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460 CHAPTER 10: ADAPTATIONS AND SURVIVAL 10B ADAPTATIONS FOR COLD ENVIRONMENTS In most cases when the water inside an animal freezes, that’s the last we hear of that animal. However, this rule does not apply to the wood frog (Lithobates sylvaticus) of Nort...

460 CHAPTER 10: ADAPTATIONS AND SURVIVAL 10B ADAPTATIONS FOR COLD ENVIRONMENTS In most cases when the water inside an animal freezes, that’s the last we hear of that animal. However, this rule does not apply to the wood frog (Lithobates sylvaticus) of North America. Research suggests that these frogs can survive multiple days exposed to –6 °C in laboratory conditions, and up to seven months at –18 °C in the wild. Even when up to 65% of the water in their body freezes, the frogs are able to survive and thaw out once conditions become warmer whilst remaining completely unharmed. How exactly are these amphibians able to survive such cold conditions, even when the water inside their body literally freezes? Image: Viktor Loki/Shutterstock.com Lesson 10B In this lesson you will learn about how some organisms have developed a set of structural, physiological, and behavioural adaptations to help them survive in cold environments. Prerequisite knowledge Future applications Years 7–10 Year 12 Natural selection acts on the phenotype of an We can determine the genes which convey a organism so that individuals with beneficial phenotypical advantage in one species and, adaptations are fitter and have more offspring. using genetic engineering technologies such as CRISPR, insert these genes into another species Chapter 6 to convey the same phenotypic advantage. Organisms have evolved a variety of thermoregulatory mechanisms to maintain Year 12 homeostasis in cold environments. Hot environments can act as a selection pressure that leads to changes in allele Lesson 10A frequencies of a population. Many of the adaptations to release heat in hot and dry environments are modified to conserve heat in cold environments. Study design dot point structural, physiological, and behavioural adaptations that enhance an organism’s survival and enable life to exist in a wide range of environments Key knowledge units The challenges of cold environments 2.2.5.4 Adapting to the cold: animals 2.2.5.5 Adapting to the cold: plants 2.2.5.6 The challenges of cold environments 2.2.5.4 O VERVIEW The most influential abiotic factor in a cold environment is extremely low temperatures. To help survive in their environment, animals have evolved sets of structural, physiological, and behavioural adaptations, whereas plants have only evolved structural and physiological adaptations. This document is intended for Naomin Lianca JAYAWARDENE at Northcote High School (us er ID: 2762608). Unauthorised circulation in any form is not permitted.  10B THEORY 461 T HEORY DETAILS Many environments experience freezing conditions for part of or all of the year. Even in abiotic factor a property of the Australia, a relatively hot continent, temperatures in our Alpine regions can reach environment relating to non- –23 °C. Much like the hot deserts explored in the previous lesson, cold environments living things. Examples include are exceedingly complex and can be characterised by their abiotic and biotic factors. temperature, nutrient availability, and water availability The most influential factors impacting organisms in cold environments include: biotic factor a property of the low temperature – at low temperatures the reactions required for life slow down environment relating to living or stop. Additionally, water may freeze cell contents and rupture cells. things. Examples include predator- piercing winds – high winds can exert strong pressures and forces on plants, and can prey relationships, competition, dramatically increase the heat lost by an organism. and symbiotic relationships structural adaptation low availability of nutrients – plants absorb nutrients from the soil, and use nutrients evolved modifications to an as the building blocks of macromolecules such as proteins. A lack of nutrients restricts organism’s physical structure macromolecule synthesis and overall growth rate. physiological adaptation precipitation as snow – snow falling instead of rain, and surface water freezing in evolved modifications to an sub-zero temperatures, make it difficult for organisms to obtain the liquid water organism’s internal functioning required for their survival. or metabolic processes Again, much like in deserts, we will explore the set of evolved adaptations in plants and behavioural adaptation animals in response to these four abiotic factors. When considering these adaptations, evolved modifications to an organism’s actions notice that most fall into one of two categories: structural or physiological adaptations. Additionally, animals often possess behavioural adaptations that enable them. Adapting to the cold: animals 2.2.5.5 O VERVIEW Animals have evolved a set of structural, physiological, and behavioural