Herps: Physiological Ecology (Water and Temperature)

- Animals are 70-80% water - Solute concentrations and location - Q10 effect - Temperature and water linked

Hyla arenicolor

Physiological Implications of the Environment

Increased temperature increased rate of chemical reactions

increased rate of metabolism

Q10 effects: Q10 = MR(t+10)

MRt

Q10 often = 2 to 3, depends on the two temps used

(Eckert 17-2)

Pough e

t al.,

20

01

Snake Example

Pough e

t al.,

20

01

Temperature and the Environment

(Eckert)

Herps: Physiological Ecology (Water and Temperature)

Behavior and Physiology altered by... ~ Amphibs to regulate water balance ~ Reptiles to regulate body temperature

Hyla arenicolor

- Behavior - Microhabitat - Posture - Color - Heart Rate - Blood Flow

Water

Get water: 1. liquid water

Amphibians- liquid water via skin

Pough et al., 2001

Pough et al., 2001

2. preformed water 3. metabolic water

Rana pipiens

Water

Osmolality (mosM = ‘milliosmoles’) concentration of solutes (in plasma or

urine) units are mmole solute/kg water 250 - 300 is about ‘normal’

Water moves from area of lower osmolality to area of higher osmolality

e.g., -soil to toad (or vice versa) -plasma to cell (or vice versa) -frog to ocean

Water

- Amphibs in fresh water steep gradient into body (2 mosM -> 250

mosM) produce lots of dilute urine

- Amphibs in salty water steep gradient out of body ( 500+ <- 250

mosM) therefore raise internal osmolality

(urea, sodium, chloride in plasma) (amino acids in muscle cells)

- Reptile skin relatively impermeable to water (lipids)

Water

Lose water: evaporation urine feces salt glands

Alter behavior and physiology to minimize water loss Water balance limits activity in time and space Amphibs lose most water via evaporation

- cutaneous resistance 1 dried mucus 2 cocoon 3 wax

Eleutherodactylus coqui Pough et al., 2001

Role of microhabitat

eyes

Pough et al., 2001

Phyllomedusa

More evap.

Less evap.

Pough et al., 2001

Chuckwalla

Monkey Tree FrogAnolis lizard

Alligator

Softshell Turtle

Bufo, Spadefoots, Rana

Water

(free water surface)

Urine from kidney - ions (sodium, potassium, chloride, bicarbonate) - nitrogenous waste (byproduct of protein digestion):

Water

1. ammonia - soluble but toxic

2. urea - very soluble and nontoxic - requires ATP and water

3. uric acid - insoluble - secreted as semisolid - conserve water

- reptiles, waterproof frogs Phyllomedusa (Hylidae), Chiromantis (Rhacophoridae)

- turtles and crocs can switch

Water

Dietary salts important (e.g., chuckwalla, desert

tortoise)

Salt gland - to excrete excess sodium and

potassium - conserve water, costs ATP

1. Lacrymal salt gland

sea turtles2. Lingual salt gland

crocodilians 3. Nasal salt gland

lizards

Shoemaker et al., 1992

Resistance to Evaporation - Cutaneous properties - Boundary layer (greater in larger animals) - Humidity - Wind Speed - Temperature

Shoemaker et al., 1992

Shoemaker et al., 1992

1 Humidity 2 Temperature

3 Body Size 4 Wind Speed

Behavior vs. Physiology

Shoemaker et al., 1992

Shoemaker et al., 1992

Non-arboreal

arboreal

Shoemaker et al., 1992

Morphological and physiological differences

Dorsal skin

Shoemaker et al., 1992

Cocoon Formation

Shoemaker et al., 1992

AVT (arginine vasotocin) -from posterior pituitary -stimulates water uptake -stimulates reabsorption from kidney and bladder

Pelvic patch -vascularization

Amphibians rarely ‘drink’

Shoemaker et al., 1992

Shoemaker et al., 1992

Nervous and Hormonal Control of water balance

Urine production

Blood Pressure

Sodium excretion

Shoemaker et al., 1992

Tolerance in salty water

Crab-eating frog

Larvae seem to excrete salt via gills (unique among amphibians in 930 mOsm NaCl)

Water Balance

Gopherus agassizii example Urine as a water reserve (16 months without H20)

