unit 4: water balance, thermoregulation, and energetics

reptile water %

65-75%

amphibian water %

75-85%

water gains

drinking orally (reptiles) + food (preformed) + metabolic water + integument

water losses

integumentary (evaporation) + urine + feces + salt glands + respiration

salt water osmotic condition

ion concentration internal < external

hyposmotic

water moves out

fresh water osmotic condition

ion concentration internal > external

hyperosmotic

water moves inward

land osmotic condition

ion concentration internal > external
water moves out

ammonia

ammonotelic, highly soluble + toxic, aquatic species, best when water conservation is not a problem

urea

ureotelic, less toxic, more soluble + energy, many terrestrial vertebrates (adult amphibians)

uric acid

uriotelic, reptiles, insoluble white precipitate (semi-solid urine), little water loss, most energy

water gain via physical transport

lacks rain harvesting posture and relies on capillary action

water absorbing posture

maximizing contact of ventral (stomach) surface with damp substrate

frog seat patch

ventral pelvic patch that functions to absorb water from substrate

preformed water

comes from food! large source

Hyla chrysoscelis water loss posture

minimizes surface area exposed, reduces evaporative water loss through the skin => CROUCHED!

waxy leaf frog

wiping behavior, spreads lipids from gland in the skin near rear end

African bullfrog cocoon

formed by shed skin cells and mucus, reduce the rate of cutaneous water loss

salt glands

help with the removal of salt, located in the head/mouth of herps

Kinosternon baurii salt tolerance

leaves freshwater habitat that has been flooded by sea water after it reaches 50% salinity

sea snakes

some spend time on land, others entirely marine

set-point temperature

the thermostat setting that signals when an animal should initiate body temperature regulation

raise temperature

go from light color to dark color

lower temperature

go from dark color to light color

heliothermic

rely on solar radiation for thermoregulation, Texas horned lizard

kleptothermy

heat energy stolen from endotherms, sea kraits and shearwaters

Galapagos marine iguana

faces Sun directly, capillaries in head dilate to shunt warm blood to body, upward posture allows cool air to flow beneath to cool

capsazepine

inhibits thermoregulation behavior in reptiles

low energy demand

herps can use particular adaptive zones because those zones are characterized by limited resource supply

resting metabolic rate of herps

10-20% that of birds and mammals of similar size

small body sizes

due to their low metabolic rates and ectothermy, have access to a world that larger species cannot access

elongate tetrapods

existence depends upon ectothermy (snakes, legless lizards, caecilians, most salamanders)

weasels

lose twice as much energy at low ambient temperatures as do wood rats of similar body mass

brumation

behavioral response in ectotherms to changing seasons and resource availability, extended change in metabolic requirements

brumation environments

removes animal from temperatures low enough to kill, underground, underwater, rock outcrop, inside hollow tree, cavity temp > ambient

freeze tolerance

the ability to chill your body below freezing (0 C) and survive, allows for early breeding

freeze tolerance limitations

freezing is lethal because the formation of ice crystals physically damages cells and tissues

freeze tolerance animals

4 species of frogs, several turtles, lizard and snakes

wood frog (Lithobates sylvaticus)

model system for freeze tolerance understanding, cells dehydrate, liver produces glucose-based antifreeze

aestivation

inactivity during prolonged periods of heat and drought, death by dehydration occurs quickly, cocooning

western spadefoot toad (Spea hammondi)

spend > 90% of their lives inactive

body temp during periods of inactivity

drops close to ambient levels with a consequent reduction in metabolic rate

ingested energy

devote a large amount to producing new biomass, doesn’t go to metabolism