Announcements Exam next week (Tuesday)! Will cover material

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Announcements

• Exam next week (Tuesday)!
• Will cover material through this Thursday
• Review session
• WHAT TIMES WORK?
• Thursday eve?
• Monday eve?
• Exam format 100 points
• Some short answer questions
• Mostly will be longer answer questions

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Pop Quiz 1

• Quiz mean 7.5/10 and SD 1.5
• Copies are available if you missed it and need a
  study tool
• Format similar to exam
• Longer answer questions will be for more points!
• TIPS Read the question and make sure you do
  everything that was asked!

students
Grade
E.g. Use Ficks Law This means Ficks Law
needs to be in your answer somewhere!
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Heat exchange exercise

• You guys did good!!!
• Picky stuff
• Conduction requires CONTACT
• Some of you cited d as the distance between an
  animal and a given surface this is incorrect!
• d thickness of contact surface
• Some of you cited temperature difference
• Was it affected by animals behaviors?

4
Strategies for enhancing evaporation
Does not waste body water!
Uses body water!!
5
Fog basking
Namibian tenebrionid Onymacris unguicularis Stran
ge pre-dawn behavior on coastal dunes Collects
water that condenses from fog
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Thermal physiology (2)

• Heat flux summarized
• Temperature effects on reaction rates
• Q10 effect
• Temperature effects on membranes
• Homeoviscous adaptation
• Acclimation and thermal tolerance
• Surviving freezing temperatures

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Clarifying reading

• Schmidt-Nielsen temperature readings
• Last class page 242-254 (beginning of chapter 7)
• This class 218 238 (chapter 6)

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Total heat flux into/out of animal
Operative temperature environmental temperature
experienced by an animal Determined by a
particular microhabitat Flux due to conduction,
convection and radiation Measured with
conductive animal models and thermocouples Contra
st this with Ambient Temperature air
temperature Doesnt take wind or radiation into
account
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Total heat flux into/out of animal
e.g. camels and some desert ungulates Allow
Tbody to rise by a few degrees on hot days heat
storage Rather than using evaporation to keep
it constant Strategy for water conservation!
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Thermal tolerance

• The WIDTH of the range of temperatures animals
  can withstand ranges widely among taxa
• High and low temperatures at which mortality
  occur
• Upper critical temperature
• Lower critical temperature
• Even when an animal is within its tolerated
  temperature range, activity may be severely
  impacted by high and low temps.

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Temperature affects biochemistry profoundly
Reaction rate
Temperature
Reaction rates increase with increasing
temperature
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Measuring temperature sensitivity Q10
Increase in rate caused by 10 increase in
temperature
IF Q10 2, rate doubles for every 10 degree temp
increase
T2-T1 10
RT2 RT1 ? Q10
Rearranged
IF Q10 3, rate triples for every 10 degree temp
increase
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Q10 varies, but is often 2 - 3 in living animals
Process Q10 Diffusion 1.03 Oxygen
consumption in beetle (10 deg) 2.4 (20
deg) 2.1 Crayfish heart rate (5
deg) 2.4 (15 deg) 1.6 Hemoglobin
coagulation 13.8!!!
However Not always consistent across all
temperatures
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O2 consumption rate in Colorado potato beetles
Schmidt-Nielsen 1997
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Q Why do reaction rates drop off at high
temperature?
A Enzyme starts to fall apart!
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Many biological reactions have optima
thermal denaturation protein falls apart
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Even poikilotherms have thermal optima!

• Below optimum, reactions are slowed
• Above optimum, risk of heat death
• Thermal denaturation of proteins?
• Membrane structure is compromised?
• Rate effects on pathways throws metabolism out of
  whack?
• This can happen at seemingly very low
  temperatures
• E.g. 4-6 ºC in Antarctic fish!
• Terrestrial ectotherms will seek shade or sun to
  maintain body temperature at optimum