Pough et al., 2001

Shoemaker et al., 1992

Larger animals have harder time getting enough O2 via skin

Gas exchange in lungless amphibians

Shoemaker et al., 1992

Use lungs to meet increased O2 demands

Gas exchange in amphibians

Temperature

Heat Gain (or loss)

Qabs = radiation absorbed by surface of animalM = metabolic heat production

R = infrared radiation received/emitted

C = convection to surrounding fluid (air/water)LE = condensation or evaporation

G = conduction (direct contact with substrate)

Temperature

Qabs = solar radiation absorbed by surface of animal

Pough et al., 2001

neutral

positive

negative

location - shade or sun posture - exposure

changes color - melanin in

melanophores of dermis

Temperature

M = metabolic heat production chemical energy ‘lost’ as heat during metabolism

Pough et al., 2001

large species can use to be somewhat endothermic

- surface area to volume ratio - leatherback (Dermochelys coriacea) - pythons (female brooding clutch)

Temperature

R = infrared radiation received/emitted surfaces emit and receive infrared (thermal) radiation

Callisaurus draconoides

smooth

matte

-not related to color, but texture instead matte - absorb and emit well

smooth - absorb and emit poorly

Temperature

C = convection to surrounding fluid (air/water) - fluid movement takes heat away

lizard climb bush midday

Sauromalus ater Sceloporu

s occidental

is

- body size and boundary layer small - feel changes more quickly large - less influenced by convection

Temperature

LE = evaporation (or condensation) Evap. cooling not typically important for reptiles

- some pant if overheated Amphibians

- lots of evaporation

G = conduction (direct contact with substrate) transfer between touching objects

ventral surface on warm rocks aquatic herps typically same temperature as water

Thermoregulation

Temperature Set Point (often a narrow range) alter by season gravidity infection

Hypothalamus

Heliothermic vs. Thermoconformers Pough et al., 2001

Body temperature & thermoregulation

I. Ectotherms

II. ThermoregulationA. Temperature Regulation

B. Reptiles v. Amphibians

III. Controlling Body Temp.

I. Ectotherms: all physiological processes are temperature dependent

Temperature and Performance

• Effective escape

• Development

II. Thermoregulation

• Temperature

• Ectothermy – limits options

• Metabolic heat –

• Temperature range

Hypothalamus – temp. control

• Set point temp. or set point range regulation control center

• Sensor in hypothalamus integrates info about the temp. of the body, via blood flow

Ectotherm temp. profile -

Min. Max.

A. Temperature Regulation

• Heat gained = heat lost (steady state)• Heat energy gained

– Qabs = radiation absorbed by the surface– M = metabolic heat production– R = infrared radiation received/emitted– C = Heat gained/lost by convection– LE = Heat gained by condensation or lost by

evaporation– G = Heat gained/lost by conduction

Body color can affect

1. Adjusting convective heat exchange

2. Body size affects thermoregulation

• Surface area • Heat gain/loss rate

decreases as body size increases

Large leatherback turtles: inertial endothermsAble to retain metabolic heat in addition to generating heat from muscle activity

B. Reptiles v. amphibians-

1) Permeable skin –big challenge

• Evaporative cooling to balance effect of solar heating– Ventral surface next to wet

substrate to replace water lost via evaporation

• Selection of suitable microhabitat

2) Impermeable skin – also challenging

• Panting,

III. Controlling body temp (maintaining body temp. different from ambient temp.)

1) Behavior

2) Short term

3) Microhabitat selection

4) Water absorption & evaporative water loss to moderate temperatures

5) Heat production

Cardiovascular control of heating/cooling

Circulatory adjustments

1) Higher heart rate during heating

2) Intracardiac shunt

3) Blood vessel dilation

Acclimation, Recent History of Individual “Reset” Metabolism

(Eckert 17-3)

Seasonal or ontogenetic differences

Thermoregulation

Cardiovascular control of heating and cooling

- Cardiac Shunts

- Peripheral Vasodilation

Pough et al., 2001

Pough et al., 2001

Thermoregulation

Freezing - ice crystal formation alter osmolality physical destruction

1. Freeze Resistance supercool prevent ice crystals (Sceloporus jarrovii) (Chrysemys picta)

2. Freeze Tolerance (Rana sylvatica ) glucose or glycerol as antifreeze in cells

Pough et al., 2001

How do they work?

