herps exam 2

Ectothermy

“outside heat”, reliance on solar radiation, ancestral condition

Endothermy

“within heat” regulates temp with metabolized food, minor use of direct sunlight

Body temp importance

Biochemical reactions allow organisms to function, can also affect rate of travel of nerve impulses

Q₁₀ Effects

Rate of a biological process changes with a 10-degree change in temperature. 2 means the rate doubles, a 3 triples etc. A 1 is temperature independent 

Higher efficiency

Ectotherms are far more efficient in energy conversion, 50% in ectos to 2% endos

Low metabolic demands

Allows for more niches to be filled, can survive in multiple environments

Ectothermic productivity 

extremely prolific, capable of producing relatively large numbers of biomass

Estimated number of redbacked salamanders

15 to 242 billion

implications of body size

Most herps are small when compared to birds/mammals, which leads to optimal surface area due to less heat loss

metabolic rate

resting rate is a function of body size, smaller body = slower metabolism 

Ecological niches due to size

Can fill habitat patches in bedrock, streambeds. small shelters like cracks in bark and rotting logs, eat smaller food items like mites, springtails, etc. 

Downsides to ectothermy

Limits activity window and leads to periods of inactivity

Torpor

period of inactivity due to low food / poor conditions. Out of sight and nearly inactive for months to years

Brumation

“hibernation in ectothermic animals”. Seek thermal refuge to avoid freezing. Reduced activity and glycogen stores for energy.

Estivation

Dormancy during hot and dry conditions, seek refuge to avoid overheating, a similar physiological response as hibernation

Vulnerability to climate shifts

dependence on heat sources make them susceptible to changing climate

Amphibian specific challenges

permeable skin, little behavioral control, constant evaporative heat loss, cannot exploit warmer terrestrial habitats

Reptile skin and thermoregulation

Highly impermeable skin permits direct sun exposure, scales, and temperature control via behavior is more common in reptiles 

Activity temperature range

temperature range over which an individual is active

Optimal temperature 

temperature at which performance of some biochemical reaction or behavior is maximized

Critical thermal maxima / minima

higher and lower temperatures at which locomotion is impaired

Absorbing solar radiation

Qabs = S * A * vfs, equation for radiation absorption

Qabs = S * A * vfs

= intensity of radiation

Qabs = S * A * vfs

= surface area of the animal

Qabs = S * A * vfs

= proportion of the animal’s surface that is exposed to the radiation

Qabs = S * A * vfs

absorptivity, proportion of the energy that is absorbed rather then reflected 

Basking

Heliothermy, extensive in reptiles and some amphibians, involves relocations and postural adjustment 

Amphibian basking

sun patches critical, oviposition location, varies by life stage

oviposition

the act / process of laying eggs

Albedo

Changing color to change absorptivity, disperses melanin to absorb light

Conduction 

Thigmothermy, exchanges from solid to solid, managed mainly through posture shifts that change the degree of body contact with substrate 

Kleptothermy 

harvesting heat via conduction from endotherms

convection

Heat exchange between a solid and movement of the medium (air or water). Involves differing amount of contact with fluid flows

Evaporative cooling

Water passed across skin, vaporizes on surface. Conversion of water from liquid to gaseous phase involves a loss of heat

Evaporative cooling and amphibians

it sucks, permeable skin leads to water loss, limits thermal regulation, only few species have evaporative heat loss control

producing Metabolic heat

Female pythons use muscle contractions to produce heat. Metabolic rate is 20x that of non brooding

Metabolic heat

Generated through muscular activity, retained in thick oily skin

Dormancy

A response to extreme colds and hots. Seek thermally stable areas such as caves or wetlands. Respire dermally

Brumation on land

Must stay below the frost line, will slowly dig deeper to avoid it. Vertical migration 

Migration

Overwintering sites, species move to warmer areas

What if you cant dig?

Freezing is usually lethal, water freezes first and will block respiration, causes death upon waking

Cryoprotectants

High concentrations of sugar alcohols inside cells to prevent freezing and equalizes osmolar differential when ice forms in cells

Water balance

Any water in MUST equal water out 

Water relations

Amphibs and reps are aqueous systems, water is vital

Osmoregulation 

The active process of regulating the fluids in ones body 

Dermal loss

Loosing water through skin, frogs loose water at the same rate of an uncovered bowl of water

reptile water loss

Most resistant skin in all vertebrates, evaporate 20-30 times less

Water uptake

liquid water + pre-formed water + metabolic water

water loss

evaporation + urine + feces + salt glands

Amphibian water intake

“cutaneous drinking”. Dermal absorption primarily through “drink patch”

drink patch

Thin, heavily vascularized patch of skin

Salamander water intake

Coastal grooves catch water onto animal through capillary action “wicking”

Reptile water intake

Primarily drink through mouth, some species harvest water through rain/fog or through running the water along skin 

Pre-formed water intake

Water gained through tissue eaten as food, may be the only source or reptiles in the desert

Metabolic water intake

Metabolizes fats and proteins into water, a great source during droughts and for eggs

Evaporation water loss

Regulated through behavior, reduce exposure of moist surfaces. Closing eyes, tucking limbs, curling body

