On the plane a few weeks ago, I was watching the "Coastal Seas" episode of the Blue Planet series, and they mentioned ways in which warm blooded animals maintain their body temperature while living in such cold habitats, such as the Arctic and Antarctic Oceans. Then in my General Biology class, we have been learning about homeostasis and how animals physiologically maintain a balance within their bodies. Since a good amount of information from both sources overlap, I am going to describe those animals through what I have learned from both experiences.
Walruses, when they first emerge on land to breed every year, their skin is a ghostly white. This is because they are warm blooded animals, and to conserve heat in a very cold ocean, must keep their blood concentrated in the core of their bodies. On land their outer vessels dilate, which turns their skin from white to pink. Then they can molt their skin by rubbing themselves against rocks, and no longer need to expend energy maintaining their body tempterature. In fact, conserving heat may be the main reason why so many sea dwelling mammals are forced to return to land each year.
Elephant seals have really big noses (as you can see by the sketch of mine I have provided for you below), and I wondered why. Perhaps it serves to increase surface area within the nasal canal so the seal loses less heat and moisture to the surrounding environment. The elephant seal does live in the Antarctic Ocean, the coldest ocean in the world, so maintaining its body temperature would be a crucial aspect of its daily life.
Not just in large nosed animals such as elephant seals, but with all endotherms (or animals which regulate their body temperature by producing heat metabolically or by using active mechanisms of heat loss), heat exchangers in the nasal passages are an excellent way to conserve both heat and moisture. During inspiration --while breathing in--, the air is warmed and saturated with water by evaporating water from the nose. Incoming air is warmed and humidified, thus cooling the nose. During expiration --while breathing out--, air is cool and loses water by condensation, which wets the nasal passage. Outgoing air is cooled and loses water, wetting the nose.
Thus, you regain some of the water and heat that you lost when exhaling. However, it is not perfect because you will always lose some heat and water. Some water is recovered during exhalation by condensation on the cool surfaces of the nasal mucosa. Therefore, the longer and thinner the nasal passages, the more recovery. This would explain why elephant seals have such large nasal passages, but the fact that only the males have such large noses suggests there is sexual appeal behind that large nose, such as a bird's bright plumage or a lion's mane.
Lizards of the Sea: Galapagos Marine Iguana
Cape Douglas in the West Galapagos is completely unprotected from the massive waves of the Pacific Ocean and is one of the roughest coasts in the world. The marine iguanas that live there are the only sea faring lizards, and they only eat seaweed.
The local crabs over time have become flattened, which minimizes the effect of the waves on their balance. The iguanas have also adapted, but instead of shells they sport huge claws to grip to the rocks. Their diet is the ultimate "fast food", since they only have a few seconds to take a few mouthfuls of seaweed before the next breaker comes pounding in.
While the females only feed on the rocks, the males will sometimes swim and dive to reach the weed. He can go as deep as ten meters, which is a desirable ability since there beyond the destructive waves are the best stores of seaweed. However, still being cold blooded, they need to return to land within ten minutes or so to warm up again in the sun. The males are bigger and thus more able to conserve their body temperature for a longer period of time, which might explain why only the males dive for food but not the smaller females.
Some ectotherms (animals whose body temperature are determined primarily by external sources of heat), such as the marine iguana, regulate the blood flow to the skin. The Galapagos marine iguanas do this in order to alter their heating and cooling rates. As soon as the iguana enters the ocean, it begins to cool and its heart rate drops rapidly when it is cooling. However, when it leaves the ocean to bask on the hot rocks, the iguana's heart rate rises rapidly. The rate at which the iguana's body temperature warms is greater than the rate at which it cools, which is highly beneficial because it means the lizard can function for longer bouts of time under the waves and will have a shorter time needed for recovery between those bouts.
The control of blood flow to the skin can be an important adaptation for an ectotherm such as the marine iguana (a reptile) of the Galapagos archipelago. The Galapagos are volcanic islands that lie on the equator but are bathed by cold ocean currents. The iguanas bask on hot black lava rocks on the shore, then enter the cold ocean water to feed on seaweed. When the iguanas are feeding, they cool to the temperature of the sea. This cooling lowers their metabolism, making them slower, more vulnerable to predators, and incapable of efficient digestion. They therefore alternate between feeding in the cold sea and basking on the hot rocks. It is advantageous for iguanas to retain body heat as long as possible when basking. They can accomplish these changes in heat transfer rates by changing their heart rate and the rate of blood flow to their skin.
I did not take this picture, but found it on a Google Image search for "marine iguana". I chose this one because I liked how it showed the iguana basking with its head up high to increase the impact sunlight has on its body, and it included the local crabs and water in the background.
As a side note, just because I find these Galapagos marine iguanas so interesting, since the rocky shore is unsuitable to lay their eggs, the iguanas must journey inland to find a more suitable spot. The females lay their eggs in burrows to hatch from, and so they need soft sand. Although it is easy to escape danger in rocky crevices on the shore, on open sand inland they are extremely exposed to predators. Even so, if caught in the unrelenting talons of a Galapagos hawk, these lizards won't give up without a struggle.
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