Theme 4 Flashcards
Terrestrial Animals Key Points
Relatively few terrestrial lineages
Requirements for a terrestrial life include:
- Desiccation avoidance
- Desiccation tolerance (aestivation, life cycles)
- Excretion with limited water loss
- Internal bulk flow of fluids and gasses
- Gas exchange with air
Desiccation And The Environment – Terrestrial Animals
- Constant water loss through evaporation: across the wet respiratory membrane, across the surface of the skin
- Water loss in urine and feces
- Some species lose water through thermoregulatory methods (sweating, panting)
Desiccation (terrestrial animals) requirements:
- Waterproofing of outer layer of the body: (keratin, wax)
- Minimal exposure of gas-exchange and digestive surfaces to air (internal placement)
Loop of Henle aids in the conservation of
water in mammals, produces concentrated urine – hyperosmotic to blood
Kangaroo Rats Desiccation:
- Very long Loop of Henle
- Produces a small quantity of highly hyperosmotic urine (22.5% of daily water loss – for a human, water loss in urine is 57.7%)
Desiccation And The Environment – Insects
- Must deal with small size (cube-square relationship favours evaporative water loss from body surface) and inevitable evaporative loss from wet respiratory surfaces in tracheae
- Waxy outer layer of the cuticle minimizes evaporative water loss from the body surface
- Spiracles permit closing of the tracheal system, cuts down on evaporative water loss
Desiccation Tolerance
Terrestrial tardigrades live in water films in damp environments
- Cryptobiosis: formation of the resistant stage (tun) in response to environmental challenges (dehydration, sub-zero temperatures)
- Anhydrobiosis: when slowly desiccated, resistant tun formed – when re-hydrated, tardigrade returns to active state
Nitrogenous Wastes
- Toxic ammonia (NH3) is produced in every cell of the body by catabolism of amino acids and nucleic acids
- Mammals convert NH3 to less-reactive urea and flush it away in urine = inevitable water loss in excretion of nitrogenous wastes in mammals (Loop of Henle reduces this)
- Reptiles, birds and insects convert it to uric acid – very low water-solubility, semi-solid nitrogenous wastes can be excreted while conserving water
Bulk Transport
- Larger and more complex animals - transport system necessary to carry fluids and solutes to within 0.01 mm of most cells in the body to support a reasonably active metabolism
- This requires a transport fluid (blood, hemolymph) and a circulatory system to deliver it to within this distance of every cell in the body
Disadvantages of Breathing Air
- CO2 does not diffuse into the air as easily as into water
- Inevitable evaporative water loss from internal respiratory surface, which must be kept wet
Advantages of Breathing Air
- 21% O2 – much greater than water
- Bulk flow of air (ventilation) requires less muscular effort (low viscosity, low density)
Gas Exchange With Air - Insect tracheal system
- Delivers air directly to tissues (via interstitial fluid)
- Moist exchange surfaces are internal
- Form of a bulk flow system for air
Gas Exchange With Air - Vertebrate Lungs
- Bulk flow of air to respiratory membrane
- Moist exchange surfaces internal
- Requires muscular effort (ventilation)
More requirements for terrestrial life:
- Protect gametes from desiccation
- Protect embryo from desiccation
- Temperature extremes
- Constraints on sensory systems
- Support body weight
Protect gametes from desiccation
fertilization without water (internal)
Protect embryo from desiccation
- Aquatic larvae, thick covering on egg/embryo
- Amniote vertebrates ( birds/reptiles/mammals) – amniotic membrane
Temperature extremes
- Avoid via thermoregulation
- Tolerate
Constraints on sensory systems
- Chemosensors
- Mechanosensors – tympanal organ, vert. middle ear
Support body weight
- Robust skeleton
- SA/V relationships, size, stance
Amphibians – Reproduction in Water
- Amphibians lay anamniotic eggs in the water but metamorphose into a form that can live on land to some degree
- Embryos can exchange gasses and wastes with the aquatic environment
Reasons For Thermoregulation
- Most terrestrial animals regulate their body temperature when possible through metabolic activity or behaviour
- Animal body temperature range ~4°C - 40°C
< 0°C - ice crystals damage cells
> 45°C – proteins denature
Ways Of Thermoregulation
- Endothermy
- Ectothermy
- Heterothermy
- Homeothermy
Endothermy
The production of sufficient metabolic heat to warm the tissues significantly
Ectothermy
Insufficient heat from metabolic activities to warm tissues significantly; heat must come from the environment
Heterothermy
Allowing body temperature to vary with the environment
Homeothermy
Tightly regulating body temperature around an unvarying mean
Distinguishing endotherms vs. ectotherms is based on metabolic rate
- endotherms: metabolic rate changes with temperature in order to maintain a constant body temperature – a cost
- ectotherms: metabolic rate changes directly with body temperature, which changes with environmental temperature
Reasons For Thermoregulation
- Performance depends upon biochemical processes
- Animals regulate temperatures within the range allowing optimal performance
Heat Exchange With The Environment Occurs Via:
Conduction, radiation, convection, and evaporation
Conduction
- Direct heat transfer by contact – air conducts heat poorly, water well
