Physiological Ecology Water and Salt Balance Respiratory Gas Exchange Respiration and Metabolism Thermoregulation Dormancy Energetics
Importance Amphibians and reptile physiology is directly tied to the environment Often diel or seasonal fluctuations in environmental temperature can impact or constrain physiological process Cooler temperature Dormancy Reduced locomotor performance Reduced digestive performance Why we don t see many amphibians and reptiles in cold climates
Physiological Ecology Water and Salt Balance Respiratory Gas Exchange Respiration and Metabolism Thermoregulation Dormancy Energetics
Water Balance Amphibians and reptiles are composed of 70 80% water A suit of different tactics to maintain water and salt balance (Homeostasis) Water loss Marine habitats Terrestrial habitats Water gain Fresh water habitats
How Water is Lost in Herps Excretion Feces Urine Salt glands Respiration Integument Amphibians are more sensitive to water loss Permeable integument But can uptake water as well Reptiles Lose mainly through excretion and respiration Species occupying xeric habitats have evolved interesting adaptations
Combating Water Loss Postures Waxes Cocoons Skin Closing shell (Turtles) Retention (Specialized Structures) Phyllomedusa sauvagei waterproof frog
Postures Some species of frogs will attempt to reduce their surface area This is achieved by basically curling up A reduced surface are for amphibians means a reduced potential for water loss White-lined Leaf frog (Phyllomedusa vailllanti)
Waxes Maki Frog (Phyllomedusa tomopterna) The waxy frogs have specialized secretions Secrete lipids with wax esters Behaviorally spread the wax Reduces water loss at temperatures < 35 C Waxes break down However, those temperatures only occur during the rainy season Thus, the chance of desiccating is minimal
Cocoons Found in several frog taxa as well as sirens Formed from multiple skin shedding events Opens only at nares to allow for breathing Water holding Frog (Cylorana platycephala) Common Siren (Siren lacertina)
Specialized Amphibian Skin Variable skin permiability Protein/lipid layers Addition of more iridophores during dry season More radiation reflection Hyperolius viridiflavus
The Turtle Shell Ornate Box Turtle (Terrepene ornata) An effective water loss barrier Esp. effective for species which can completely enclose themselves
Cloacal Bursae Small sacs surrounded by thin membrane Can contribute to uptake of water, as well as gas exchange Cloacal bursae of turtles
How is Water Gained? Drinking Eating Absorption through skin Metabolism
Uptake Through Amphibian Skin Red-Spotted Toad (Bufo punctatus) Thin smooth ventral sufaces Inner thigh patch very thin and highly vascularized Cutaneous uptake hormonally regulated
Uptake Through Reptile Skin?? Correct posturing can funnel water through channels between scales Exposed skin between scales can contribute to water uptake Thorny Devil (Moloch horridus) Round-tailed Horned Lizard (Phrynosoma modestum)
Kidney Function Amphibian urine usually more dilute Structure slightly different between amphibs and reptiles function the same
Nitrogen Excretion Rana catesbeiana tadpole Xenopus Ambytsoma tigriunum Ammonia (ammonotelic) Primarily aquatic animals Small molecule Diffuses across gills Highly toxic Urea (ureotelic) Mainly amphibians All terrestrial species Less toxic Uric Acid (uricotelic) Most snakes and lizards Requires little water for excretion Serves to conserve water Gambelia spp
Specialized Salt Glands Glands in different places to expel salt Turtle gland homologous to lacrimal salt glands of birds
Salt Glands in Lizards, Crocodilians, and Turtles Marine Iguana Nasal glands True of all lizards Actually shoot the salt out Crocodilians Lingual Turtles Lacrimal Why sea turtles cry when nesting Marine Iguana (Amblyrhynchus cristatus) Green Sea Turtle (Chelonia mydas) Oh yes, tears of joy.
