Mammals

Mammals

1. Water Gain

   • Drinking
     • Unreliable source
       • Rainfall unpredictable
         • Arid = 6 - 10mm, Semi-arid = 50mm +
         • Flashfloods
     • Specialist actions to reduce dehydration
       • Camel
   • Environment
     • absorption of moisture in dens or burrows = condensation on cool walls
   • Diet
     • Omnivores can obtain 70% of water from insects

2. Water Loss

   • REWL (Respiratory evaporative water loss)
     • Nasal Counter-current exchange
       • Affected by the surface area
     • 100% saturated air
       • Delicate structures of the lungs must be damp
       • Camels do not breath out 100% saturated air
   • TEWL (Transepidermal evaporative water loss)
     • Mammalian skin permeable and allows water to pass through

3. Stratergies for reducing water loss

   • Concentratation of Nitrogenous waste
     • Faeces
       • Can dehydrate faeces - depending on species
     • Urine
       • Effective kidney function
         • Loop of Henle (Counter current multiplyer system)
         • Can respond to dehydration by concentrating urine
       • Hyperosmotic to plasma
       • Ureotylic - production of urea = less water intensive than uric acid, but slightly more toxic

4. Large Mammals = Endurer

   • Camel
     • Can rehydrate 200 liters in 3 minutes
       • Stores water in the gut to avoid blood dilution
     • Enhanced nasal counter-current exchange
     • Heterothermic - when depreived of water can slowly increase body tempr from 35 - 41 C during the day and lose heat during the night
     • Does not require EWL to reduce body temperature (saves 5 liters of water a day)
     • Can store urea in tissue when dehydrated
   • Sand Gazelle
     • Heart and liver shrinks during times of starvation or dehydration
       • Smaller hearts = lower metabolism = reduction in water by 1/3
       • Ostrowski et al, 2006
   • Lower metabolism = lose heat slower = lowered EWL
   • Kangaroo
     • High urine concentration - 3700mOsmol
     • Lowered rates of metabolism and a lowered body temperature
       • Reduction in REWL
     • Circadian locomotory rhythm = many are nocturnal
     • Lie in cool soil to reduce body temperature in hot days
       • Vasodilation = lick forarms to cool blood down
     • Red Kangaroo VS Grey Eastern Kangaroo

5. Small Mammals = Evader

   • Kangaroo Rat
     • Eat a carb rich diet and still stayes hydrated by obtaining water from seeds
       • Knut Schmidt-Nielson (1951)
         • Fur lined cheek pouches
     • Dry faeces reduces nitrogenous water loss
     • 90% of water gained by metabolism, 10% absorbed by dry food
     • 25% of water lost by urine, 5% lost by faeces, 70% lost by EWL
   • Higher metabolism = lose heat quicker = higher EWL