers every 5 s. Data collection will stop after 20 s. 16. Determine the mean force applied during each pinch. a. Click and drag the cursor over the first plateau on the graph, representing the pinch strength of the thumb and index finger (see Figure 3). b. Click the Statistics button,, and record the mean pinch strength to the nearest 0.1 N in Table 5. c. Move the brackets to obtain statistics for the second plateau, representing the pinch strength of the thumb and middle finger. As you move the brackets, the statistics in the Statistics box will be updated based on the data between the brackets. d. Record the mean pinch strength to the nearest 0.1 N in Table 5. e. Repeat this process to obtain statistics for the remaining two pinch strengths. f. Close the Statistics box by clicking the in the corner of the box.
Figure 3 DATA Table 1 Individual Grip Strength Data Maximum force (N) Mean force (N) Right hand grip strength Left hand grip strength Table 2 Class Grip Strength Data Average mean force (N) Males (dominant hand grip strength) Females (dominant hand grip strength)
Table 3 Class Grip Strength Data Average mean force (N) Right hand Left hand Right-handed individuals Left-handed individuals Table 4 Class Grip Strength Data Height (rounded to nearest cm) Average mean grip strength of dominant hand Male (N) Female 1.52 m (5 ) or below 1.55 1.63 m (5 1 5 4 ) 1.65 1.73 m (5 5 5 8 ) 1.75 1.83 m (5 9 6 ) 1.85 m (6 1 ) and above Table 5 Individual Pinch Strength Data Length (cm) Mean force (N) Dominant hand index finger Dominant hand middle finger Dominant hand ring finger Dominant hand little finger
ANALYSIS AND ASSIGNMENT Using graphing software (i.e. Excel) or on logarithmic graph paper, graph your data on log-log plots and provide short answers to the following questions. I. Grip Strength Using the data in Table 4 plot grip strength in relation to height. Plot separate lines for males and female averages. 1. Is there a difference in grip strength in your dominant and non-dominant hands? Are you surprised by the result? 2. Examining the data in Table 3, does there appear to be a correlation between handedness and grip strength? Are the results similar for right-handed and lefthanded people? 3. Is there a difference between the grip strengths in the different categories of height for which data was collected in Table 4? What conclusion can you draw about the relationship between height and grip strength? 4. Does gender play a more significant role in grip strength than height? than handedness? II. Pinch Strength Using the data in Table 5 plot pinch strength in relation to finger length. 1. Using the pinch strength data in Table 5, describe the difference in strength between fingers. Where is the difference the largest? Do the length of the fingers make a difference in strength? Is there an obvious allometric relationship? Explain. 2. List at least two possible reasons for the differences you see between the pinch strength of the first two fingers and the second two fingers. In your answer consider actions of the hand and musculature (Us an anatomy textbook or atlas to view the muscles of the forearm and hand).
Part 3. The Effect of Body Size on Brain Size: Are dolphins smarter than humans? Allometric relationships are powerful predictive tools in biology. In this part of the lab we will examine how brain size changes with body mass for different groups of mammals, the primates and the cetaceans. Both are considered to be large-brained relative to other mammals. Here we will use allometry to determine whether body mass or species classification determines brain mass for these mammals. PROCEDURE 1. Examine the skull specimens representing six different species of cetaceans. In the following table record the body mass of each from the attached identification tags. Using a tape measure determine a. total length of each skull b. diameter of the brain case by measuring the width at the base of the skull for each specimen. 2. Record your data for each species in the following table. Brain mass in grams is calculated using the following formula: Brain Mass = 4.2 (diameter/2) 3 Remember to use the proper units (i.e. diameter is in centimeters). SPECIES Body Mass Skull Length Diameter Brain Mass (kg) (cm) (cm) (gm) Killer Whale Beaked Whale Bottlenose Dolphin Ganges River Dolphin Amazon River Dolphin Harbor Porpoise
3. Using the following Log-Log Plots graph the following for all of the specimens: a. Brain mass in relation to skull length log Brain Mass (grams) 1000 100 10 10 100 log Skull Length (cm) b. Brain mass in relation to body mass log Brain Mass (grams) 1000 100 10 10 100 1000 log Body Mass (kg)
4. Answer the following questions. a. Does brain mass appear to be affected by the physical dimensions of the cetaceans? Which appears to be a better predictor for brain mass within this group: skull length or body mass? (This can be assessed by looking at the closeness of fit (correlation) of the data points on a straight line through the data set in each plot- how much variability is there around the line?) c. The allometric regression for brain mass in relation to body mass for primates is Brain mass = 0.0203Body Mass 0.66 where body mass and brain mass is in kilograms. From this relationship we find that a 10 kg primate has a brain mass of 93 grams and a 150 kg mountain gorilla has a brain mass of 554 grams. Plot these two points on your log-log plot for the dolphins above. Draw a line through the two points and label the line Primates. How do cetaceans compare to primates. If the brain of an 80 kg human followed the trends for primates, what is the predicted brain mass of a human? How does this compare to an 80 kg dolphin? IF intelligence were rated on the basis of brain mass, according to your allometric analyses who is smarter- the 80 kg dolphin or the human?