- RESPIRATION (gas exchange) - CARDIOVASCULAR SYSTEM - METABOLISM

novel systems, structures, behaviors, habitats...

Respiration

- Bring in Oxygen (and get it to the tissues)

- Get rid of Carbon Dioxide (and control blood pH)

Gas Exchange - into solution - water balance...

Respiration

- in AIR

- in WATER

Reptiles mostly air, Amphibs often both

1. Pulmonary - lungs

2. Non-Pulmonary - skin surface, gills, pharynx, cloaca

Respiration (non-pulmonary)

Amphibians

- gas exchange/water balance - buccal region

Plethodontids: skin + buccal - skin folds, highly vascularized

water needs to be moving e.g., Hellbender, Lake Titicaca frog

- Male Hairy Frog (Trichobatrachus robustus) breeding season gets skin filaments -

why?

Cryptobranchus

Reptiles - drier skin - lipid layers to retard water

loss - less cutaneous gas

exchange -BUT, some aquatics…

Hydrophiinae (sea snakes) cutaneous respiration

Chelonia many with gas exchange at

pharynx or cloaca e.g., Pleurodiran Rheodytes

leukops (Australia) - bursae from cloaca

lined with villi - pump water in and out

bursae 80x/min

Hydrophis melanocephalus

Respiration (non-pulmonary)

Respiration (Pulmonary)

gills useless in air - so developed lungs...

Buccal Pumping (Positive-Pressure Ventilation) - ancestral tetrapod trait - amphibians use exclusively, reptiles

sometimes

e.g., Sauromalus ater inflate lungs for defense

How it works… 1. Close glottis, open nostrils, lower buccal floor

- air into mouth 2. Open glottis valves, nostrils still open, buccal floor low

- air out of lungs, passes over new air, leaves nostrils 3. Glottis still open, close nostrils, raise buccal floor

- positive pressure pushes air into lungs Repeat

Aspiration (Negative-Pressure Ventilation) - reptiles use to breathe - expand thoracic cavity, creating vacuum

Lepidosaurs (lizards, snakes, tuataras) inhalation - internal and external intercostals

contract relaxation - lungs inflated, glottis closed exhalation - hypaxial contraction (~ventral)

Some species can’t breathe and locomote others use gular to force air into lungs e.g., Varanidae

Respiration (Pulmonary)

LUNGS - vary from simple sacs to complex Amphibs:

generally simple more complex in frog than salamander

(more surface area too) Reptiles:

paired ancestrally reduction or loss in elongate forms e.g., snakes with reduced left lung lung complexity correlated with activity in

lizards turtles and crocodylians with multi-chambered

lungs

Respiration (Pulmonary)

Snakes right lung with two parts 1. vascular

anterior and chambered, lots of blood vessels

2. saccular posterior, no chambers regulates airflow buoyancy in marine groups (~ to cloaca!)

Respiration (Pulmonary)

Pough et al., 2001 Fig 6-6

Crocodylians liver as plunger to compress and expand lungs instead of trunk musculature liver and lung linked by connective tissue exhalation liver pulled anteriorly by abdominal muscles inhalation liver pulled posteriorly by diaphragmaticus

muscles that attach to pelvis

Respiration (Pulmonary)

Turtles modified because of shell exhalation

- force viscera up against lungs inhalation

- increase vol. of visceral cavity so lungs expand

Respiration (Pulmonary)

inhale

inhale

exhale

exhale

Pough et al., 2001 Fig 6-7

EGGS crocs and many turtles

- calcified shell - pores in calcium crystalline structure

lepidosaurs and some turtles - flexible fibrous shell - diffusion of gases through fiber gaps

Respiration

circulatory system heart, vessels, blood move O2 and CO2

Cardiovascular System

gills simple: 1. Blood goes to gills 2. O2-rich blood goes to tissues 3. O2-poor blood goes to heart 4. Blood gets pumped back to gills

lungs more complex because get 2 circuits in parallel:

1. Pulmonary circuit (lower pressure) 2. Systemic circuit (higher pressure)

Herps (except crocs) with 3 chambers (= one ventricle)

