chapter 6

water balance

gain is equal to loss

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water is a solvent

water gain: liquid water

only reptiles make use of liquid water

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mouth

water gain: water harvesting by reptiles (snakes specifically)

ex: snake (peringuey’s adder) lives in namib desert and obtains water/moisture through ocean breeze

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hydrophobic scales: water beads up on body

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1. ambush posture
2. rain collecting posture

water gain: ingestion of liquid water by amphibians

do not drink, rather absorb water through permeable skin

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1. pelvic patch
2. bladder holds water

preformed water

this is part of whatever food the animal eats

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animals usually have 70-80% water

metabolic water

water is a byproduct of metabolism

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1. carbs
2. fats
3. proteins

evaporation

requires a permeable barrier

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occurs through:


1. cloaca
2. skin
3. mouth

water loss prevention: mucus glands

amphibians/reptiles

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secretes a watery mucus over the skin (made of dead cells filled with keratin)

water loss prevention: wax glands

amphibians/reptiles (waxy leaf frog)

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lipid gland (specialized gland) creates a lipid layer over the skin

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even better barrier for water loss (than mucus glands)

water loss prevention: mesos layers

amphibians/reptiles

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made up of lipids and keratin (within epidermis)

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relatively impermeable to water loss in skin

water loss prevention: cocooning

amphibians/reptiles

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stops cutaneous water loss and wait out the driest parts of the year

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cocoon of mucus created

respiratory water loss

water loss that occurs through the lungs

urine/feces

contains nitrogenous waste products and ions (Na, K, Cl, bicarbonate)

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both leave through cloaca

ammonotelism

N to NH3

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in aquatic species: highly soluble and toxic

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least energy needed

ureotelism

urea soluble

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medium amount of energy needed

uricotelism

uric acid

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most energy needed

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insoluble

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get rid of N while conserving water

how do reptiles use salt glands to excrete excess ions

excess salt is secreted out and allows for water conservation

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salt in blood is filtered out through urine then goes back to blood

why do amphibians have to deal with short term changes in water balance

coqui frog

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has a water conservation posture when the night is dry: no vocalizing

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has a calling posture for wet nights where the frog can lose water: vocalizing

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postures help expose surface area and cut water loss in half

how do reptiles deal with water balance in the long term

plasma/urine solutes accumulate over time and the animal can tolerate high salt concentrations until water is available

where do sea snakes get fresh water from

sea snakes will go to the top of the ocean after rainfall, where there is a fresh water layer

heat gain equals…

heat loss

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heat moves on a gradient (high to low temperature)

Qabs

radiation absorbed by the surface of an animal

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behaviorally change amount of heat taken up:


1. neutral orientation
2. positive orientation
3. negative orientation
4. thermoregulatory changes in color

M

metabolic heat production

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large body size can do this and produce a higher amount than smaller body sizes (small component of overall total still)

R

infrared radiation received or emitted by the surface of an animal

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difference between temperatures of animal and rock (etc)

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based on area of animal exposed to thermal radiation

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matte surface: absorb IR

shiny surface: reflect IR

C

heat gained or lost by convection to the fluid (air or water) surrounding an animal (the fluid is air for a terrestrial animal and water for an aquatic animal)

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temperature difference between animal and medium (H2O, air)

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based on…


1. surface area (posture, body shape)
2. velocity of air movement
3. size of animal

LE

heat gained by condensation or lost by evaporation

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based on…


1. permeability of skin
2. humidity of air (more humid, more condensation)
3. rate of air movement (higher rate, more evaporation): cooling

G

heat gained or lost by conduction through direct physical contact of an animal with the substrate it is resting on (soil, rock, tree trunk, etc)

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temperature difference between animal and medium (rock)

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dependent on surface area of animal exposed to conduction (more contact, more heat movement)

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based on…


1. posture
2. body shape

heliothermy

heat gain by solar radiation

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texas horned lizard (ways to heat/cool down)

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andean toad: heat by clumping together and increasing their surface area

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some frogs inactive during day (absorbing heat) while others are active and have rapid hydration and cooling (small body size/quick)

thigmothermy

rely on conduction of heat from the substrate

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turtle embryos self thermoregulate in eggshells by tracking the position of the heat source and they follow it

kleptothermy

heat gain from the metabolic heat production of endotherms

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sea kraits sharing burrows with birds

what are set point temperatures

heliothermic and thigmothermic reptiles regulate their body temperatures between upper and lower set points

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window of temperatures (cold sensitive and heat sensitive)

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lizards:


1. too hot: move to colder area
2. too cold: more to warmer area

how do digestion and fever alter body temperature (set point temperature)

digestion increases body temperature

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fever increases body temperature

ex: lizards injected with dead and live bacteria, and after injection, body temperature was higher on average

how does heat transfer from the skin to the body core (3)

1. blood vessels in the skin dilate
2. heart rate increases
3. an intracardiac right to left (pulmonary to systemic) shunt increases the blood flow in the systemic (body) circulation

how do large reptiles generate metabolic heat (3)

1. muscular activity/contraction (leatherback sea turtle/snake)
2. digestion of animals (ex: jellyfish by leatherback)
3. increase metabolism in cold temperatures

how can reptiles vary in effectiveness of thermoregulation

thermoregulation vs thermoconformer

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thermoregulator sits just below set point range (more effective because there is a greater difference and more thermoregulation is done)

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thermoconformer sits within set point range

roughly how much water do reptiles and amphibians have in their bodies

65-85%

ambush posture (rain harvesting)

mojabi rattlesnake

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body rounded with head in striking position

rain collecting posture (rain harvesting)

“gutter” collects rain

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body flattened, channeling water into valleys, head between coils

water gain: water harvesting by reptiles (lizards specifically)

horn lizards, thorn devils

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water runs into channels and the lizard moves its mouth and draws water to mouth for drinking

water gain: water harvesting by reptiles (turtles specifically)

water follows the direction of the shell

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flows to bottom lip (marginal scutes) and travels to mouth

amphibians: pelvic patch

H2O channel in skin (aquaporin)

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channel opens and closes by AUT (argenine vasotocin)

amphibians: hold water in bladder

spadefoot toad spends 9 months underground

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bladder is full of dilute urine when entering ground

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urea remains stable for part of months because there is other H2O underground, but it increases in the next months because the water gets used up

where does water want to flow in fresh water

more solutes inside the animal

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water wants to go into animal

where does water want to flow in salt water

more solutes outside of animal

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water wants to flow out of animal

ectotherm

rely on external sources of heat

neutral orientation

positive orientation

allows for more heat absorption

negative orientation

allows for less heat absorption

thermoregulatory changes in color

melanin

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light object: reflect

dark object: absorb

cutaneous vasodilation

dilate blood vessels

aquatic reptiles and amphibians need to keep body temperature…

above water temperature

muscular thermogenesis

spasmodic contractions of the muscles

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generates heat

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when temperature is already warm, there is less contraction