Bio II lecture Chapter 40 Basic Principles of Animal Form and Function

Diverse Forms and Common Challenges

Desert Ant Adaptations

• Species Overview: The desert ant, belonging to the genus Cataglyphis, is a remarkable insect known for its extraordinary adaptations to extreme desert environments.

• Foraging Behavior: These ants are known to forage during the hottest parts of the day, often enduring temperatures above 60°C (140°F). This behavior not only showcases their resilience but also highlights their unique adaptations to survive in harsh climates.

• Anatomical Adaptation: One of the key anatomical adaptations is their long stilt-like legs, which elevate their bodies above the hot ground. This adaptation helps lower their body temperature by approximately 6°C compared to ground level, reducing heat absorption.

• Speed and Foraging Strategy: The desert ant can reach speeds of up to 1 meter per second, which is crucial for minimizing sun exposure during their foraging activities, allowing them to gather resources efficiently while avoiding overheating.

Natural Selection and Adaptation

• Natural Selection Mechanisms: Natural selection operates by favoring variations that enhance an organism's relative fitness, improving their survival prospects in challenging environments.

• Importance of Adaptations: In the context of desert ants, the shape and function of their legs exemplify how adaptations are crucial for survival. Such morphological traits directly relate to their ability to withstand extreme environmental conditions.

Levels of Organization in Animals

• Biological Hierarchies: The organization within an animal's body ranges from simple structures like cells to complex systems such as organ systems, each playing a vital role in maintaining life.

• Homeostatic Regulation: Examining mechanisms of body temperature regulation serves as an excellent example of how internal control methods maintain stability amidst external fluctuations, emphasizing the relationship between anatomy and physiology in energy interplay within different environments.

Evolution of Animal Size and Shape

• Physical Constraints: Animals face limitations in size and shape due to physical laws governing strength, diffusion, and heat exchange. These constraints are pivotal in determining evolutionary outcomes in various species.

• Convergent Evolution: Similar adaptations often occur in unrelated species who face analogous environmental pressures, exemplified by swimming species that develop comparable body shapes for efficient movement.

• Body Size Challenges: As animals increase in size, they encounter significant challenges regarding energy consumption and locomotion efficiency, a principle illustrated by large dinosaurs such as Tyrannosaurus rex, which had a maximum speed significantly constrained by its massive body size compared to smaller species.

Exchange with the Environment

• Cellular Mechanisms: Nutrient and gas exchanges occur at the cellular level through diffusion across membranes, a fundamental aspect of metabolic processes.

• Multi-cellular Efficiency: For multi-cellular organisms, the need for efficient exchange systems is paramount. Specialized body plans, such as those seen in larger animals, facilitate this efficiency through adaptations like circulatory systems.

• Simple Organisms: Organisms with simpler designs, like Hydra, enable almost every cell to interact directly with their environment, underscoring basic biological principles of exchange.

Maintaining Homeostasis

• Concept of Homeostasis: Homeostasis refers to the maintenance of stable internal conditions despite fluctuations in external environments, a critical process for survival.

• Physiological Examples: Examples of homeostasis include the regulation of body temperature and solute concentrations, which are vital for the optimal functioning of biological systems.

Feedback Control Mechanisms in Homeostasis

• Negative Feedback: This mechanism serves to counteract changes from a set point, maintaining homeostasis. For example, in thermoregulation, if body temperature rises above a set point, the hypothalamus triggers sweating and increased blood flow to the skin, promoting heat loss. Conversely, if the body gets too cold, shivering and vasoconstriction occur to conserve heat.

• Positive Feedback: Unlike negative feedback, positive feedback amplifies physiological changes, pushing the system further away from its starting point. One prominent example is childbirth, where the release of the hormone oxytocin increases uterine contractions. As contractions intensify, more oxytocin is secreted, leading to even stronger contractions until delivery occurs. Another vital process is blood clotting; when a vessel is injured, platelets adhere to the site and release chemicals that attract more platelets, rapidly forming a clot to seal the wound.

Mechanisms of Homeostasis

• Set Point: Particular value that maintains homeostasis

• Stimulus: Fluctuation in the variable above or below the set point

• Sensor: Structure that detects changes in the body or its environment

• Response: Physiological activity that helps return the variable to the set point.

  -Ex. In the home heating example, a drop in temperature below the set point acts as

  a stimulus, the thermostat serves as the sensor and control center, and the heater produces the response.

