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Biology 2672a: Comparative Animal Physiology Water balance in terrestrial animals.

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Presentation on theme: "Biology 2672a: Comparative Animal Physiology Water balance in terrestrial animals."— Presentation transcript:

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 Respiratory Urine Faeces Sweat/ excretion/ evaporation across skin Drinking Water in food Metabolic water in food Absorption (not in mammals!) Metabolic

4 Metabolic water from food Table 26.3 Difference in the amount of water used to process the food along different pathways

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 Gibbs et al. 1997 J. Exp. Biol. 200:1821-1832 D flies survive for longer D flies carry more bulk water (mostly bound to glycogen)

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 don’t tolerate any more water loss than controls

10 Extreme: Survive losing more water by anhydrobiosis!  Some small aquatic animals can tolerate the loss of >99% of their body water Also see Box 26.4 Nematodes Artemia (cysts) Rotifers Tardigrades

11 Anhydrobiosis  Polypedilum vanderplanki

12 Losing water slowly works!

13 Lose water more slowly Respiratory Urine Faeces Sweat/ excretion/ evaporation across skin Metabolic

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 Fig 27.14 Hot air in lungs holds lots of air when saturated Air cooled in nasal passages, moisture condenses

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. 27.12 Fig. 27.20

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 Respiratory Urine Faeces Sweat/ excretion/ evaporation across skin Drinking Water in food Metabolic water in food Absorption (not in mammals!) Metabolic

22 Telling between the strategies % original water Time Water loss survived Survive losing more water Lose water more slowly Carry more water

23 Reading for Thursday  Way to Pee!: Kidneys and urine formation  Pp715-744


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