- no ventricular septum - BUT separate rich and poor blood - AND alter pressure in systemic and

pulmonary

Cardiovascular System

Amphibians only vertebrates where O2 poor blood to skin

(as well as to lungs) adults with paired pulmocutaneous arteries

divide into two branches 1. Pulmonary 2. Cutaneous (to flanks and dorsum)

skin provides 20-90% O2 uptake 30-100% CO2 release

Cardiovascular System

Anuran Heart conus arteriosus w/ spiral valve trabeculae (create channels) role of Tb and HR (in separation)

Cardiovascular System

Pough et al., 2001 Fig 6-8

Gets poor

Gets rich

rich in

Squamate Heart (and turtles) (no conus arteriosus, no spiral valve) 2 systemic arches and one pulmonary artery from single ventricle BUT, single ventricle functions as THREE 3-chambered heart anatomically 5-chambered heart functionally

Cardiovascular System

RAA = right aortic arch LAA = left aortic arch PA = pulmonary artery

Muscular Ridge

Pough et al., 2001 Fig 6-9a

RA = right atrium LA = left atrium

rich

Pough et al., 2001 Fig 6-9

Squamate Heart (and turtles) not “primitive”

RAA = right aortic arch LAA = left aortic arch PA = pulmonary artery

Muscular Ridge

CP = cavum pulmonale CV = cavum venosum CA = cavum arteriosum

IVC = intraventricular canal AVV = atrioventricular valve

1

22

1

3

4

4

55

6

77rich

rich

Cardiac Shunts R to L

O2 poor to systemic via aortic arches (short delay between valves opening)

L to R O2 rich to pulmonary artery (longer delay between valves opening)

Cardiovascular System

1. temperature regulation 2. breath holding (diving, turtle in shell, inflated lizards) 3. stabilize O2 content of blood when breathe intermittently

pulmonary then aortic

Crocodylians (different!) 4-chambered heart - normally right to left shunt

e.g., at rest

Cardiovascular System

Pough et al., 2001 Fig 6-10

(shown in use)

BUT have foramen of panizza allows blood from left ventricle to get to the left aorta when left ventricular pressure is

high (thereby closing right ventricular valve) e.g., when diving

rich

right ventricular valve

Shared Characteristics of Amphibians/Reptiles

• Ectothermy– Mammals, birds are endothermic.

• Body temp is maintained at most efficient level for maximum performance.

• Body size, shape

METABOLISM

Herps are Ectothermic

- source of body heat is sun, rather than metabolism - still regulate body temperature (Tb) rather precisely

Pou

gh

et

al., 2

00

1

Herps are Ectothermic

lizard uses 3% of energy of similar-sized mammal: 1. ~1/10 the metabolic requirements at a given Tb 2. Let Tb decrease at night 3. Overall lower activity than mammals Implications for production vs. maintenance

Pough et al., 2001

Ectothermic Amphibians, Reptiles

• Control body temp within narrow limits during active periods.– Warms up from direct sunlight (basking),

sitting on warm substrate– Cools in shade

Thermoregulation of desert iguana

Night: 20oC Day: up to 42oC

Advantages of Ectothermy• Uses less energy to maintain same body

temp as squirrel of same size.

• Drop in body temp at night conserves energy even more.

• Less active than endotherm; even less use of energy.

• Requires less food.

Metabolic Rates of Ectotherms/Endotherms

Mass-specific energy use: MR of endotherms is 7-10x that of ectotherms.

Effect of Body Temp on Activities of Ectotherms

Disadvantages of ecto?Escape?Vulnerability at night?Activities in winter?

Impact of Ectothermy and Endothermy on Ecosystem

• Study of Hubbard Brook experimental forest in NH:– Salamanders consumed food worth 46,000kJ/hectare– Birds consumed 209,000kJ/hectare.– Conversion efficiency of salamanders is 60%; birds <

2%. Sal. provide much more energy to food chain than birds.

– Small salamanders eat small prey that is not available to larger endotherms.

Ectothermic Metabolism

Pough et al., 2001

Energy (ATP = adenosine triphosphate)

Metabolism

Activity... ATP, then Phosphocreatine (30 sec) then need to synthesize ATP:

1. Oxidative/Aerobic 1 CHO -> 35 ATP (+ CO2 and H20) efficient but slow (sustained)

2. Glycolytic/Anaerobic 1 CHO -> 3 ATP (+ lactic acid) rapid but inefficient (burst)

Oxidative vs. Glycolytic

Metabolism

Muscles (or parts thereof) specialized to be either oxidative or glycolytic - Anuran calling (males)

muscles hypertrophy in breeding season - Locomotion example...