Aestivation

Dormancy and a “cocoon” of dead skin. Can reduce the water loss of a frog by 95%

Aggregation 

Some reptiles will cluster together in large groups to minimize evaporation 

Water loss through feces and urination

Nitrogenous waste from metabolism, excretion requires water

Ammonia (NH3) in waste

Amphibians only, inexpensive but highly toxic, .5 L for 1 g of nitrogen removed

Urea (CH4ON2) in waste

Turtles mostly, some amphibs. highly soluble in water, 0.05 L of water for 1 g of nitrogen. Energetically expensive to produce, non toxic and can be accumulated without damage

Manipulating osmolar gradients 

Western spadefoots. Underground 9 months of the year, the bladder is full of dilute urine. For the first 7 months, plasma and urine concentrations do not change

Uric acid (C5H4O3N4) in waste

Snakes and Lizards. Very insoluble in water, next to no water loss, ~0.001 L per 1 G of nitrogen. Non-toxic and easily stored. Energetically very expensive to produce 

Water loss via salt glands

Very expensive energetically, expelled externally, max concentration of urine 

Lizard salt glands

Modified nasal glands, hence the “spitting” of excess salt

Turtle salt glands

Orbital glands, hence the tearing

Crocodiles / sea snakes

Lingual salt glands from modified salivary glands

Lingual glands

Crocodilians, exuded on tongue. spits salt out

Metabolic rates in amphibians and reptiles 

Basal rate is low, O2 consumption rates are 10-20% of what endothermic vertebrates do. leads to less energy overall

Lower energy requirements allow…

Dependence on temporally clumped resources, egg eating lizard and snakes can go months without food. Desert geckos can store 9 months worth of food with libitum feeding

Less oxygen required

Animals can survive longer in anoxic environments

Oxidative metabolism

break down of food into cellular energy, aerobic pathway, oxygen and glucose transported throughout the body

Aerobiosis

VERY efficient production of ATP per unit of glycogen, slow response time and requires oxygen

Gas exchange

All amphibians and some reptiles can use both air and water as respiratory medium. Requires a moist membrane 

Gas exchange and metabolism

Critical via aerobic pathways. Gases flow from high to low concentration passively across cell membranes. Requires a specialized and moist membrane 

Sites of gas exchange

Can take place in the lungs ( All reptiles) (many (NOT ALL) amphibians). Or the surface of the skin, gills, pharynx and cloaca

Pulmonary gas exchange

Gas exchange which takes place in the lungs

Non-pulmonary gas exchange

Gas exchange which takes place on the surface of skin, gills, pharynx and cloaca 

Negative-pressure ventilation 

Involves increasing volume of thoracic cavity to create negative pressure 

Positive-pressure ventilation

Buccal pumping. Seen in amphibians with lungs. Present in reptiles that can inflate lungs as defense

Snake pulmonary respiration

No diaphragm, narrow rib cage to push air out and then widening it again. After each breathing cycle, apnea (few seconds to a few minutes). Mostly via the elongated right lung

Structure and ventilation of snake right lung

Anterior vascular lung that does gas exchange, posterior saccular lung that dosen’t (acts as a reservoir and can also aid in buoyancy) 

Lunglessness 

Plethodontid salamanders have highly reduced lungs. Act as an impediment in fast moving, cold streams. Nearly 100% of O2 and CO2 exchange is cutaneous 

Gills

Strictly for aquatic respiration, long thin filaments and heavily vascularized supported by viscous medium of water

Skin adaptations

Vascular folds with abundant skin capillaries near surface

Swaying behavior in aquatic species

O2 content of water decreases with rising temperatures, running water carries CO2 away 

Skin appendages

appear during the mating season on males when oxygen demands are high due to courtship or paternal care activities 

Cutaneous respiration in reptiles

Can be high (up to 30%), via scale hinge-interscaler spaces, especially lizards and snakes and aquatic turtles

Buccopharynx

Generally a minor surface for normal respiration, vital for long-term submergence in some species. In some turtles sufficient for survival during long-term submergence such as brumation 

Cloaca

Several turtles have bursae in cloaca, rarely surface for air, but constantly pump water in and out of cloaca at 1-5 s intervals

Other metabolic pathways

Despite their low basal metabolic rates, herps still need to “behave” like endotherms on occasion. Aerobic respiration insufficient

Extreme increase in metabolism

pythons eat 1/4th body weight, metabolic rate up to 1,000 percent, for weeks. 

Anaerobic respiration: glycolysis

Converts cellular glycogen into lactic acid and ATP without need for oxygen. Highly inefficient. But depletes cellular glycogen reserves

Costs of anaerobiosis

animal is quickly depleted, recovery via breakdown or conversion of lactic acid can last hours or even days

Limbed locomotion 

has not changed much since Devonian period, limbs stout and sprawling. Rise up to move 

Crocodilian locomotion

Characteristic “high walking” combined with ankle twisting

Turtle locomotion 

Locomotor problems from inflexibility, ribs attached to shell, simply raise themselves vertically off the ground. Support them selves from three points (tripod) 

Lizard locomotion

accelerate rapidly and change direction, unusual hind foot morphology (4 bones joined tightly together, 5th is used as lever for foot) 

Bipedal locomotion over water

Most support from stroking foot downward while expanding air cavity underwater. Minimizes downward forces by pulling foot upward before the cavity collapses 

Anuran locomotion 

Long hindlimbs: jumpers or swimmers. Short hindlimbs: Walk, run, or hop. Short hind and forelimbs: walker / burrowers. Long forelimbs: Climbers