Biology 2672a: Comparative Animal Physiology

1
Biology 2672a Comparative Animal Physiology

• Water balance in terrestrial animals

2
Desiccation is the single biggest problem for
life in terrestrial habitats

• Only a few phyla have made it on land
• Essentially aquatic
• Nematoda
• Tardigrada
• Moderately successful
• Onychophora
• Mollusca
• Highly successful
• Arthropoda
• Vertebrata

3
Water in and out
Sweat/ excretion/ evaporation across skin
Absorption (not in mammals!)
Respiratory
Metabolic
Drinking
Water in food
Faeces
Metabolic water in food
Urine
4
Metabolic water from food
Difference in the amount of water used to process
the food along different pathways
Table 26.3
5
How to survive in desiccating (ie terrestrial)
environments?

• Carry more water
• Survive losing more water
• Lose water more slowly

6
Carry more water
7
Carry more water II
Selection of Drosophila for desiccation resistance
D flies survive for longer
D flies carry more bulk water (mostly bound to
glycogen)
Gibbs et al. 1997 J. Exp. Biol. 2001821-1832
8
Carry more water III

• Most terrestrial amphibians can store 20-50 of
  their body weight as urine in their bladder
• As they desiccate
• plasma becomes hyperosmotic to urine
• Bladder becomes permeable to water
• Active pumping of NaCl out of bladder
• Water is reabsorbed from bladder into plasma.

9
Survive losing more water

• Start with the same amount of water, but tolerate
  losing a larger proportion of that water
• Camels tolerate 30-40 loss of body weight by
  dehydration
• (most other mammals 10-15 )
• Desiccation-selected flies dont tolerate any
  more water loss than controls

10
Extreme Survive losing more water by
anhydrobiosis!

• Some small aquatic animals can tolerate the loss
  of gt99 of their body water

Rotifers
Nematodes
Artemia (cysts)
Tardigrades
Also see Box 26.4
11
Anhydrobiosis

• Polypedilum vanderplanki

12
Losing water slowly works!
13
Lose water more slowly
Sweat/ excretion/ evaporation across skin
Respiratory
Metabolic
Faeces
Urine
14
Evaporative water loss (EWL)

• Respiratory
• Cutaneous

15
EWL varies between species
Fig. 27.16
16
Minimising respiratory water loss I
Countercurrent heat exchange to retain moisture
Hot air in lungs holds lots of air when saturated
Air cooled in nasal passages, moisture condenses
Fig 27.14
17
Camels

• Have a countercurrent exchanger in their nose
• reduce evaporative water loss
• Allow their body temperature to rise during the
  day and fall at night
• reduce water loss from panting or sweating

18
Minimising respiratory water loss II Spiracles
in arthropods
Fig. 22.29
19
Minimising cuticular water loss

• Waxy cuticle
• All animals!

Fig. 27.20
Fig. 27.12
20
Reducing excretory water loss

• Efficient kidneys
• Get rid of a lot of salt and wastes per unit
  water
• Mammals, birds, insects
• See next lecture for mechanisms
• Efficient re-absorption of water from gut
• Dry Faeces

21
Water in and out
Sweat/ excretion/ evaporation across skin
Absorption (not in mammals!)
Respiratory
Metabolic
Drinking
Water in food
Faeces
Metabolic water in food
Urine
22
Telling between the strategies
Carry more water
original water
Lose water more slowly
Water loss survived
Survive losing more water
Time
23
Reading for Thursday

• Way to Pee! Kidneys and urine formation
• Pp715-744