Alterations in Homeostasis

• Regulated Changes: Some regulated changes occur during a particular stage in life, such as the radical shift in hormone balance that occurs during puberty.

• Circadian Rhythm: A set of physiological changes that occur roughly every 24 hours.

• The body's biological clock controls circadian rhythms, which continue despite changes in activity, temperature, and light. These rhythms usually align with day and night. For example, melatonin is released at night, especially more during longer winter nights. External factors can reset this clock, but not quickly, which is why traveling across time zones can cause jet lag, as the internal clock falls out of sync with local time.

Hierarchical Organization of Body Plans

• Tissue Hierarchy: The complex structure of living organisms is organized into tissues, which are further organized into organs, culminating in comprehensive organ systems responsible for specific physiological functions (e.g., digestive or circulatory systems).

• Functions of Organs: Each organ serves unique and specific roles; for example, the pancreas is vital in both the digestive system, where it aids in the breakdown of food, and the endocrine system, where it regulates blood sugar levels through hormone secretion.

• Types of Tissues: There are four primary types of tissues in animals: epithelial, connective, muscle, and nervous tissues—each class exhibiting specialized functions that contribute to the overall operation of the organism.

  • Epithelial Tissue: These tissues cover body surfaces and are involved in protective barriers, absorption, and secretion processes.

  • Connective Tissue: This category includes various tissues that bind organs together, store energy, and provide structural support (e.g., bones and cartilage).

  • Muscle Tissue: Responsible for movement, muscle tissue comprises three types: skeletal (voluntary movement), cardiac (involuntary movement of the heart), and smooth (involuntary movements in organ systems).

  • Nervous Tissue: Essential for signal transduction and coordination, composed of neurons that transmit impulses and glial cells that support neuronal function.

Coordination and Control Systems

• Major Control Systems: Animals possess two major control systems: the endocrine system, which employs hormonal signals for slower, more widespread responses, and the nervous system, which uses rapid neural signals for immediate reactions.

• Endocrine System: Signaling molecules released into the bloodstream by endocrine cells are carried to all locations in the body.

• Nervous System: Neurons transmit signals along dedicated routes connecting specific locations in the body.

• Hormones: Signaling molecules that are broadcast throughout the body by the endocrine system

• Nerve Impulses: Signals that travel to specific target cells along communication lines consisting mainly of axons.

Regulating and Conforming

• Regulator: An animal that uses internal mechanisms to control internal change in the face of external fluctuation.

• Conformer: An animal that allows its internal condition to change in accordance with external changes in the particular variable

• An animal may regulate some internal conditions while allowing others to conform to the environment.

Thermoregulation and Body Temperature

• Thermoregulation: Process by which animals maintain their body temperature within a normal range.

• Endothermic (warm-blooded): Using metabolic heat for temperature regulation ex. humans

  and other mammals, as well as birds.

• Ectothermic (cold- blooded): Animals that gain most of their heat from external sources ex. amphibians, many nonavian reptiles and fishes, and most invertebrates

• Ectotherms generally need to consume much less food than endotherms of equivalent size—an advantage if food supplies are limited.

• Temperature Variability: Poikilotherms experience body temperature fluctuations with external conditions, while homeotherms maintain a relatively constant body temperature.

• Ex. The largemouth bass is a poikilotherm, and the river otter is a homeotherm

• Heat Exchange Mechanisms: Various processes, including radiation, evaporation, convection, and conduction, contribute to thermal regulation. Adaptations for managing heat may involve insulation, blood flow regulation through vasodilation and vasoconstriction, and countercurrent heat exchangers that preserve core body temperature.

• Radiation: the emission of electromagnetic waves by all objects warmer than absolute zero. Here, a lizard absorbs heat radiating from the distant sun and radiates a smaller amount of energy to the surrounding air.

• Evaporation: the removal of heat from the surface of a liquid that is losing some of its molecules as gas. Evaporation of water from a lizard‘s moist surfaces that are exposed to the environment has a strong cooling effect.

• Convection: the transfer of heat by the movement of air or liquid past a surface, as when a breeze contributes to heat loss from a lizard‘s dry skin or when blood moves heat from the body core to the extremities.

• Conduction: the direct transfer of thermal motion (heat) between molecules of objects in contact with each other, as when a lizard sits on a hot rock.

• Integumentary System: Outer covering of the body, consisting of the skin, hair, and nails

Insulation

• Insulation: Reduces heat flow between an animal's body and its environment.

