[MUSIC] Like the plants we discussed in the last lesson, animals also have to cope with cold temperatures, intense solar radiation, long winters, short summers, and thin air. Animals living in the mountains have evolved special adaptations that increase their survival and reproduction in these environments. These adaptations may be morphological, behavioral, or physiological. And species have usually adopted some combination of all three types of strategies. Let's take a closer look. Animals need to be able to maintain their internal temperatures despite dramatic changes in ambient environmental temperature. If body temperature goes outside of an acceptable range, enzymes in cells will not be able to perform chemical reactions. And if the contents of a cell freeze, ice crystals can form inside the cell which will damage cellular structures. So, regulating body temperature is really important. The process that allows animals to maintain body temperature is called thermoregulation. It's controlled by a negative feedback system, similar to how a thermostat works. If nerve cells detect shifts in body temperature outside of the normal range, they send a message to the brain to initiate a corrective response. Thermoregulation is achieved in different ways by ectotherms and endotherms. Ectotherms are animals that primarily regulate their temperatures using external sources of heat. Endotherms create most of their heat from metabolic processes. Mammals and birds are typically endothermic, while amphibians, reptiles, fish, and invertebrates, are ectothermic. When you think of cold adaptation in animals, one obvious strategy that comes to mind is fur and feathers. Hair and feathers insulate animals by trapping a blanket of warm air near the skin, and hollow hairs or feathers can amplify this effect. Just like pubescence on plants, fur and feathers act as insulation to retain heat and reduce convective cooling. [SOUND] Many animals in the alpine also have lower surface area relative to their mass, giving them a stocky appearance. A smaller surface area helps animals retain body heat. They're recognizable by their short appendages relative to similar animals adapted to lower elevations. For example, pikas are small lagomorphs that are most closely related to rabbits and hares. Pikas live high in the mountains of Asia and North America, and they have very reduced ears and limbs compared to their low elevation cousins. However, for some smaller alpine-dwelling animals, it may be advantageous to have an increased surface area. For example, the wing size of flying insects is often proportionally greater in high altitude populations so they can cope with the thinner air encountered during flight. For actively flying insects, wing loading will be higher at greater elevations, so these populations are subjected to stronger selection for wings with an increased surface area. For example, in males of the fly, Drosophila flavopilosa, in Chile, both wing length and breadth are increased with elevation. Finally, some alpine animals have darker coloration at higher elevations in order to absorb more solar radiative heat. This warms their flight muscles. For ectothermic insects, it can be advantageous to adjust body temperature through thermal basking and by selection for specific spectral reflectance and absorbance properties of the body surface. Essentially, these alpine species are reducing their albedo. Perhaps the best examples of this adaptation strategy are alpine butterflies of the genus, Colias, or the sulphur butterflies. In Colias, this melanization is essential for thermal regulation, because darker wings absorb more sunlight. By basking in the sun, butterflies can raise their body temperatures sufficiently to allow flight. In one species of Colias from the Rocky Mountains of Colorado, the degree of wing melanization increased tenfold between 1,800 and 3,000 meters. Similar altitude-related color polymorphism, or morphological variation, is seen in other insects as well, including leafhoppers, ladybirds, and grasshoppers. Museum collections are essential for conducting research on biodiversity, phylogeography, and adaptations of species to different environments. Here is Dr. Felix Sperling, curator of the EH Strickland Entomological Museum at the University of Alberta, to introduce us to some alpine butterflies. >> Butterflies are very charismatic, partly because they are nice and furry in the mountains. And so one of the things that you notice if you look at a butterfly like this, these are two specimens of the same species. One of them is from the mountains, and it has a beautiful furry body. And it has shorter, stumpier wings. It's a little bit darker. And this one comes from grasslands not very far away. And it's sleek, and it's thin, and it has hardly any hair. Of course, being hairy is very nice when you are cold. It keeps what little heat you might have gained from dissipating away. And hair is not the same as in mammals, but it functions the same way. Pigmentation really works nicely if you are dark and you have a little bit of sun, and that can warm you up beautifully. It comes at a potential cost, but I'll give you an example here. Here is one butterfly that happens to have quite a dark underside. And many of them rest with their undersides showing. And another one that is just a little bit lighter, but it makes a difference to that specimen. And they can be part of the same population in not heating up as fast. And so the ones that are darker tend to be found higher up in the mountain where it's a bit cooler. And the ones that are lighter are further down where there's actually a cost sometimes to heating up too much. Climate change has a lot of effects