modifications to deal with cold-temperature environments. T HEORY DETAILS convection radiation metabolic heat evaporation conduction Figure 1 It’s just as important to maintain a temperature balance in a cold environment as it is in the desert. In cold environments, organisms evolve adaptations to minimise heat loss via convection, radiation, evaporation, and conduction, and to maximise heat gain. Structural adaptations Animals living in cold environments can have a similar set of structural adaptations to those we observe in desert environments, only now animals are trying to conserve heat rather than release it into the environment. Insulation In cold environments, you will often find animals that have a thick insulating layer covering their entire body. Such insulation is usually composed of thick fur, plumage, or subdermal fat to provide maximum protection against heat release into the environment. Surface area to volume ratio An animal’s surface area to volume ratio can severely impact the rate of heat transfer both into and out of a body. By reducing their surface area to volume ratio, an animal will release heat slowly, increasing the time it takes for body temperature to drop. In cold environments, the more you resemble a sphere (the object with the lowest SA:V ratio), the easier it is to maintain a constant body temperature in a cold environment. This document is intended for Naomin Lianca JAYAWARDENE at Northcote High School (us er ID: 2762608). Unauthorised circulation in any form is not permitted. 462 CHAPTER 10: ADAPTATIONS AND SURVIVAL Image: Mikhail Cheremkin/Shutterstock.com Figure 2 The walrus has a thick layer of insulating fat and a low surface area to volume ratio, reducing unnecessary heat loss in both the aquatic and terrestrial environments. Image: Studio Romantic/Shutterstock.com Figure 3 Which of these two do you think would survive out in the cold for longer? Consider both SA:V and insulation. Physiological adaptations Endotherms versus ectotherms We tend to find a greater proportion of endotherms, rather than ectotherms, in cold environments. This is because animals cannot obtain heat (e.g. via convection, conduction, etc.) from an environment with a lower temperature than their body, so maintaining a stable body temperature via internal metabolic processes is typically advantageous. Given that the body temperature of ectotherms generally matches that of the ambient temperature, cold-adapted ectotherms must be able to tolerate extremely low temperatures. Many cold-adapted animals will burrow underground during the coldest months of the year, where the temperature remains just above freezing. Once the temperature rises during the summer, these animals will return to the surface to feed and breed. Torpor torpor a physiological state in which the metabolism of an animal In lesson 10A, you learned about one kind of torpor, aestivation. There are actually two is reduced to conserve energy other kinds of torpor, hibernation (in endotherms) and brumation (in ectotherms), both hibernation prolonged torpor of which are triggered by seasonal drops in temperature. Hibernation and brumation in response to seasonal cold help an animal survive extended periods in a state of low metabolic activity and body conditions. Occurs in endotherms temperature. A state of torpor is beneficial as the reduction in metabolic rate allows the such as mammals and birds animal to survive on very little food or water, and remaining inactive in shelter allows brumation prolonged torpor animals to avoid harsh weather. in response to seasonal cold conditions. Occurs in ectotherms such as snakes and lizards This document is intended for Naomin Lianca JAYAWARDENE at Northcote High School (us er ID: 2762608). Unauthorised circulation in any form is not permitted.  10B THEORY 463 PYGMY POSSUMS AND THE AUSTRALIAN ALPS The mountain pygmy possum (Burramys parvus) is a tiny marsupial, on average weighing only 40 g, and is the only marsupial restricted entirely to the alpine and subalpine regions of south-eastern Australia. The mountain pygmy possum is one of Australia’s only hibernating marsupials, and they are able to subject themselves to seven months of yearly torpor. During hibernation, mountain pygmy possums burrow beneath a thick layer of insulating snow. In this state their resting metabolic rate drops drastically and their internal body temperature is able to fall as low as 2 oC without causing damage. Once the environmental temperature begins to rise in early spring, the mountain pygmy possum will resurface to feed and breed. The species was known only from fossils and was believed to be extinct until a live individual was discovered on Mount Hotham, Victoria in 1966. Considered critically endangered, only 2 000 of these possums are left in the wild. Challenges faced by the mountain pygmy possum include decreasing habitat ranges due to ski resort construction, global rising temperatures, invasive predators, and a dwindling supply of the possum’s favourite food source, the