1. Water Balance in Terrestrial Animals

2. Recurring themes in physiological ecology
Economy: balancing gains and losses
water, heat, and energy
Effects of body size and shape
importance of surface area-to-volume ratio
Effects of climate
adaptations to extreme conditions
Differences among terrestrial animal taxa
mammals, birds, reptiles, amphibians, arthropods

3. Variation in Water Availability
Concept 4.3: The water balance of organisms is determined by exchanges of water and solutes with the external environment.
Water is the medium in which all biochemical reactions necessary for life occur.
Water has unique properties that make it a universal solvent for biologically important solutes.

4. Water Availability
The tendency of water to move down concentration gradients, and the magnitude of those gradients, determine whether an organism tends to lose or gain water from its environment.
Must consider an organism’s microclimate in order to understand its water relations.

5. Variation in Water Availability
Maintaining optimal water content is a challenge for freshwater and terrestrial organisms.
Ocean waters maintain the water balance of marine organisms.
Terrestrial species lose water to a dry atmosphere.
Freshwater organisms lose solutes to and gain water from their environment.

6. Adaptations to environmental conditions can be anatomical, morphological, physiological, or behavioral
Anatomy = internal structure of an organism, including size, shape, and position of it organs
Morphology = external structure of an organism, including its overall size and shape
Physiology = study of the functions of living cells, tissues, and organs

7. Effect of body size on rate of evaporative water loss
Surface area-to-volume ratio increases as body size decreases
Evaporative water loss increases as surface area-to-volume ratio increases

8. Example: compare 1 cm x 1 cm x 1 cm cube with 10 cm x 10 cm x 10 cm cube
Large
animal 10 1
Small animal 1 1 10
Surface area = 1x1x6 = 6 cm2
Volume = 1x1x1 = 1 cm3
SA:V ratio = 6:1 = 6.0
Surface area = 10x10x6 = 600 cm2
Volume = 10x10x10 = 1000 cm3
SA:V ratio = 600:1000 = 0.6

9. Sources of Water Gain
1. Free liquid water = found in lakes, rivers, puddles, dewdrops, etc.
2. Preformed water = obtained through food with a high moisture content
3. Metabolic water = produced through breakdown of nutrients in an animal’s diet
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O

10. Water Gain Some insects can extract water vapor from the air.
mechanism not fully understood
e.g. grasshoppers, lice

11. Water Regulation on Land - Animals
Wia= Wd + Wf + Wa - We - Ws
Wia= Animal’s internal water
Wd = Drinking
Wf = Food
Wa = Absorbed by air
We = Evaporation
Ws = Secretion / Excretion

12. Water Regulation on Land - Animals

13. Water Balance Inputs Outputs Cutaneous Drinking
Uptake through roots
Uptake through body wall (amphibians)
Water in food
Metabolic water
Where does this come from?
Outputs
Cutaneous
leaking through outer surface (skin, exoskeleton)
Respiratory
panting, breathing, transpiration
Excretory
Feces
Urine
Other secretions: sweat, tears, milk

14. Reducing Water Loss Cutaneous water loss:
Stay in cool/moist microclimate; venture out when relative humidity is high.
Use relatively impermeable materials on outer surface, such as scales, waxes, etc.
Don't sweat
Decrease surface area (e.g., small leaves)
Reduce surface temperatures of body by shading (hairs/spines, etc.)

15. Reducing Water Loss Respiratory Water Loss
Stay in moist microclimate (e.g., burrow); venture out when relative humidity is high.
Kangaroo rats plug the burrow entrance in daytime to reabsorb moisture from their breath.
Nasal water condensation: evaporative cooling in the nasal passageways cools exhaled air.
Minimize the length of time stomates are open
See photosynthesis notes (later)

16. Reducing Water Loss Excretory Water Loss:
Concentrate urine (e.g., The Kangaroo Rat is capable of producing urine twice as concentrated as seawater).
Dry feces (e.g., Kangaroo Rat droppings are five times drier than lab rat feces).
Produce uric acid rather than urea -- uric acid requires 10x less water than urea to rid the same amount of waste.

17. Reducing Water Loss
Efficient kidneys that shunt water from waste products, resulting in water conservation.
Highly concentrated urine or pellets of uric acid
Large intestine reabsorbs most water and produces very dry feces.

18. Amount of water lost through excretion depends on type of excretory product
Birds and most reptiles excrete uric acid which doesn’t require much water to eliminate
Mammals and most amphibians excrete urea, which requires more water to eliminate
Tradeoff: more energy required to produce uric acid than to produce urea

19. Water balance example: Kangaroo Rat
Water gains:
Free water 0.0 ml
Preformed water 6.0 ml
Metabolic water 54.0 ml
Total ml
Water losses:
Urine ml
Feces ml
Evaporation ml
Total ml

20. Adaptations for Desert Life
Behavioral Adaptations

21. Drink more water

22. Burrowing
Organisms are exposed to little or no sunlight. Therefore cooling strategies that use water such as sweating, panting, etc. need not be employed, and water is thus conserved.
Some species of rodents purposely pant inside the burrows in order to make the water available for a second round of consumption.
Use of shady micro-habitats is similar in function to burrows in that they enable an organism to reduce overall exposure to high light and temperature levels.

