Dealing with StressDealing with Stress

I. What is environmental stress?

II. Strategies for Dealing with Stress

III. Costs and Benefits

StressStress

•• StressStress is any condition that lowers the is any condition that lowers the performance or survival of an organism.performance or survival of an organism.

•• Most environmental factors are stressful if Most environmental factors are stressful if they are experienced in extremes.they are experienced in extremes.–– temperaturetemperature–– lightlight–– humidity/salinityhumidity/salinity–– pHpH

Dealing with StressDealing with Stress

•• Avoid stressful environmentsAvoid stressful environments

•• Adjust to stressful conditions Adjust to stressful conditions (acclimation or acclimatization) (acclimation or acclimatization)

•• Keep body conditions different Keep body conditions different from environmental conditionsfrom environmental conditions(regulation or homeostasis)(regulation or homeostasis)

Geographic Variation in Temperature

Huey & Stevenson (1979), Huey & Stevenson (1979), American ZoologistAmerican Zoologist

Per

form

ance

Temperature

Temperature as a StressorTemperature as a Stressor

AntarcticaAntarctica

Chaenocephalus aceratus

Life exists within a limited range of temperatures.Life exists within a limited range of temperatures.

Hochochka & Somero (2002), Hochochka & Somero (2002), Biochemical AdaptationBiochemical Adaptation

Per

form

ance

Temperature

Why is temperature stressful?Why is temperature stressful?

Molecules are too loose.

Molecules are too stiff.

Dealing with StressDealing with Stress

•• Avoid stressful environmentsAvoid stressful environments

•• Adjust to stressful conditions Adjust to stressful conditions (thermal acclimation) (thermal acclimation)

•• Keep body conditions different Keep body conditions different from environmental conditionsfrom environmental conditions(thermoregulation)(thermoregulation)

Molecules are like materials:Molecules are like materials:Some flex while other do notSome flex while other do not

Per

form

ance

Temperature

Organisms can acclimate to stress.Organisms can acclimate to stress.

Test Temperature (οC)

18 30

Num

ber o

f Cop

ulat

ions

0

1

2

3

4Acclimated at 18οCAcclimated at 30οC

Wilson and Johnston (2005),Wilson and Johnston (2005),In: In: Animals and EnvironmentsAnimals and Environments

Mosquito fish(Gambusia holbrooki)

Dealing with StressDealing with Stress

•• Avoid stressful environmentsAvoid stressful environments

•• Adjust to stressful conditions Adjust to stressful conditions (thermal acclimation) (thermal acclimation)

•• Keep body conditions different Keep body conditions different from environmental conditionsfrom environmental conditions(thermoregulation)(thermoregulation)

Geographic Variation in Temperature

Temperature varies greatly on a small scale.

M. W. Sears et al. (unpublished)

Mechanisms of Heat ExchangeOrganisms regulate heat exchange via behavior, morphology and physiology.

BEHAVIORBEHAVIOR

Organisms can moveOrganisms can movebetween sun and shade.between sun and shade.

sun

shade

MORPHOLOGYMORPHOLOGY

Color and posture influence heat exchange.Color and posture influence heat exchange.

Orienting the body away from Orienting the body away from the sun prevents overheating in the sun prevents overheating in plants and animals.plants and animals.

MORPHOLOGYMORPHOLOGY

Color and posture influence heat exchange.Color and posture influence heat exchange.

Collared lizards use dark bands Collared lizards use dark bands to absorb heat rapidly. Lizards to absorb heat rapidly. Lizards raised in colder environments raised in colder environments have more bands. have more bands. ((RandriamahazoRandriamahazo & Mori 2005)& Mori 2005)

PHYSIOLOGY

Blood flow can be used to gain or lose heat.

““ColdCold--bloodedblooded”” animals can animals can maintain a stable temperature.maintain a stable temperature.

Australian Lace MonitorAustralian Lace Monitor

Body Temperature (oC)10 14 18 22 26 30 34 38 42

Rel

ativ

e P

erfo

rman

ce (%

)

0

20

40

60

80

100sprint speedenduranceenergy assimilation

Angilletta et al. (2002),Angilletta et al. (2002),Journal of Thermal BiologyJournal of Thermal Biology

Body Temperature (oC)10 14 18 22 26 30 34 38 42

Rel

ativ

e P

erfo

rman

ce (%

)

0

20

40

60

80

100sprint speedenduranceenergy assimilation

Body tempsBody temps

Angilletta et al. (2002),Angilletta et al. (2002),Journal of Thermal BiologyJournal of Thermal Biology

EndothermyEndothermy

Endotherms increase metabolism at low temperatures.

Data for Pygmy Possumsfrom Bartholomew and Hudson (1962)

Met

abol

ic h

eat p

rodu

ctio

n

Insulation is needed for endothermy.

Dark regionis warmest.Tuna heat some parts

through endothermy.

Pythons use endothermy to heat their eggs.

Moths use endothermy to heat up before flight.

Endotherms often dump heat by evaporation.Endotherms often dump heat by evaporation.

Because water stores much heat, losing water to air Because water stores much heat, losing water to air removes heat from the body.removes heat from the body.

Mechanisms of ThermoregulationMechanisms of Thermoregulation

Decrease Heat LossDecrease Heat Loss::

-- constrict blood vesselsconstrict blood vessels-- raise pelageraise pelage-- reduce surface areareduce surface area-- increase blubberincrease blubber

Increase Heat ProductionIncrease Heat Production::

-- shivershiver-- voluntary activityvoluntary activity-- increase metabolismincrease metabolism

Increase Heat LossIncrease Heat Loss::

-- dilate blood vesselsdilate blood vessels-- sweatsweat-- pantpant

Decrease Heat ProductionDecrease Heat Production::

-- reduce activityreduce activity-- reduce metabolismreduce metabolism

EndothermsEndotherms:: most heat derived from metabolismmost heat derived from metabolism

EctothermsEctotherms:: most heat derived from environmentmost heat derived from environment

HomeothermsHomeotherms:: maintain a stable body temperaturemaintain a stable body temperature

PoikilothermsPoikilotherms:: let body temperature varylet body temperature vary

Poikilothermic ectothermPoikilothermic ectotherm-- plants, sessile terrestrial plants, sessile terrestrial organismsorganisms

Poikilothermic endothermPoikilothermic endotherm-- bats, bears, & other animals bats, bears, & other animals that undergo torpor or that undergo torpor or hibernationhibernation

Homeothermic ectothermHomeothermic ectotherm-- some reptiles and most fish some reptiles and most fish

Homeothermic endothermHomeothermic endotherm-- most mammals and birdsmost mammals and birds

Which strategy is best?Which strategy is best?

•• Depends on the costs of the strategy Depends on the costs of the strategy relative to its benefitsrelative to its benefits

•• Can you think of some costs of these Can you think of some costs of these strategies? strategies?

–– Thermal acclimationThermal acclimation–– ThermoregulationThermoregulation