on butterflies. It affects their distributions, because some of the butterflies that were found further south in the mountains, in the Rockies, are no longer found there. And they're now found more frequently further north. Climate change, I would expect, will also have changes in the distribution within a mountain. You're going to found a particular, especially dark and hairy butterflies found higher up on the mountain. And, of course, there is always the danger that they get squeezed off the top of the mountain and that's the end of them. The Strickland Museum of Entomology has almost a 100 year history now. And that means it contains a huge amount of information that you just can't get with a basic ecological study. Because here are specimens that people have collected, and a lot of places that you can still get access to decades later. And it's easy to document that there are real changes that have happened during that time. Collections like this also are really good for showing a great variety of specimens and species that you can do phylogenetic analyses on. And that can give you access to deep time, to time in the order of hundreds of thousands, millions of years, that can show major climate changes. And even mountains rising up in places that they weren't there before. >> Behavioral adaptation concerns hour-to-hour, day-to-day, and even seasonal choices made by animals that actively contribute to temperature regulation. Ectotherms are very capable of surviving at a range of temperatures. But since they're not able to regulate their internal heat production, they rely on behavioral adaptations to keep their temperatures within their normal range. Ectotherms rely on external production of heat. So they often have periods of inactivity that are correlated with cooler temperatures. When their internal temperature drops, their enzymes become less effective and their metabolism decreases. Small ectotherms that are highly susceptible to heat loss, due to their relatively large surface area, rely heavily on microclimates to survive the harsh alpine conditions. For example, recall that the interior of cushion plants are often favorable microclimates that can host a variety of invertebrate species. And pollinators may be found seeking refuge from the cold inside flowers. One species of rock-dwelling lizard in the genus, Phymaturus, that thrives at elevations above 4,000 meters in the Andes, is a good example of how animals can use behavioral responses to adapt to cold temperatures. At night, the lizard burrows underground where the soil provides insulation from cold nights. In the morning, the lizard emerges from it's burrow and generates heat by basking in the sun, which can increase its internal temperature to 30 degrees Celsius, even if ambient temperatures are around freezing. Extreme low temperatures during winter are also a challenge for endothermic organisms in alpine regions. Some animals opt to avoid them all together by moving to less exposed areas. Large mammals, such as big horn sheep, migrate to lower elevations during the winters, while birds migrate to lower latitudes. Small alpine animals migrate less frequently, because this would require relatively high energy expenditure. However, movement over shorter distances between microclimates can be a remarkably effective way for animals to thermoregulate. The collared pika, Ochotona collaris, lives in the mountains of Yukon and Alaska. Colored pikas minimize their exposure to extreme ambient temperatures by seeking shelter in piles of boulders adjacent to alpine meadows. Boulders provide protection from the sun, rain, wind, and fluctuations in air temperature. In both summer and winter, pikas use these sheltered places to help maintain their own thermal equilibrium. In contrast to behavioral and morphological adaptations, physiological adaptations are involuntary, passive responses that are internally regulated. Physiological adaptations that are used to warm animals can be categorized into two groups. The first involves heat conservation, while the second involves heat generation. First, let's consider three different physiological adaptations in alpine animals that reduce the rate at which they lose heat to the environment. One way animals can conserve heat is by raising their fur to increase the barrier of warm air that provides insulation. This reaction, called piloerection, is an involuntary reflex caused by muscle contractions near the surface of the skin. Piloerection may seem like a small thing, but it can be very effective. In fact, despite having lost most of the hair that covered our ancestors, the involuntary response is still present in humans and is what produces goosebumps. Secondly, at low temperatures, blood vessels near the skin decrease in diameter in a process called vasoconstriction. By reducing the amount of heat brought to the surface of the body, vasoconstriction restricts heat transfer to the environment. Vasoconstriction is the reason that people appear pale when they're cold. The third physiological adaptation that helps alpine animals conserve heat is countercurrent heat exchange. This adaptation involves a special arrangement in the circulatory system whereby arteries that carry warm blood to the extremities run parallel and in close proximity to veins that return blood to the trunk of the body. The temperature gradient created by the countercurrent flow causes heat in arterial blood to be progressively transferred to cooler venous blood. This means that arterial blood is substantially cooler when it reaches the body's extremities, so less heat is lost to the environment. All organism produce heat as a byproduct of metabolism, but endotherms have adaptations