Temperature and Water

Water: Gain = Loss Gain – liquid water – preformed water – metbolic water. Loss – Evaporation – Urine – Feces – Salt glands

Routes of water gain: Liquid Water Pools and puddles, water drops, film of water. Harvesting fog and condensation, rain harvesting in Crotalus scutulatus (Mohave rattlesnake)

Moloch and Phrynosoma: water transport on skin: note postural differences. Reliance on adhesion and cohesion.

Scale hinge joints form channels for water movement. Movement of jaws draws water along channels.

Note flanged lip on marginal scutes of carapace. Desert tortoise also builds basing at the bottom of slopes to harvest rainwater during seasonal rains (increase body mass by > 9%.

Osmotic water gain (and loss) Anurans can absorb water through the skin (pelvic patch). They do not drink. Use AVT (arginine vasotocin), similar to ADH, to stimulate uptake of water, reduce urine production, and increase reabsorption from bladder. Spadefoot toads (Scaphiopus hammondi) – 9 mo / yr in burrow. At start, bladder is 100 mosm and blood is 300 mosm

Spadefoots Spadefoot toads (Scaphiopus hammondi) – 9 mo / yr in burrow. At start, bladder is 100 mosm and blood is 300 mosm – At first, protein metabolism does not increase bladder conc., even though urea is clearly being produced. – Therefore, some water is absorbed form soil while in the cocoon. – By June, before rains, plasma conc is as high as 600 mosm while bladder is 300. They use the high osmolality to continue to absorb water from the soil. The bladder provides source of water to limit plasma osmolality.

Mason Williams

Amphibians in fresh water Plasma is 250 mosm, water is 2 mosm. – Therefore, influx of water. – Produce large volume of dilute urine. – Lose salts to the water, so must actively uptake salts from water. Amphibians in brackish or marine environments – Increase plasma concentration of sodium and urea

Preformed water Chuckwallas Plants in diet (Creosote) contains 72% water in early May. By late May, water content is down to 51%. When water content drops to 63% they stop eating because they lose more water in the urine and feces than they gain from their food.

Heloderma suspectum Prey contain some water, but cost of excretion and fecal loss exceeds intake. Plasma osmolality increases in summer months.

Metabolic Water H from food and oxygen from atmosphere combined to form water. 1 g of starch yields.556 g of water. 1 g of fat yields g of water. Metabolism of protein to urea produces g of water. Metabolism of protein to uric acid produces g of water.

Water Loss Evaporation from skin: recall the stratum corneum from previous lecture. Amphibians – Terrestrial and aquatic: low cutaneous resistance of s/cm – Arboreal rhacophorids and hylids: 10 – 120 s/cm. – Waterproof frogs Chiromantis and Phyllomedusa: 200 – 900 s/cm.

Phyllomedusa

Cocooning: cocoon has 50 x resistance to water loss than skin

Respiratory water loss Rate of loss increases with temperature and metabolic rate. Rely on counter-current idea. Use microhabitats with higher humidity.

Urine and Feces Protein metabolism – Ammonotelic – excrete ammonia: cheap metabolically, requires water, and toxic, so must be voided quickly. – Ureotelic – excrete urea: more expensive, 4 moles of ATP for each mole of urea, only slightly toxic. – Uricotelic – excrete uric acid: expensive, 24 moles of ATP / mole of uric acid. Aquatic anuran bladders hold 5% of mass, Terrestrial anuran bladders hold as much as 60%

Salt Glands

Water Ecology of Herps: Behavioral control by Eleutherodactylus coqui – competing demands of reproduction and water balance.

Urine as a water reserve for Gopherus agassizii

Louis Agassiz: Founded Museum of Comparative Zoology at Harvard, anti Darwinian.

Urine as a water reserve for Gopherus agassizii

Sea snakes: totally aquatic forms drink from freshwater lens after rain.

Kleptothermy

Response to infection

Endothermy in Pythons

Evolutionary Ecology of set points