  • Found at body surface: hair and feathers;

  • Found beneath surface: layers of fat (adipose tissue).

• Oily Substances: Some animals secrete oils to repel water, protecting insulating properties of feathers/fur (e.g., birds apply oils while preening).

• Adjustable Insulating Layers:

• Land mammals and birds can raise fur or feathers in cold to trap additional air and increase insulation effectiveness.

• Humans rely primarily on fat for insulation; experience "goose bumps" as a vestige of hair raising.

• Marine Mammals:

• Heat transfer in water occurs 50-100 times faster than in air.

• Blubber: Thick layer of insulating fat under the skin, allowing maintenance of body core temperatures (36–38°C / 97–100°F) with less energy intake compared to land mammals of similar size.

Circulatory Adaptations

• Role: Circulatory systems regulate heat flow between the body's interior and exterior.

• Blood Flow Adjustment: Animals can change blood flow to manage heat based on external temperatures.

  • Vasodilation: Increases blood flow to the skin, enhancing heat loss via radiation and convection.

  • Vasoconstriction: Reduces blood flow to conserve body heat.

• Ectotherms: Marine iguanas control heat by vasoconstriction in cold water to keep core warm.

• Countercurrent Exchange: Allowed by adjacent arteries and veins, this process keeps warm blood from losing heat to the environment.

  • Seen in birds, mammals, sharks, and some insects to maintain muscle temperature for activity.

Behavioral Responses

• Behavioral Responses: Both ectotherms and some endotherms adjust body temperature through behavioral adaptations based on environmental changes.

  • When cold, they seek warmth by orienting toward heat sources and increasing exposure of body surface to heat.

  • When hot, they engage in behaviors such as bathing, moving to cooler areas, or adjusting their orientation to minimize sun exposure.

  • Example: Dragonfly’s "obelisk" posture reduces body surface area exposed to direct sunlight.

Adjusting Metabolic Heat Production

• Body Temperature Maintenance: Endotherms maintain body temperatures significantly higher than their environment, counteracting continual heat loss.

• Thermogenesis:

  • Ability to vary heat production to match heat loss.

  • Increased by muscle activity, such as moving or shivering.

  • Example: Chickadees (20 g) maintain a body temperature of 40°C (104°F) even in -40°C (-40°F) environments due to shivering.

• Nonshivering Thermogenesis:

  • Endocrine signals in some mammals cause mitochondria to produce heat instead of ATP when cold.

  • Brown fat tissue: specialized for rapid heat production, containing extra mitochondria; found in mammals, especially infants (5% of body weight in human infants).

  • Recent findings show brown fat in adult humans can increase with exposure to cool environments.

Acclimatization in Thermoregulation

• Birds and Mammals: Often adjust insulation for seasonal temperature changes:

  • Grow thicker fur in winter.

  • Shed fur in summer.

  • Helps maintain constant body temperature year-round.

• Ectotherms: Adjustments primarily at the cellular level:

  • Produce enzyme variants with different optimal temperatures.

  • Change proportions of saturated and unsaturated lipids in membranes (unsaturated lipids maintain fluidity at lower temperatures).

• Ectotherm Adaptations:

  • Some can survive subzero temperatures by producing "antifreeze" proteins.

  • These proteins prevent ice formation in cells, allowing survival in extremely cold waters, as seen in certain Arctic and Antarctic fish that can live in temperatures as low as -2°C (28°F).

Physiological Thermostats and Fever

• Location: Sensors for thermoregulation are concentrated in the hypothalamus, which also controls the circadian clock.

• Function: A group of nerve cells in the hypothalamus functions as a thermostat, activating heat loss or gain mechanisms depending on body temperature.

Mechanisms Activated:

• Low Body Temperature:

  • Inhibits heat loss mechanisms.

  • Activates heat-saving processes (e.g., skin vessel constriction).

  • Stimulates heat-generating actions (e.g., shivering).

• High Body Temperature:

  • Shuts down heat retention mechanisms.

  • Promotes cooling (e.g., skin vessel dilation, sweating, or panting).

Fever Development

• Fever: Elevated body temperature during bacterial and viral infections.

• Hypothalamic Adjustment: Fever reflects an increase in the hypothalamic thermostat's normal range; artificially raising hypothalamic temperature can reduce fever.

• Behavioral Fever in Ectotherms: Ectotherms like the desert iguana maintain elevated body temperatures (2-4°C/4-7°F) by seeking warmth during infections, demonstrating that fever can occur in both endotherms and ectotherms.