that amplify their internal heat production under cold conditions in a process called thermogenesis. One way that thermogenesis can occur is through shivering, produced by small involuntary contractions of skeletal muscles. Shivering is both common in both birds and mammals. In contrast, non-shivering thermogenesis involves the release of a hormone that increases an animal's metabolic rate and is found mostly in mammals. Although non-shivering thermogenesis can take place throughout the body, alpine species, especially those that hibernate, often have a tissue called brown fat that's specialized for heat generation. Brown fat stores are an important source of heat during periods of hibernation. Many animals spend the short summers at high elevations gathering energy and resources to build up insulating fat that allows them to survive the winter. Increased insulation can also be achieved by growing additional layers of hair or feathers, or seeking shelter in burrows. Hibernation is an adaptation that saves animals energy by reducing their activity levels. Hibernation is a type of long term torpor, which is a state of low metabolic rate and decreased body temperature. During hibernation the heart rate and breathing is substantially reduced. For example, a marmot's heart rate drops from 180 to 200 beats per minute, to only 28 to 38 beats per minute during hibernation. And their respiratory rate decreases from 60 breaths per minute to 1 to 2 breaths per minute. Hibernation is not the same as hypothermia, because hibernating animals readjust their set point for temperature, essentially establishing a new lower temperature limit. Temperature continues to be regulated by a negative feedback system so that if the temperature drops below the set point, thermogenesis is initiated. Ectotherms can't hibernate in the same way, but many species are capable of over-wintering under extreme conditions. Some insects that live at high elevations adapt to cold temperatures using supercooling, a process where water cools below its freezing point without changing phase into a solid. Remarkably, without a source for nucleation or forming crystals, water can cool to below minus 40 degrees Celsius without freezing. Some species produce unique carbohydrates and amino acids before winter, which helps prevent their cells from freezing. One of those carbohydrates, propylene glycol, is the same chemical used in automotive antifreeze. These cryoprotectants protect tissues from freezing and can prevent some of the adverse effects of extreme low temperatures. Other species are considered freezing tolerant and can survive ice formation within their tissues. One example of this strategy is the New Zealand alpine cockroach, Celatoblatta quinquemaculata. These cold-adapted cockroaches can survive freezing down to about minus six degrees Celsius. However, lower temperatures are lethal. Alpine animals not only have adaptations to survive cold winters, but they also have adaptations that enable them to thermoregulate during warm summers. Animals can dissipate heat through heat exchange surfaces and evaporative cooling. Heat exchange surfaces accelerate heat loss through specialized appendages, like ears. These appendages facilitate the transfer of heat from the animal to the environment because they have a high surface area with many blood vessels close to the surface, and are often only lightly insulated. Although alpine animals have heat exchange surfaces, the relative surface areas of these appendages tends to be smaller than those of animals in warmer environments. Because large heat exchange surfaces would detrimentally affect their ability to retain heat, evaporative cooling can help animals keep cool through the evaporation of water from the body. This can be accomplished either through sweating or panting. Sweating is a passive process relying on air currents to remove water secreted by sweat glands onto the skin. Panting is an active process in which animals produce air currents to remove water across respiratory system surfaces. So far, we have mostly considered ways in which alpine animals have adapted to temperature extremes. But alpine animals have also adapted to other environmental conditions in mountains, including unstable terrain, unproductive habitats, and low oxygen levels. Many mountain dwelling animals, including mountain goat and yak, have specialized hooves that allow them to safely and efficiently navigate steep and rocky mountain terrain. These hooves combine a hard outer edge with a soft inner pad that provides cushioning for jumping between rocks. The structure of the hooves helps animals grip rocks and resist slipping. Mountain animals have adapted to the unproductive nature of their terrain where food supplies are sparse. For example, mountain sheep and yak, like other ungulates, have a multi-chambered stomach that allows them to increase the amount of nutrients extracted from the hard, dry vegetation that forms their diet. As a result, they can eat almost any type of vegetation, reducing the amount of time spent searching for food. Some species can also consume large amounts of vegetation quickly, and then retreat to protected areas away from predators where they can safely re-chew and digest their food. Many alpine animals also have unique adaptations that allow them to survive low oxygen levels at high elevations. They tend to have large hearts and lungs, and more blood cells to carry oxygen. For example, llamas in the Andes are exceptionally well adapted to living in the alpine. They have the highest concentration of red blood cells of all mammals, and the process of binding and transporting oxygen in their blood, using hemoglobin, is very efficient.