bogong moth. Image: Gwoeii/Shutterstock.com Figure 4 The mountain pygmy possum, one of Australia’s most critically endangered species Circulation As you learned in lesson 10A, the circulatory system can support a massive amount of heat loss into a desert environment through vasodilation. In a cold environment the circulatory system is equally critical, only here, adaptations to the circulatory system conserve heat rather than releasing it. As blood is pumped out of the heart it is the same temperature as the animal’s core body temperature. If blood of this temperature were to circulate to the peripheries, the temperature gradient between the body and the environment would be quite large, causing lots of heat to be lost. There are two main ways to prevent heat loss from blood: vasoconstriction and countercurrent circulation. The opposite of vasodilation, vasoconstriction, occurs when the diameter of small blood vasoconstriction the narrowing of vessels in the skin and overall blood flow is reduced. When many animals are required blood vessels to conserve heat, the body sends signals to constrict these blood vessels and heat loss is minimised (Figure 5). epidermis heat loss across epidermis air Vasodilation - to release heat Vasoconstriction - to conserve heat Figure 5 Animals can conserve heat by the vasoconstriction of superficial blood vessels. This document is intended for Naomin Lianca JAYAWARDENE at Northcote High School (us er ID: 2762608). Unauthorised circulation in any form is not permitted. 464 CHAPTER 10: ADAPTATIONS AND SURVIVAL Countercurrent circulation techniques use the heat in blood travelling from the heart countercurrent circulation an to heat cool blood returning from the animal’s periphery, meaning that the core body efficient heat transfer method temperature is not lowered. Additionally, this cools the blood heading towards the where separate components of periphery, so the temperature gradient between the periphery and the environment is the circulatory system flow next to each other in opposite directions. reduced and less heat is released to the environment (Figure 6). The combination of both Used to cool blood heading to of these effects means that countercurrent circulation makes it much easier to maintain a the outer surface and heat blood stable core body temperature. heading back to the body’s core periphery the outside surface or boundary of a structure. In an animal, the peripherals refer to structures such as the arms, legs, or skin warm arterial blood In lesson 6B you learned that in response to the cold, cool venous blood humans will shiver to generate heat. Shivering to generate heat is a trait shared by most cool venous blood endothermic animals, and is heat considered a physiological Image: Oleg7799/Shutterstock.com adaptation as it’s initiated after a stimulus-response pathway Figure 6 Marine mammals (such as humpback whales) have evolved countercurrent heat exchange mechanisms to without any behavioural input. reduce heat loss to the environment and maintain a stable core body temperature. Behavioural Reducing exposed surface area Objects with lower surface area to volume ratios release less heat, so many animals will reduce their surface area to volume ratio by hiding or protecting their peripherals as temperatures drop. For instance, in response to the cold many mammals will curl up, and birds may stand on only one leg (Figure 7). Huddling You’ve probably seen emperor penguins huddling during the Antarctic winter, where the temperatures often reach as low as –40 oC. By huddling, animals artificially decrease their individual surface area to volume ratio, decreasing the amount of heat released by the emperor penguin colony into the environment. Image: Diana Leadbetter/Shutterstock.com Figure 7 As their legs have little insulation, birds often stand on only one leg to conserve heat. SA : V = high SA : V = low Figure 8 By huddling, emperor penguins reduce their individual exposed surface area, lowering the average amount of heat lost per penguin in the huddle. Seeking shelter Critically low temperatures and wind chill can quickly drop body temperature, causing permanent damage or even death. By seeking shelter, animals can surround themselves in a stable microclimate with little or no wind and more forgiving temperatures. Animal shelters typically include underground burrows, dens, or rocky outcrops. This document is intended for Naomin Lianca JAYAWARDENE at Northcote High School (us er ID: 2762608). Unauthorised circulation in any form is not permitted.  