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Temperature affects membrane fluidity
-- this effect can be counteracted by composition
of membrane phospholipid bilayer!
Saturated fatty acids Hydrocarbon chains have
single bonds only These pack together
tightly Decrease fluidity of membranes Think
butter
Unsaturated fatty acids Hydrocarbon tails have
one or more double bond These pack much less
tightly Increase fluidity of membranes Think
vegetable oil
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Homeoviscous adaptation (HVA)
As temp membrane fluidity . This can
be counteracted by an increase in unsaturated FAs
Animals that routinely live at low body
temperatures tend to have more unsaturated fatty
acids in membranes
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Homeoviscous acclimation
Animals can control membrane composition in the
short term
How?
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Acclimation

• Compensatory physiological change within an
  animals lifetime
• In field/seasonal conditions acclimatization
  
• (usually a suite of factors changing)
• Wide variation among species in their acclimatory
  ability
• A lot of that variation has to do with how much
  variation the animal typically encounters in
  their environment
• Important prefixes
• Steno only can cope with a narrow range
• Eury able to cope with a wide range

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Temperature Acclimatization
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Thermal tolerance polygonsa way to characterize
a species ability to acclimate
Tolerated temperature range critical
temperatures
Acclimation temperature
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Thermal tolerance polygons
Goldfish Very temp tolerant eurythermal
Tolerated temperature range critical
temperatures
Puffer fish Moderately stenothermal
Antarctic perch Very temp intolerant
stenothermal
Acclimation temperature
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Surviving freezing temperatures
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To freeze or not to freeze?

• Freezing is dangerous due to
• ice crystal formation (ice is sharp!)
• Dehydration (all your water gets bound up in
  ice!)
• Two main strategies
• Freeze avoiders
• Prevent ice formation
• Do NOT tolerate freezing
• Freeze tolerators
• Control ice formation
• Tolerate partial to near total freezing

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What makes a solution freeze?
1) Temperature 2) Time 3) Presence of nuclei
Ice crystallization needs a little help Very
pure water will freeze at -20ºC!
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Important principles properties of water
1) Molecules in solution (solutes) decrease the
freezing point of water (-1.86ºC for every mol/L
of solute).
Colligative property of water
Sugars, salts, amino acids
Commonly are polyhydric alcohols glycerol,
sorbitol
2) Ice crystals form more easily when they have
particles or nuclei to form on (a.k.a.
nucleating agents)
These are often ice crystals but can also
be particles e.g., digesta in the
gut proteins e.g. nucleating proteins
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Freeze avoiders have low freezing points

• Produce lots of colligative antifreeze
• Synthesize antifreeze proteins
• Specialized response need to evolved the genes
  for these!
• Avoid ice nucleators
• Purge guts
• Spin cocoons to protect themselves from ice

Gall moth Epiblema scudderiana Freezes at -40 to
-50ºC!
Pro avoid freezing Con If they do freeze, it is
very rapid and uncontrolled
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Freeze tolerators control freezing

• Produce ice nucleating proteins in extracellular
  fluid to encourage controlled ice formation
• Use antifreeze to control ice growth
• Use antifreeze compounds inside cells
• Stabilize membranes with sugars and amino acids

e.g. Rana sylvatica wood frog Tolerates over
60 of body water freezing! Manufactures huge
quantities of glucose Selectively allows organ
dehydration
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Antifreeze proteins are more effective than
solutes
However, you dont need a special gene to produce
sugar or glycerol
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Antifreeze proteins
ala
ala
thr

• Antifreeze glycoproteins (AFGPS)
• All have 3 amino acid repeats
• thr-ala-ala
• trimers make a helical repeat of just the right
  size.
• Stop development of ice crystals by binding to
  crystal edge!

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Cool story of convergenceAntifreeze proteins in
arctic/antarctic fish
Arctic cods
Different superorders!
Antarctic nototheniods
Chen et al 1997 PNAS 94 3817-3822
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AFGPs have different origins!
AFGPs modified from trypsinogen - a protease
produced by the pancreas! Now also produced by
liver
Antarctic nototheniods
Molecular clock suggests divergence of two genes
5-14 mya Antarctic ocean cooled to freezing
mid-Miocene 10-15 mya
????? Dont know where AFGP came from (but not
trypsinogen!)
Chen et al 1997 PNAS 94 3811 - 3816
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This weeks IAB seminar
Antifreeze proteins and overwintering strategies
in insects
Jack Duman Notre Dame
Friday, 330 pm Elvey Auditorium