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