10B THEORY 465 Image: Elena Birkina/Shutterstock.com Figure 9 Polar bear cub leaving its den in the snow after hibernating for the winter. Migrating to a warmer climate During warmer summer months, alpine regions bloom into areas that are rich in migration the seasonal biodiversity and resources. During winter, however, these same areas are often covered movement of animals from one in a thick layer of snow, making it difficult to access food and water. Rather than adapt to area to another the cold, many animals will simply migrate to a lower altitude or more moderate latitudes where resources are more readily available. Warmer climates are also typically easier for breeding and raising newborns. Image: Paul S. Wolf/Shutterstock.com Figure 10 Humpback whales spend their entire lives migrating around the world to avoid low temperatures, track food sources, and to mate and give birth. Adapting to the cold: plants 2.2.5.6 O VERVIEW Plants have a number of common structural and physiological adaptations which allow In lesson 5B you learned about them to live in the harsh conditions present in a cold climate. the transport of water from the roots to the leaves via T HEORY DETAILS the xylem, and the transport of nutrients around a plant via the phloem. Both of these Visualising the problem: tree lines systems rely on water and, Freezing presents a large and very real stress for alpine and cold-adapted plants, where if that water freezes, neither the barrier between tolerable and intolerable temperatures can be drastic. If you need system can function. This is part of the reason why we proof of this, look at the tree lines in Figures 11 and 12. Low temperatures are the major observe tree lines over a cause of tree lines, although precipitation, wind, and nutrient availability can also play temperature gradient. a role. This document is intended for Naomin Lianca JAYAWARDENE at Northcote High School (us er ID: 2762608). Unauthorised circulation in any form is not permitted. 466 CHAPTER 10: ADAPTATIONS AND SURVIVAL Figure 11 Above this tree line in the Tararua Ranges of New Zealand, the temperature is too low to support large tree growth. Figure 12 In cold air drainage valleys, the temperature on the valley floor can be too low to support large tree growth, making an inverted tree line on the valley floor. Freezing presents a problem for a number of reasons. One is that the enzyme and protein-driven reactions progress slowly at lower temperatures. Additionally, the formation of ice crystals within the cell can rupture cell membranes and other cell contents, and the vascular system of plants cannot transport nutrients when blocked by ice. How to prevent freezing At low temperatures, cell membrane fluidity decreases, which can quickly lead to disruption of the lipid bilayer, decreased membrane protein effectiveness, and cell contents leaking out. To deal with this, many cold-adapted plants modify the lipid and chemical composition of their cell membranes to increase their functioning in low temperatures. The freezing point of distilled water is 0 oC. As the concentration of solutes increases, the lower the freezing point becomes. Plants use this phenomenon to their advantage. When the temperature drops, plant cells receive signals to increase the concentration of solutes such as glucose in their cells, which increases a plant cell’s resistance to freezing. In addition, particular cold-adapted plants can produce antifreeze proteins in response to cold temperatures. These proteins disrupt the formation of ice crystals within the cell, enabling water to remain liquid at lower temperatures. This document is intended for Naomin Lianca JAYAWARDENE at Northcote High School (us er ID: 2762608). Unauthorised circulation in any form is not permitted.  10B THEORY 467 WHY DOES INCREASING THE SOLUTE CONCENTRATION IN WATER DECREASE ITS FREEZING POINT? Materials Ice cubes Table salt (NaCl) Method 1 Freeze two ice cubes. 2 Pour table salt on the first ice cube. 3 Leave the second ice cube alone. 4 Observe the ice cubes for 5 minutes. Questions 1 Describe what happened to the two ice cubes. 2 What was the point of the second ice cube? Explanation When water drops in temperature, individual water molecules lose kinetic energy (or heat), and they begin to condense into a solid lattice structure, or ice. The solid lattice gives ice its rigid feel and appearance (Figure 13a). When you pour salt on the ice, the salt dissolves and individual Na+ and Cl– ions begin to disrupt this lattice structure, and ice becomes liquid water again (Figure 13b). The chemistry term used to describe the lowering of freezing temperature due to the addition of solutes is ‘freezing point depression’. This is why salt is used to de-ice roads in winter. (a) (b) Figure 13 When (a) frozen water molecules arrange themselves in a solid lattice structure they form ice. Dissolved solutes (b) disrupt this lattice structure, lowering the freezing point of water. Deciduous trees A deciduous tree is a tree that seasonally drops all of its leaves at once to avoid harsh conditions. While there are some drought-adapted trees that drop their leaves due to excessive water loss during hot and dry periods, the most common and recognisable deciduous trees are cold-adapted. When compared to evergreen trees, cold-adapted deciduous trees have several advantages: Deciduous trees avoid frozen leaf tissue during winter. Deciduous trees require less energy and water to survive during winter months. Deciduous trees experience less branch breakage during periods of heavy snowfall and strong winds. Image: FotoYakov/Shutterstock.com Figure 14 By dropping all their leaves in winter, deciduous trees are able to avoid damage to leaf tissue, conserve energy and water, and avoid branch breakage due to snowfall and wind. This document is intended for Naomin Lianca JAYAWARDENE at Northcote High School (us er ID: 2762608). Unauthorised circulation in any form is not permitted. 