- Gill-breathing aquatic organisms tend to be isothermic with the water in which they swim
Radiation
- Transfer of heat as long-wave light – not very effective as a heat sink at biological temperatures
- Radiative sources (the sun) are very effective for heating up
Convection
- Transfer of heat by a moving medium – air or water flowing over an organism carries heat away or brings it
Evaporation
Energy consumed by the change from liquid to gas; effective way to carry heat away
Ectothermic animals can thermoregulate by using
Conduction, radiation, convection, and evaporation alone for heat exchange with the environment
Countercurrent Heat Exchange
- Cold-climate terrestrial endotherms can conserve heat by using counter-current heat exchange structures – regional heterothermy
Torpor
- Reduces energy demands in small endotherms during periods of low or high environmental temperatures, or resource unavailability
- Body temperature setpoint drops
- Metabolic rate slows
Hibernation
Seasonal version of torpor, undertaken during seasonal periods of low temperature
Endothermy In Insects
- Bees and some other flying insects are heterothermic endotherms
- Generate sufficient heat by the action of the flight muscles to maintain a high constant temperature in the thorax
- Tend to be furry
Freeze Tolerance and Freeze Avoidance
- Some ectotherms can supercool their ECF – goes below 0° C without freezing
- Some terrestrial ectotherms can allow the bulk of their ECF to freeze for extended periods (high intracellular osmolality depresses the freezing point, control of ice nucleation in ECF)
Chemosensors
- Chemosensory organs – require a wet surface for adsorption of air-borne chemical particles
- Insect antennae have minute channels lined with moist adsorptive tissue
- Terrestrial vertebrates have moist olfactory epithelium and taste buds in the buccal cavity
Hearing
- Sound does not transmit easily from air to water
- Sensing soundwaves by terrestrial animals must take this into account
- Insects – tympanal organs – air on both sides, nerves pick up vibrations
- Hearing in aquatic vertebrates – inner ear can pick up vibrations through tissues
- In fish, hyomandibular bone suspends the lower jaw
Hearing in Mammals
- middle-ear bones transform large-amplitude eardrum vibrations to low-amplitude high-force vibrations transmitted to oval window of inner ear, which amplifies vibrations so that waves are produced in fluid-filled inner ear
Support Body Weight
- Cross-sectional area of limb (support) is a function of size squared
- Volume (mass) is a function of size cubed
- All else being equal, as animals get bigger body MASS would increase faster than the cross-sectional AREA of the limbs for support
- Thus, in terrestrial animals, if body and limbs scale proportionately/linearly with size, at some point body mass exceeds the ability of the limbs to support it
- Limbs must change disproportionately to body size as terrestrial animals get larger – allometric growth
- Some ‘animals’ are impossibly big
- Water supports the body mass
Allometric growth
- Produces limbs that can support increasing body weight with increasing size
- Characteristic of most animals
- An evolutionary phenomenon associated with trends in increasing or decreasing size in a lineage
Hard Skeletons
- Two types: exoskeletons (external) and endoskeletons (internal)
Functions:
- Provide attachments and leverage for muscles = force transmission
- Transmit compressive stress to the substrate
- Provide a framework for tissues of body
- Act as a mineral bank for physiological requirements (vertebrates)
- Protection for delicate organs or whole body
Endoskeletons
- In vertebrates, composed of bone and cartilage
- Bone: collagenous matrix mineralized by CaPO4 crystals
- Highly vascularised, matrix architecture supports scattered osteocytes
- Metabolically active
- Bears compressive stress well, shear stress not so well
Exoskeletons
The arthropod exoskeleton:
- consists of chitin – long complex polysaccharide
- may be impregnated with calcium carbonate
Composed of plates (tergae) with joints between them
- muscles are within the skeleton
Hydrostatic Skeletons
- Volume of fluid enclosed by 2 layers of muscle, longitudinal and circular
- Fluid incompressible but pressurized when muscle contracts
- Muscular “container” changes shape with the contraction of different muscle layers (organ, animal’s whole body)
What’s good about being aquatic:
- Water supports the body (affects the size, stance and skeleton)
- Desiccation is a lesser threat
- Stable and mild temperatures
- Metabolic waste removed by water
- Sound transmits well from water to the body
Aquatic animals can become much bigger than terrestrial animals
The biggest aquatic animals are air-breathers
Challenges of living in aquatic environments:
- Water is dense
- Water is viscous
- Water has low oxygen content compared to air
- Water has a high thermal conductance
Being warm in aquatic environments
- Water is a good heat conductor = aquatic organisms are mostly heterothermic ectotherms
- Aquatic homeothermic endotherms must deal with rapid loss of body heat
- Insulation: fur, feathers, fat
- Respiratory medium: breathe air, allows higher metabolic rate; also, the air is a poor conductor of heat from the body
- Aquatic endotherms utilize counter-current heat exchange – allows outbound blood to heat inbound blood – retains heat by maintaining gradient along parallel lengths