Amphibian Tolerating Brackish Water Remain in osmotic balance by tolerating a high level of urea in blood Rana cancrivora inhabits estuaries in SE Asia
Desert Tortoise Store water in bladder Lose as much as 40% of mass during drought Volume of total body water reduced to 60% Bladder holds high solute levels Solute levels in plasma increase with increasing dehydration (anhomeostasis) Anhomeostasis
Physiological Ecology Water and Salt Balance Respiratory Gas Exchange Respiration and Metabolism Thermoregulation Dormancy Energetic
Respiration 101 Uptake of O 2, excretion of CO 2 External Respiration Transfer of oxygen to from the environment to the blood Internal Respiration Gas exchange between the blood and cells Respiration in Water Energetically costs Low concentration of O 2 in water Respiration in air Less energetically costs Higher concentration of O 2 in air
Larval amphibians Neotenic forms Evaginated respiratory surfaces Strictly an aquatic structure Lentic habitats Move gills back and forth Buccal pump over gills Larger feathery gills Lotic habitats Let the water run over the gills Smaller stouter gills Gills
Buccal Cavity and Pharynx Florida Softshell (Apalone ferox) A small percentage of gas exchange The membranes in the mouth are permeable to O 2 and CO 2 Can be significant in species that remain submerged for long periods Important for species that hibernate submerged
Cutaneous Respiration Most important for amphibians Diffusion Highly vascularized skin by capillaries Enhanced by increasing surface area with folds (Cryptobranchus and Telmatobius) Open bars oxygen uptake Yellow carbon dioxide excretion
Lungs Main mode for terrestrial herps Amphibians use a buccal pumping Reptiles thoracic aspiration Snakes Left lung reduced only occur in the anterior portion Right lung fully functional
Physiological Ecology Water and Salt Balance Respiratory Gas Exchange Respiration and Metabolism Thermoregulation Dormancy Energetics
Hibernation Physiology of Turtles Ultsch et al., 1985 Mobilize Calcium and magnesium Ions to preserve electroneutrality Extra pulmonary avenues to reduce of CO 2 excretion to reduce respiratory acidosis Mobilize free ions to combat lactate acidosis How well a turtle does this can dictate how far north in latitude it will range
Physiological Ecology Water and Salt Balance Respiratory Gas Exchange Respiration and Metabolism Thermoregulation Dormancy Energetics
Importance of Temperature Physiological processes are tied to temperature Too cold slowed performance No herps in Antarctica Too hot slowed performance Desert reptiles must even beat the heat Must thermoregulate HOT, HOT, HOT!!!!
All These Thermys Poikliothermy Wide variation in body temp with respect to the environment Homeothermy Constant body temperature even with great environmental temperature fluctuations Ectothermy External temperature is the main source of heat Endothermy Internal production is the main source of heat, primarily metabolic heat Heliothermy Heat gain from the sun Thigmothermy Heat gain via conduction from apposition with an object Gigantothermy Heat is retained because of a low surface area to volume ratio, a large organism can retain more heat
Here Comes the Sun! Ultimate heat source Directly Conduction Indirectly Convection Temperature is carefully regulated Mainly behaviorally Amphibians Active at cooler temperatures because of water loss Reptiles Relatively impermeable skin allows them to be more active
All herps operate around a thermal set point This is the range of temperatures at which the organism begins to thermoregulate Controlled by the hypothalamus Acts as a thermostat to trigger behavioral thermoregulation Thermal Set Point
Thermal Minima and Maxima Preferred Temperature range selected by individuals in a thermal gradient with all other factors controlled for Activity Range the range at which normal activity occurs Voluntary the lowest and highest temperatures tolerated by the organism Critical at the low temperatures produces cold narcosis and at the high temp animal cannot control itself, in both cases locomotor and escape ability is impaired and the organism cannot escape the low or high temperature Lethal the low and high temperatures which produce death.
