E155 How are animals adapted to deserts?

What is a micro-climate, and what are some examples of micro-climates that help desert animals cope with heat?

• A localized set of climatic conditions that differ from the surrounding area

• Examples: shady areas, crevice in a cliff, under rocks, dens, burrows

How are animals hair or feathers modified for seasonal changes in temperature stress?

Decreasing the insulating value of feathers or fur 

Birds have advantages over mammals for heat

• Birds have higher body temp than mammals 

• Dilate blood vessels in their legs to dump excess body heat to the environment 

• Long ears of jackrabbits can transfer excess heat to the air through dilation of the blood vessels to the ear

What are some examples of evaporative cooling that are different from human sweating?

• Panting: abundant dilated blood vessels are near these surfaces and are cooled by them; cooled blood circulated throughout the body 

• Gular fluttering: owls flap the loose skin under its throat to move air over its mouth cavity 

• Energy efficient movements that produce very little heat themselves 

• Cooling in the nasal passages: cooling of a network of blood vessels to the brain in sheep, dogs, and cats 

• Urine: birds pee on themselves to cool down

What are sources of water?

• Free water: drinking from water holes 

• Water in food 

• Oxidation water: the water produced by all animals when they metabolize food

 How is water lost?

• Evaporative cooling 

• Dilution and excretion of toxic body wastes 

• Feces 

• Eggs or milk

Kangaroo rats don’t drink water. How do they get water from their environment?

• Water produced when food is metabolized (very small portion) 

• Dry seeds which, when stored in its burrow, absorb as much as 30% of their weight in water from the higher humidity in the burrow 

• Kangaroos have low evaporative loss

Would you describe humans as generalists or specialists? Why?

• Generalists, because performance varies across the species

The authors frequently mention the gradient between ambient temperature (T_a) and an animal’s body temperature (T_b). If T_a is higher than T_b, what are some possible coping strategies?

• Promotes heat gain from the environment 

• Tolerate an increase in Tb so the thermal differential is maintained at the minimum required to dissipate MHP passively 

• Regulate a relatively constant Tb by increasing the rate of heat loss (water evaporation) 

• Modify the rate of heat exchange between animal and its environment (rely on thermal inertia to keep Tb from increasing

It seems counter-intuitive, but an insulating layer can be a benefit for coping with heat stress. Why? (pg. 2171) 

• An insulating layer can absorb radiant energy near the surface, and allow some of the heat to be lost to the environment by conduction, convention, and radiation 

• Pelage: the insulating layer 

• An increase in the pelt thickness (decreased thermal conductance) and black coloration of a thermal shield can be beneficial 

What is a “thermal window”?

• Particular body surfaces can be specialized that promote heat loss by conduction, convection, or radiation to the environment 

• Examples: large ears of jack rabbits and elephants, relatively naked under surfaces and legs of camels, emus, and ostrich, and the bird bill 

anatomical adaptations for heat

• big ears = heat release

• dewlap = heat release

• wrinkled skin = hold extra H2O for evaporative cooling

• nasal turbinates = heat and H2O regulation with counter current exchange

anatomical adaptation in sahara ants

silves look reflects and dissipates heat to the surroundings

purpose of camels hump and feedback loop

hump is made of fat/ energy storage

• fat storage → B oxidation → H2O (not enough to be a source) and acetyl CoA → mitochondria → energy storage and production

when were the beetles most likely to climb on the ball

at higher soil temperatures bc the ball is cool

• thorax remains a stable tem

• tibia decrease in temp via conduction

• the ball impacts the soil beneath it too

example of convergent evolution

kangaroo rat and hopping mouse

where are the macula densa and granular cells located

inside the bowman’s capsule

purpose of macular densa and granular cells

pressure and osmolarity sensors in the capsule

where does aldosterone activity occur

distal tubule and collecting duct

where does counter current exchange occur

arterioles

where does filtration occur

bowmans capsule

where does H2O reabsorption occur

collecting duct, proximal tubule, distal tubules

where does reabsorption occur

proximal and distal tubules, collecting duct

where does secretion occur

prox and distal, collecting duct

where does ADH occur

collecting duct

how is glomerular filtration linked to BP

• macula densa cells sense flow, pressure, and NaCl/osmolarity

• send message to granular cells (sensitive to pressure and sympathetic NS) to secrete renin

renin

an enzyme involved in salt and water balance; BP control

autoregulation of glomerular filtration rate

maintains a nearly constant GFR when mean arterial blood pressure is between 80 and 180 mmHg

what happens at the proximal tubule

reabsorption: Na+, K+, Ca2+

secretion: metabolic drugs

low glucose and high Na+ inside tubule (both move outward into the cell via SGLT)

what does the loop of henle do

a counter current multiplier

• the blood moves in opposite direction of the filtrate

• descending loop = H2O reabsorbed to decrease osmolarity of blood going to the body

• ascending loop = reabsorbing Cl, Na, K into the blood leaving the body; no H2O out

what happens at the distal tubule

reabsorb HCO3, Na+, and H2O

secrete H+, K+, and aldosterone