468 CHAPTER 10: ADAPTATIONS AND SURVIVAL Seed dormancy A dormant seed is one that is unable to germinate during a specific time under certain environmental conditions. Seed dormancy is a trait of many cold-adapted plants, where seeds will be dispersed before the winter months, and then remain dormant until warmer spring weather. When the seeds detect increases in temperature or light availability, they quickly sprout and grow during the favourable living conditions of the summer months. CUSHION PLANTS Many alpine regions appear little more than barren rocky outcrops, littered here or there with a few round ‘cushions’ of grass. However, these little cushions, known as cushion plants, are far more complex and interesting than you might initially expect. Each individual cushion plant is often a tight knit community of similar, yet completely individual, species. These species work together to form a complex net facing outwards towards the environment, reducing the exposed surface area of individual leaves and providing resistance to wind and snow. The cushion plant has a hollow interior which is separated from the harsh environment and warmed by the metabolic activities and stored heat of the plant, providing resilience to freezing. (a) (b) Figure 15 From afar, (a) you might mistake cushion plants for regular moss but upon closer inspection you would realise (b) that each plant is actually a tight knit community of many different species. Both pictures show cushion plant communities found near Cradle mountain, Tasmania. ANTIFREEZE PROTEINS IN PLANTS AND FISH Plants can prevent freezing by producing antifreeze proteins, but did you know that some fish can do the same thing? Because of their high salt content, oceans of the Antarctic remain liquid at down to –1.9°C. But these waters are still populated by ectothermic fish, such as the notothenioids, whose bodies resist freezing in the frigid conditions. They do this by producing similar antifreeze proteins as plants, preventing the formation of large ice crystals in the body. These antifreeze proteins are limited not only to plants and animals, however, and similar proteins have been found in every other kingdom of life. Figure 16 The emerald rockcod (Trematomus bernacchii) This document is intended for Naomin Lianca JAYAWARDENE at Northcote High School (us er ID: 2762608). Unauthorised circulation in any form is not permitted.  10B THEORY 469 Theory summary A cold environment poses just as many challenges as a hot one, but many organisms thrive there despite the harshness. These organisms have evolved interesting and efficient structural, physiological, and behavioural adaptations to deal with tough and unique abiotic challenges associated with a cold environment. While the strategies to maintain balance are as numerous as there are cold-adapted species, there are common strategies that many animals and plants have adopted. Table 1 Some structural, physiological, and behavioural adaptations of animals and plants to survive in cold environments Animals Structural adaptations Insulation techniques Decreased surface area to volume ratio (SA:V) Physiological adaptations Endotherms versus ectotherms Vasoconstriction of peripheral blood vessels Countercurrent circulation Torpor Antifreeze proteins Behavioural adaptations Reducing exposed surface area Huddling Seeking shelter Migration Plants Structural and physiological Modifications to the cell membrane adaptations Increasing solute concentration (freezing point depression) Seed dormancy Antifreeze proteins Even though 65% of the water in the wood frog (Lithobates sylvaticus) freezes, it’s all about where the water freezes, not how much water freezes. When wood frogs sense steep temperature drops they accumulate urea and glucose inside their cells to concentrations much greater than normal conditions. They also begin producing specific antifreeze proteins that accumulate within their cells. This massively reduces the freezing temperature due to freezing point depression, ensuring that intracellular tissue remains liquid at low temperatures. However, the concentration of urea and glucose in the extracellular liquid is not greatly increased and while these fluids may freeze, ice crystals in these regions do relatively little damage. When the environmental temperatures rise naturally, this extracellular fluid unfreezes and the frog can get back to its business. This document is intended for Naomin Lianca JAYAWARDENE at Northcote High School (us er ID: 2762608). Unauthorised circulation in any form is not permitted.