Investigate about thermoregulation of marine mammals

ENVI 121: Marine Mammal Insulation Lab

Goals for Today’s Lab:
• To investigate the thermoregulation of marine mammals by performing an insulation experiment

Marine reptiles, birds, and mammals all have terrestrial counterparts from which they differ morphologically and physiologically in order to survive in the ocean. This lab will explore morphological characteristics and will focus specifically on thermoregulation, or how some marine organisms have overcome the thermal challenges of a marine existence. Because water has a high heat capacity (the rate at which energy is transferred down a temperature gradient), it steals heat from a warm body approximately 25 times faster than air of the same temperature. This high heat capacity means that living in the ocean presents a challenge for endothermic homeotherms (i.e., “warm-blooded animals”), such as marine birds and mammals, which produce metabolic heat to maintain their stable high core body temperatures. However, living in the ocean is also challenging for ectothermic poikilotherms (i.e., “cold-blooded animals”), such as marine reptiles, which have body temperatures that reflect their surrounding environment, which become inactive when exposed to cold temperatures for prolonged periods, and which rely on external heat sources such as the sun to increase their body temperatures.

It is most energetically efficient for marine mammals to remain in their thermoneutral zones. Different marine mammals have evolved different strategies for a marine existence.

Blubber
All cetaceans (whales and dolphins) and pinnipeds have a blubber layer, which is a layer of fat just under the skin. Blubber has a low thermal conductivity and requires little blood to maintain, so heat transfer to the environment through a blubber layer is minimal. In cetaceans and pinnipeds that live in cold water, the blubber layer is thick, and blood flow to the blubber is restricted. Cetaceans and pinnipeds that live in warmer water, or those that haul out in warm areas, can “reduce” the thickness of their blubber layers by increasing blood flow through the blubber, which “decreases” the thickness of the insulating layer and allows heat loss to the environment.

Counter-current heat exchange
Marine mammals (and birds) have appendages that are not insulated by blubber or feathers. Specific arrangements of arteries and veins in these extremities can help conserve heat in cold surroundings, and can facilitate heat loss in warm surroundings. In these poorly-insulated extremities, arteries carrying warm blood away from the heart are completely surrounded by a series of veins carrying cooled blood from the extremities. Heat from the arterial blood is transferred to the cool venous blood (down its temperature gradient) as it flows in the opposite direction back to the heart. That way, heat is conserved within the core of the animal, and arterial blood reaching the extremities is already cooled, whereas venous blood reaching the heart is already warm.

Fur
Only one marine mammal, the sea otter, relies entirely on fur for insulation. Otters have the densest fur of any marine mammal; each inch of their bodies may be covered by up to one million hairs (we have approximately 80,000 hairs on our entire bodies). Their coat is composed of waterproof guard hairs on the surface and a short underfur layer beneath, and is so dense that it can’t be parted in order to see the skin beneath. Otters groom for a large proportion of their time; grooming entails blowing air into their underfur layer, creating an air layer between the water and their skin. When they are floating on the surface, their skin is never wet. However, when they dive to forage, the increasing pressure compresses their coat; air bubble streams are often seen coming from behind diving otters. Diving reduces the insulative qualities of otter fur, and otters must groom again immediately upon surfacing in order to reestablish their air layer. Because they are so reliant on their fur for survival, otters can’t molt they way other marine mammals, such as seals and sea lions, can. Instead, they continually shed and re-grow hair. Sea otters also have a high metabolic rate as an additional adaptation for maintaining a high body temperature in a cold environment. To fuel their high metabolic rate, otters consume a large number of calories everyday relative to their body size.

Polar bears and fur seals also have fur with insulative qualities. Fur seals spend a good deal of time grooming as well, but both fur seals and polar bears have blubber to aid in thermoregulation.

Body Size
Endotherms in cold environments have evolved larger body sizes as a mechanism to retain metabolic heat. Large body size is also an adaptation for terrestrial animals in very hot environments as a way to reduce overheating. Large animals have a small surface-area-to-volume ratio relative to small animals. The small ratio means that there is less surface across which to lose heat to the environment, and more volume in which to hold heat in.

Methods
1. Fill the plastic tub with ice and cold water. Let it chill for approximately five minutes.
2. Take the temperature of the ice bath (oC) and record in your lab notebook
3. Let the tap water run until it is as hot as possible and then fill a beaker
4. Take the temperature of the water in the beaker and record this temperature in your lab notebook. This is your initial temperature (assume that the water you fill your balloon with is the same temperature). Dump out the water.
5. Fill the balloon with the same hot water from the tap (sometimes it’s easier to fill the balloons if you blow them up and deflate them first). Fill each balloon with approximately 300 ml of water, and then twist the top of the balloon and secure it with a binder clip. To do this, fill a large (1 l) beaker with water up to the 400 ml mark. Then place your secured, filled balloon in the beaker. You want your balloon to displace 300 ml of water, so you want the water level in the big beaker to go up to 700 ml. Adjust the water in your balloon accordingly. You want to control for balloon size, because large size is an adaptation for retaining heat.
6. Add your group’s form of insulation to the balloon (see instructions below).
7. Repeat steps 5 and 6 two more times, so that your group makes a total of three balloons.
8. Immerse the balloons in the ice water for five minutes.
9. After five minutes, remove the balloons from the ice water.
10. CAREFULLY remove the binder clips and empty the water in the balloons back into separate beakers.
11. Take the temperature of the water in each beaker and record in your lab notebook.
12. Calculate the heat lost in each balloon by subtracting the final temperature of each balloon from the initial temperature.
13. Calculate a mean and standard deviation for amount of heat lost for your form of
insulation.
14. Record the mean and standard deviation for your group in the Excel spreadsheet on the lab’s computer.
15. The data will be emailed to you, and you will make bar graphs of the results.

Control
Follow the directions above, and skip step 6.

Fur
Fur works as an insulator for marine mammals only when it traps an air layer between the water and the animal’s skin. You will need to place one balloon inside another balloon, and fill up the inside balloon with water and the outside balloon with air. Then you will add insulation to the outermost balloon.
1. Follow the directions above for steps 1-4.
2. Using a pencil, insert the ERASER end all the way into the end of a balloon.
3. Holding the first balloon tight around the pencil, take another balloon and roll it onto the pencil on top of the other balloon.
4. Carefully remove the pencil, making sure that you don’t accidentally pull the first balloon out of the second balloon.
5. Fill the INSIDE balloon only with the hot tap water.
6. Twist the top of the inside balloon and secure it with a binder clip.
7. Blow up the outside balloon so that the inside water balloon is completely surrounded by air. This can be tricky, and inserting a drinking straw into the outside balloon may help you to inflate it (blow air through the straw, and then trap the air inside by pinching the balloon closed as you remove the straw).
8. Secure the outside balloon with another binder clip, and then follow the directions above from step 8.
Blubber
You will use Crisco for your blubber layer.
1. Follow the directions above for steps 1-5.
2. On a desk or table, lay out a sheet of Saran wrap that’s big enough to entirely cover a full water balloon.
3. Using the back of a plastic spoon, spread approximately a ¼-inch thick layer of Crisco out on the Saran wrap.
4. Fill your balloons with hot water according to the methods above.
5. Wrap each balloon in a Crisco blubber layer, making sure the whole balloon is
covered.
6. Follow the directions above from step 8.

Fur and Blubber
Follow the directions above for steps 1-4. You will need to make “fur” balloons according the fur directions above. Make your air layers fairly thin. Then, wrap your outer air balloons in thin layers of Crisco (approximately 1/8-inch thick). Then, wrap your balloons in insulation, and follow the directions above from step 8.