23. Gular/tongue fluttering; a cooling method.

24. Burrowing Owls
Desert Tortoise

25. Shade Microhabitats
Desert Horned Lizard
Cactus Rat

26. Timing of Activity
Nocturnal or crepuscular (dawn/dusk) activity reduces the amount of exposure to light and heat extremes.
Scorpions
Aardvark

27. Body “Acrobatics"
Body positions are altered in order to reduce surface contacting the hot surface or to increase surface area where moisture may be collected from morning fogs common to many desert mornings.

28. Shovel-snouted Lizard (Meroles anchietae)

29. This beetle (Stenocara sp) is collecting moisture falling from a thorny branch in the Namib Desert. They also collect water from coastal fog. See article link on web page.

30. Adaptations to desert life
Behavioral:
Including food items with high preformed water content in diet, when possible
Aestivation = seasonal dormancy during hottest and driest time of year

32. Aestivation

33. Adaptations for Desert Life
Morphological Adaptations

34. Morphological Adaptations
Some desert animals have body parts specially adapted for fat storage (e.G. Camel’s hump, Gila Monster’s tail)
Fats when digested yield greatest amount of metabolic water of any nutrient

35. Morphological Adaptations
Water can be stored in the roots, stems, and/or leaves of plants (plants that do this are called succulents).

36. Morphological Adaptations
Long nasal passages
Nasal water condensation: evaporative cooling in the nasal passageways cools exhaled air.
Warm body temp and hi moisture level in lungs
Air cools in nostrils as it leaves and water is reabsorbed
Because cooler air holds less water than warmer air, water in the cooled, exhaled air condenses along the nasal passages.
The longer, narrower, nasal passages found in many desert animals cools air further and condenses more water.

37. Sable Antelope

38. Adaptations for Desert Life
Physiological Adaptations

39. Adaptations to desert life
Physiological
Kidneys produce highly concentrated urine (long loops of Henle)
Large intestine reabsorbs most water and produces very dry feces
Exhaled air is cooled in the nasal cavity before leaving the body
Some animals can use metabolic water to meet all of their water needs

40. Tolerate Dehydration
Many of the desert plants (e.g., this prickly pear cactus) and animals (e.g., desert toads) can tolerate great losses of water out of their bodies without dying.

41. Tolerate Dehydration
Toleration of temperature changes where the organism's internal temperature rises and falls along with outside temperatures is another adaptation to extreme environmental changes. This conserves water that would be lost with sweating or panting.

43. Gloger’s rule
Animals of a given species tend to be darker in color in humid environments and lighter in arid environments
Pacific Northwest merlin
(wet climate)
Prairie merlin
(dry climate)

44. Marine air-breathing vertebrates
Includes groups of mammals, birds, and reptiles, but no amphibians
Marine environment presents challenges similar to desert because drinking salt water causes dehydration unless excess salt is eliminated

45. Adaptations to marine environment
Salt glands of reptiles and birds secrete concentrated sodium chloride solution
Marine mammals produce concentrated urine and avoid drinking sea water
Milk of lactating marine mammals is very concentrated
Albatross excretes excess salt
through tubes on its bill

47. Water Balance in Aquatic Organisms
Body concentration can be similar to ambient env.
Many marine invertebrates use osmosis to equilibrate solute concentrations by moving water. (review isotonic, hypotonic, hypertonic)
very efficient - no energy expenditure

48. Water Balance in Aquatic Organisms
Sharks are hyper-osmotic to seawater
so water diffuses in
by decreasing osmotic gradient b/t body and env, they cut the cost of osmoregulation
Bony fish are hypo-osmotic to seawater
lose water constantly
must drink seawater and eliminate extra salt

50. Water Balance in Aquatic Organisms
Marine Fish and Invertebrates
Isomotic organisms do not have to expend energy overcoming osmotic gradient.
Sharks, skates, rays - Elevate blood solute concentrations hyperosmotic to seawater.
Slowly gain water osmotically.
Marine bony fish are strongly hypoosmotic, thus need to drink seawater for salt influx.

52. Water Balance in Aquatic Organisms
Freshwater Fish and Invertebrates
Freshwater organisms must minimize water gain
impermeable body surfaces - cheap
efficient excretory systems - energetically costly
e.g. contractile vacuoles of protozoa
Hyperosmotic organisms that excrete excess internal water via large amounts of dilute urine.
Replace salts by absorbing sodium and chloride at base of gill filaments and by ingesting food.

54. Contractile vacuole
full
empty

56. Genetically Based Differences
Identification of Mechanisms of Natural Selection (population-level studies)
Breeding Experiments: Are the traits heritable?
Selection Experiments: Determine which combination of features results in higher fitness in a specific, experimental environments.

57. Adaptations to desert life
Anatomical
Some desert animals have body parts specially adapted for fat storage (e.g. camel’s hump, Gila monster’s tail)
Fats when digested yield greatest amount of metabolic water of any nutrient

58. Dissimilar Organisms with Similar Approaches to Desert Life
Camels
Can withstand water loss up to 20%.
Face into sun to reduce exposure.
Thick hair: Increased body temperature lowers heat gradient.
Saguaro Cactus
Trunk / arms act as water storage organs.
Dense network of shallow roots.
Reduces evaporative loss.

62. Two Arthropods with Opposite Approaches to Desert Life
Scorpions
Slow down, conserve, and stay out of sun.
Long-lived
Low metabolic rates
Cicadas (Diceroprocta apache)
Active on hottest days.
Perch on branch tips (cooler microclimates).
Reduce abdomen temp by feeding on xylem fluid of pinyon pine trees.