Environmental Heat Exchange Occurs via Radiation Convection Conduction Terrestrial and arboreal Reflected solar radiation Heat of air Heat of substrate Aquatic Reflected solar radiation Heat of water Subterranean Conduction Heat from the surrounding soil Underside of warm surfaces All behaviorally regulated For small herps Physiological control of heat minimal At best only evaporative cooling mechanisms
Heat Exchange - Lizard
Heat Exchange - Others
Factors Affecting the Activity Range
Controlling Performance Temperature drastically affects performance Within what is voluntarily tolerable there is an optimal temperature This is where performance is the highest
Rana clamitans Jumping distance Shorter distance above 25 C and below 10 C Longer distance between Better able to escape predators
Thamnophis elegans Numerous relationships in Thamnophis elegans Oxygen consumption Digestion Speed Strike Velocity Tongue Flicking Rate Growth Rates
Cascading Effects Eggs to Performance Two temperature regimes 20 C cold 27 C hot Hot incubated eggs ran faster at higher body temperatures This gain was observed over the entire study
Thermoregulation You are just gonna take me across right?? Maintenance of a relatively constant body temperature even through varying environmental temperatures Amphibians and reptiles do this in a myriad of ways Primarily behaviorally driven
Control often involves diel shifts These shifts can be behavioral adjustments or even different choices of microhabitat Peter s Lava Lizard (Tropidurus hispidus) Use warmer rocks in the morning to gain heat Use cooler rocks in the afternoon to maintain temps Shifting Patterns
Precision of Maintenance Many herps can regulate their body temperatures higher than the environment The Crested Anole at higher altitudes Maintain a higher temp Even during relatively cooler months
Leatherback Sea Turtle Approaches endothermy Can maintain a body temperature of 25 26 C in 8 C water Does this by: Countercurrent heat Exchange Elevated metabolism Thick oil filled skin Darkened coloration Internal Heat Gain
Egg Brooding Pythons Female Burmese Pythons will contract muscles while brooding Some heat in transferred to the eggs and enhance development During brooding the female can maintain a relatively high body temperature Oxygen consumption increases during this phase (yellow bars)
Costs of Thermoregulation Individuals may not maintain optimum temperatures Predation risk Environment where thermoregulation is difficult Costs of not thermoregulating Predation risk Reduced performance Reduced foraging
Sub-optimal Selection Galapagos Land Iguanas Choose slightly cooler environments So they can remain active for longer periods during the cooler season
Physiological Ecology Water and Salt Balance Respiratory Gas Exchange Respiration and Metabolism Thermoregulation Dormancy Energetics
Importance of Dormancy Must go dormant when environmental conditions are sever Preserve homeostasis Extremely dry conditions Temperatures out of tolerable ranges Can remain dormant for considerable portions of the year Parsed into Hibernation Escape extremely cold condition Metabolic activities are suppressed Altered cardiovascular function Aestivation Typically extreme heat or drought Metabolic rates are slower Water loss rates variously reduced
Terrestrial Hibernation Body temperatures are determined by hibernation site Eastern Massasaugas hibernating in crayfish burrows Hibernate below 60cm Maintain a stable temperature Hibernate underwater May conserve heat Temperature C Snake Temps Date Surface 30 cm 60 cm
Aquatic Hibernation Rest on the bottom of ponds Use extrapulmonary respiration Amphibians Normoxic water demands met Reptiles Some cutaneous respiration Aerobic in normoxic water Anaerobic in anoxic or hypoxic water Just as long as there is not a complete freeze
Speaking of Completely Freezing Most herps in the temperate regions can briefly supercool Some species produce cryoprotectant proteins Wood Frog Can tolerate upward of 35 45% of total body mass as ice All life processes stop Suspended animation Cryoprotectants are glucose Gradual freezing allows production of protectants This ability extends to the cold late winter early spring breeding season Wood Frog (Rana sylvatica) Frozen
Freeze Tolerance in hatchling Turtles At northern latitudes many turtles over-winter in the nest Turtles were cooled to -2.5 C and held there for 24 hours Ornate Box Turtles 2/5 hatchlings survived 4/4 adults survived Can tolerate short periods of freezing Painted Turtles 6/6 hatchlings survived -2.5 C Supercooled can survive - 3.0 C for ~30hrs Ornate Box Turtle (Terrepene ornata)
Aestivation Western Spadefoot Toad (Spea hammondii) Desert and semi-desert habitats Periods of drought Water conservation mode Many desert amphibians, some turtles, lizards and snakes Retreat to deep burrows in moist soils The Western Spadefoot Toad Deserts of the south west Spends more than 90% of its time in dormancy Only active with the first heavy summer rains Explosively breed, feed for 2 3 weeks then back in
Physiological Ecology Water and Salt Balance Respiratory Gas Exchange Respiration and Metabolism Thermoregulation Dormancy Energetics
To be continued