How measure: 1. Oxidative metabolism - oxygen consumption 2. Glycolysis - lactic acid production

Twitch Speed (SPRINTING) Oxidative Capacity (ENDURANCE)

1. FG = Fast Glycolytic 2. FOG = Fast-Oxidative Glycolytic 3. SO = Slow Oxidative

Muscle Fiber-Types

Iliofibularis muscle

Iliofibularis Muscle (IF) cross-section with darker oxidative core that appears red in fresh tissue

Dorsal view of lizard hindlimb

IF

Histochemistry

More sustained contractions

Greater force production

Femur

Cross Section of Hindlimb at

Mid-Thigh

Histochemistry

IF

Iliofibularis Muscle (IF)

Succinic Dehydrogenase

(SDH)

His

toch

emis

try

Myosin ATPase

Fast Twitch (~Glycolytic)

Aerobic Capacity

mATPase (fast-twitch)

SDH (oxidative)

SO (slow-oxidative; light mATPase,

dark SDH)

FG

(fast-twitch glycolytic; dark

mATPase, light SDH)

FOG

(fast-twitch oxidative

glycolytic; dark mATPase and

dark SDH)

Fiber-Type Histochemistry

- -

Uta stansburiana

Sceloporus magister

Sceloporus undulatus

Sceloporus virgatus

Uma notata

Callisaurus draconoides

Cophosaurus texanus

Holbrookia maculata

Phrynosoma cornutum

Phrynosoma modestum

Phrynosoma mcallii

Sceloporus

Group

Sand

Horned

11 Species of Phrynosomatinae

0

10

20

30

40

50

60

70

80

1 10 100

Body Mass (g)

% F

as

t-G

lyc

oly

tic

0

10

20

30

40

50

60

70

80

1 10 100

Body Mass (g)

% S

low

-Ox

ida

tiv

e

Iliofibularis FG and FOG compositions vary among phrynosomatine subclades; composition of SO fibers does not vary

Scelop. Group Sand Lizards Horned Lizards

% F

ast

Gly

coly

tic

(FG

)

% S

low

Oxi

dat

ive

(SO

)

ANCOVA conventional P < 0.001 phylogenetic P < 0.005

Speed predictors across lizard taxa

r2 = 0.899 p < 0.0001

Metabolism

Locomotion in Herps - good burst performance - poor endurance

(Varanidae, Teiidae exceptions)

- often intermittent increases total distance before fatigue

- snake modes have different costs concertina>lateral>sidewinding

Pough et al., 2001 Fig 6-15

Metabolism

Glycolytic metabolism - [lactate] can increase 20x

(~ = fatigue) - egg-laying - territorial defense - locomotion (80% sprint ATP) - prey swallowing - first 30 sec of activity

compared to mammals, herps have ~10x lower aerobic capacity

BUT, herps achieve equivalent burst capacity and, better able to reconvert lactate to glycogen

Pough et al., 2001 Fig 6-13

Metabolism

1. Standard postabsorptive, inactive, inactive part

of day

Metabolic Rates

2. Resting postabsorptive, inactive, active part of

day usually 10% greater than standard

3. Maximum e.g. maximum aerobic speed beyond that speed need to use

glycolysis (intermittent)

Metabolism

Pough et al., 2001 Fig 6-11

- standard

- resting

~max

Metabolism Anuran Vocalizations - male calling is hardest work he does

- same amount of noise energy as bird 10x larger- VO2 25x that of resting rates (higher than jumping)

- anatomical and biochemical specializations trunk muscles hypertrophy

% body mass corr. with calling effort highly oxidative

mitochondria, capillaries, oxidative enzymes

- lipid if call a lot, glycogen if don’t call as much

- reserve depletion, weight loss, few nights then recuperate

Pough et al., 2001 Fig 6-18

Mating success correlated with - call rate - chorus tenure

Metabolism Egg Development - TSD for some reptiles

- embryos metabolize yolk 1. Maintenance and growth 2. Fat storage (temperature and moisture determine allocation)

- in general, wetter egg means larger hatchling because more yolk is metabolized

- larger hatchlings likely have higher fitness (~faster locomotion)

Turtle Hatchlings

Pough et al., 2001