Energy Allocation and Use

• All organisms, including animals, use chemical energy for:

  • Growth

  • Repair

  • Activity

  • Reproduction

• Bioenergetics: overall flow and transformation of energy in an animal, impacting nutritional needs related to:

  • Size

  • Activity

  • Environment

Energy Allocation and Use

• Organisms classified by how they obtain chemical energy:

  • Autotrophs: Harness light energy to build organic molecules (e.g., plants)

  • Heterotrophs: Obtain chemical energy from food (e.g., animals)

• Animals digest food through enzymatic hydrolysis and absorb nutrients through body cells.

• ATP from cellular respiration and fermentation fuels cellular work for:

  • Metabolism

  • Functions of cells, organs, and organ systems

• Energy uses include:

  • Biosynthesis for body growth and repair

  • Synthesis of storage materials (e.g., fat)

  • Gamete production

• ATP production generates heat, released to the surroundings.

Energy Requirements and Metabolic Rate

• Energy Relationships: An animal's energy use is closely linked to its size, activity level, and biological processes, impacting its overall metabolic function.

• Metabolic Rate Defined: The metabolic rate, which measures total energy expenditure over a specified time frame, is influenced by several factors, including an animal's size, environmental temperature, age, and activity level.

• Types of Metabolic Rates: Basal Metabolic Rate (BMR) refers to the minimum metabolic activity level while at rest, and Standard Metabolic Rate (SMR) pertains to the metabolic rate of a fasting, non-stressed ectotherm at rest at a particular temperature.

Size and Metabolic Rate

• Larger animals have more body mass and require more chemical energy.

• The metabolic rate is consistently related to body mass across various sizes, approximately proportional to body mass to the three-quarter power (m^{3/4}).

• This relationship applies to both ectotherms and endotherms.

Energy Consumption Implications

• Energy expenditure per gram of body mass is inversely related to body size.

• Example: A gram of mouse tissue requires about 20 times more calories than a gram of elephant tissue.

• Smaller animals have a higher metabolic rate per gram, necessitating:

  • Higher breathing rate

  • Greater blood volume (relative to size)

  • Increased heart rate

Trade-offs in Body Size

• As body size decreases, the energy cost per gram increases.

• As body size increases, the energy cost per gram decreases, but a larger fraction of body tissue is needed for:

  • Exchange

  • Support

  • Locomotion

Torpor and Energy Conservation

• Animals can face extreme temperatures and food scarcity that challenge homeostasis.

• Torpor: A physiological state of decreased activity and metabolism to conserve energy during difficult conditions.

  • Many birds and small mammals exhibit daily torpor suited to their feeding patterns (e.g., bats feed at night and go into torpor during the day).

  • Chickadees and hummingbirds often enter torpor at night to save energy.

  • Endotherms in torpor are usually small and have high metabolic rates during activity.

• Temperature Changes in Torpor:

  • Chickadees: body temperature can drop by 10°C (18°F).

  • Hummingbirds: core body temperature can fall by 25°C (45°F) or more.

Hibernation

• Definition: Long-term torpor as an adaptation for winter cold and food scarcity.

  • Body temperature declines as the body’s thermostat lowers.

  • Some mammals cool to about 1-2°C (34-36°F); Arctic ground squirrels can enter a supercooled state below 0°C (32°F).

  • Periodic arousals every two weeks raise body temperature briefly.

  • Metabolic rates during hibernation can drop to 1/20th normal rates, allowing survival on limited energy stores.

Estivation

• Definition: Summer torpor that allows animals to survive high temperatures and scarce water conditions.

Circadian Rhythms in Hibernators

• Traditional belief held that hibernators exhibit daily biological rhythms; recent research indicates possible cessation of clock operations during hibernation.

  • Study on European hamsters showed molecular components of the biological clock cease oscillation during hibernation.

Acclimatization and Adaptation

• Key Distinctions: Adaptation denotes long-term evolutionary changes that enable species to better cope with environmental pressures, whereas acclimatization refers to short-term physiological adjustments in response to immediate stressors such as temperature or altitude variations.

• Ex. When an elk moves to higher altitudes, the lower oxygen in the air makes it breathe faster and deeper. This leads to losing more CO2, which raises the blood pH. After a few days, the elk's kidneys adjust and excrete more alkaline urine, bringing the blood pH back to normal.