BIO270 Laboratory Guide #3
DEVELOPMENT; ALLOMETRY;
BONE METRICS; JOINT MECHANICS
After completing this laboratory you should be able to:
1) List the major stages in vertebrate embryological development and understand the progressive changes that define each stage transition;
2) Identify the specific structures in Part I below;
3) Understand the concept of allometry as it applies to comparative studies of development and phylogeny;
4) Understand how and why body proportions are not size-invariant;
5) Be able to calculate measures of mechanical advantage across joints and relate those to animal design and function.
I. VERTEBRATE DEVELOPMENT
1) Work through the "Chickscope" website via the link to the left. This has well-labeled photomicrographs of chicken development in ovo and will give you a broad understanding of the stages of development from production of the egg to hatching at day 21.
2) Work through the sample slides of chick early embryogenesis. Be able to identify the structures in the list below. You can use the accompanying cards and the labeled photographs in Chickscope as guides.
Structures to identify:
15-18 hours:
primitive streak
48 hours:
same structures as 33 hours
otic vesicle (ear)
foregut
24 hours:
head
foregut
notochord
neural groove/neural tube
72 hours:
same structures as 48 hours
telencephalon and diencephalon
medulla oblongata
aortic arch
forelimb (wing) buds
hindling (leg) buds
33 hours:
brain vesicles
prosencephalon
mesencephalon
rhombencephalon
optic vesicle
heart
neural tube/spinal cord
somites
vitelline vessels
96 hours:
same structures as 72 hours
olfactory pit
crystalline lens in eye
ventricle in heart
allantois
tail
II. ALLOMETRY - DEVELOPMENT
1) Choose either the set of three human skull models (infant, juvenile, adult) or the comparable set of three alligator skulls.
2) Establish a set of 10 landmarks bilaterally on the adult skull. Make sure that for each of these you can find the homologous point on the juvenile skull. Also make sure that these landmarks span the upper, lower, rostral, caudal, medial and lateral surfaces of the skull, the areas of the eye sockets, snout, and jaw hinges, and the mandible (lower jaw). Use the Meers article or the Wu link at the left for a guide to some useful landmarks for the alligator.
3) Mark each landmark or pair of landmarks (right and left) on the adult skull with a green label and number or letter them in some logical order for identification.
4) Using your 10 landmarks, come up with a set of ~15 point-to-point distances. Some distances should be rostro-caudal, some should be medio-lateral, some should be dorso-ventral and some should be contralateral between homologous points. Again, make sure that your chosen distances cover the entire skull. The Meers article may provide some good examples.
5) Use the calipers and/or flexible rulers to measure this set of ~15 distances on both the adult and juvenile skulls. Record these numbers. For each distance calculate a proportional growth rate as the ratio of adult length/juvenile length.
6) Based on these measures, which areas seem to have the highest proportional growth rates? In other words, as the skull grows, which areas stretch out and which diminish in relative size? How does this relate to ecological differences between adults and juveniles?
7) Use a few measures on the infant alligator skull (on the alligator skeleton) or the fetal human skull model to confirm or deny that relative differences in growth rates for different regions of the skull are approximately constant during the early life of the alligator.
III. ALLOMETRY - ADAPTIVE RADIATION/DOMESTICATION
1) Domestication - Work with the set of dog skulls (coyote, shepherd, minipin, other) or cat skulls (tiger, bobcat, domestic cat).
2) Establish the same set of 10 landmarks bilaterally on each skull. Make sure that for each of these you can find the homologous point on the terrier skull. Make sure that these landmarks span the upper, lower, rostral, caudal, medial and lateral surfaces of the skull, as well as the areas of the eye sockets, snout, and jaw hinges.
3) Mark each landmark or pair of landmarks (right and left) on each skull with a green label and number or letter them in some logical order for identification.
4) Using your 10 landmarks, come up with a set of ~15 point-to-point distances. Some distances should be rostro-caudal, some should be medio-lateral, some should be dorso-ventral and some should be contralateral between homologous points. Again, make sure that your chosen distances cover the entire skull.
5) Use the calipers to measure this set of ~15 distances on each skull. Record these numbers.
6) Based on these measures, which features seem to have been selected for in the dog domestication process? Which features have diminished in relative size? How does this relate to the domestication process and artificial selection pressures?
7) What features increase in relative size and which decrease as you compared the tiger (Pantera tigris - one of four "great" cats) to the bobcat (Lynx/Felis rufus- one of the "lesser" cats), then to the domestic cat (Felis sylvestris cattus)? How does this relate to ecological differences, such as prey choice?
IV. BONE METRICS
This part of the lab will look at the relationship between organism size and robustness. As discussed in class, if the size of an organism were simply scaled up two-fold, the mass of the organism should increase proportional to the volume, or approximately 8-fold (23). At the same time the load-bearing capacity of the long bones would only increase proportional to their cross-sectional area, or approximately 4-fold (22). Thus, for closely-related animals, larger animals should tend to be more robust.
A) Bullfrog (Rana catesbiana) bones
1) Using the digital calipers provided, work with your group to measure carefully each of the following on each of the bullfrog skeletons provided:
femur
length
minimal shaft diameter
tibia
length
minimal shaft diameter
humerus
length
minimal shaft diameter
2) Accumulate your results on a spreadsheet.
3) For each bone (femur, tibia, humerus) produce a scatterplot of minimal shaft diameter as a function of length.
4) Do your results conform to the prediction that larger animals tend to be more robust?
B) Rodent bones
1) To obtain an "economy" set of closely related rodents of varying sizes you will dissect their bones from owl pellets.
2) Work with your group to dissect your owl pellets and identify all of the skeletal remains.
3) Isolate the rodent femur, tibia, and humerus bones for your group. Use only those bones which are completely intact for this study.
4) Measure carefully the following on each of your bones:
femur
length
ball diameter
minimal shaft diameter
tibia
length
minimal shaft diameter
width of proximal head
humerus
length
minimal shaft diameter
width of humeral flange
5) Combine your results with those of your classmates in the class spreadsheet.
6) For each bone (femur, tibia, humerus) produce a scatterplot of each of the other variables as a function of length.
7) Do any of these comparisons conform to the prediction that larger animals tend to be more robust?
V. JOINT MECHANICS
1. On each of the representative vertebrate skeletons (goat, rat, mole rat, mole, cat, rabbit, human, alligator) measure and calculate the following:
forelimb
olecranon to elbow pivot distance = Li(e)
elbow pivot to distal end of toes = Lo(e)
forearm mechanical advantage = A(f) = Li(f)/Lo(f)
hindlimb
point of calcaneous to ankle pivot distance = Li(h)
ankle pivot to distal end of toes = Lo(h)
heel mechanical advantage = A(h) = Li(h)/Lo(h)
2. Considering Li and Lo to be the input and output lever arms across each joint, how does the mechanical advantage A relate to power? To speed?
3. For each animal, is the mechanical advantage higher across the elbow, forearm, wrist, and manus (hand) or across the heel and pes (foot) ? How does this relate to the mode of locomotion of the animal?
4. How do A(f) and A(h) compare across species? How does this relate to the ecology of these animals?
