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Study of amphibians & non-avian reptiles **both groups were included within a single discipline for a long time because they were not known to be distantly related to one another.


How many living species of Amphibia are there?

~7080 living species


What are the 3 major extant clades included in Amphibia?

Anura (Salientia = stem based name) Caudata (Urodela = stem based name) Gymnophonia (Apoda = stem based name)


How many species are within the Anura clade?

Frogs & toads ~6250 species


How many species of Caudata are there?

Salamanders & Newts ~640 species


How many species of Gymnophiona are there?

Caecilians ~200 species


How many living species are in Reptilia?

~19,500 living species


What are the 5 major extant clades within Reptilia?

Chelonia Crocodylia Rhynchocephalia Squamata Aves (10,000 species) ~9500 sp. are non-avian


How many species of Chelonia are there?

Turtles ~ 320


How many species of Crocodylia are there?

Alligators, crocodiles, & caimans ~25 species


How many species of Rhynchocephalia are there?

Tautara ~2 species


How many species of Sqamata are there?

Lizards & Snakes ~ 9200 species


How are phylogenetic relationships inferred? What types of things are not used?

-infer phylogenetic relationships based on derived characters, or apomorphies -do not base relationships on plesiomorphies (ancestral or primitive characters)


What types of data can be used to determine phylogenetic relationships among taxa?

Morphology (osteology, external morphology, etc) , DNA sequences, others such as behavior, allozyme data, karyology, etc.


What methods can be used to determine phylogenetic relationships?

Cladistic analysis (parsimony; used for frequent method for morphology & non-DNA data), and Maximum likelihood & Bayesialn methods (used primarily DNA data and is a model-based analysis)


What is a monophyletic group? A paraphyletic group?

Monophyletic group- a common ancestor plus all of its decedents Paraphyletic group- a common ancestor plus some, but not all, of its decendents


What is a synapomorphy? A synplesiomorphy?

synapomorphy- a shared derived character, derived character exhibited by the common ancestor of a clade synplesiomorphy-a shared ancestral character **don't use these to infer relationships**


Compare and contrast node-based names vs. stem based names.

Node based name is the most recent common ancestor of two or more groups and all of it's descendants. Stem based names include all taxa more closely related to a particular group than to some alternative group. Similarities: Both are used to describe parts of a phylogeny and to communicate effectively with others about a specific phylogeny. Differences: They are used to describe different parts of a phylogeny. Stem based names are a more inclusive group and node-based names are used to describe the common ancestor of a particular group and all descendants.


Compare and contrast positive-pressure lung ventilation vs. negative-pressure lung ventilation.

Positive-pressure ventilation is applying pressure to move air into the lungs. Negative-pressure ventilation is expanding a space to create a vacuum to draw air into the lungs. Similarities: Both are methods of ventilating the lungs. Differences: One draws air in by creating a vacuum (negative-pressure) and the other physically pushes air into the lungs by applying a pressure to a sac (positive-pressure)


When naming node-based taxa, why do systematists generally use the more commonly used (traditional) name?

Commonly used names are restricted to node-based taxa because there is higher confidence in the construction of these groups. The reason for this is that often soft anatomy parts are used to identify extant taxa, and these parts do not fossilize well, so there is a little more uncertainty with groups that include only fossilized forms or extinct taxa. For this reason, when naming a node-based name, the more commonly used name is used to communicate certainty.


Describe the evidence that suggests that Ichthyostega was better adapted for terrestrial life than earlier forms of the early extinct osteolepids (ex Acanthostega)?

Earlier forms such as the Acanthostega possessed internal gills, relatively long limbs which would have been weak support for the body on land, had a pelvic girdle weakly attached to a poorly developed vertebral column, short thin ribs that would not have been able to protect the vital organs, and tail fin well suited for swimming but would have been mangled on land. The Ichthyostega had robust forelimbs with weight-bearing elbows (but weak hind limbs), a vertebral column with supporting zygapophyses, smaller supraneural arches on tail meaning less support for the tail fin, a massive rib cage that would have protected vital organs well on land, no evidence of internal gills. **The gills, larger forelimbs and ribs, and support for vertebral column, along with bending wrists and neck are all good evidence. 


Why might some herbivorous reptiles (particularly those living in deserts) modify their consumption of plant material over a given season?

Sometimes in a hot desert eating plants may be the only way for a reptile to get any water. Of the few ways reptiles are able to obtain water for their survival, drinking or metabolic water intake may not be enough, so they may have to use the only other option, preformed water by food intake. If they are able to obtain more water from their environment by drinking it, they may not have to depend on their food, and may eat less.

Some desert reptiles may also stop feeding if the water content of a plant falls below a certain level because it costs more energy and water to digest the plant than what would actually be obtained from eating it. Chuckwallas (Sauromalus) is an example of this. 


What is the biological reason that amphibians are generally thermoconformers?

The main reason amphibians are thermoconfomers is because of their permeable skin and evaporative cooling. The amphibians are unable to absorb heat from their environments by sitting in the sun like reptiles because they will lose more of their water through evaporation, and as this happens evaporative cooling will cool the overall body temperature.


Describe the mechanism used by crocodiles to ventilate their lungs.

The liver is involved with compressing and expanding the lungs in the crocodiles. The liver act as a plunger and is located behind the lungs. For exhalation, the muscles pull the liver forward to compress the lungs and push the air out (positive pressure). For inhalation the muscles pull the liver back, expanding the area of the lungs as this occurs, and causes a vacuum to suck air into the lungs (negative pressure).


For a terrestrial amphibian, what is the advantage of excreting urea instead of ammonia as a means of getting rid of nitrogenous waste products?

Ammonia is very toxic and cannot be stored in the body. It is also very water soluble, making it convenient for fish to eliminate it easily across the skin or gills. Terrestrial amphibians cannot excrete ammonia out of their skin because it is toxic. Urea is energetically expensive to convert from ammonia, but it is nontoxic and can be stored in the body in high concentrations. While stored in the body, it can also be used to raise the osmolalitiy of body fluids to help with water retention.


Given the following groups, draw a phylogenetic tree/cladogram that shows the evolutionary relationships among taxa/groups: Amphibia, Aves, Caudata, Dipnoi, Ichthyostega, Mammalia, Squamata, Tiktaalik

Aves & Squamata closely related (both Reptilia), then Mammalia; Anura, Caudata, & Gymnophonia make up Amphibia.  Closest relatives to Amphibia are Ickthyostega, Acanthostega, and Tiktaalik, in order from closest to least related. Amphibia with Reptilia and Mammalia make up Tetrapoda. Sister taxa to Tetrapoda is Dipnoi (lungfish). 

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List and explain the methods of water gains and losses for Amphibians and Reptiles.

Balancing water gain and loss is required to maintain relatively constant amounts of water in the body.

** Ions follow similar routes**

Gains include: liquid water + preformed water + metabolic water

Liquid water includes any water that enters through the mouth (retiles drink) or through the skin or pelvic patch (amphibians do not drink), Preformed water is any water in the diet, and metabolic water is formed by cellular metabolism. Metabolic water may be enough to get some species by for a while if they decrease their activity so the water is sufficient. 

Losses include: evaporation + urine + feces + salt glands

Evaporation is water turning to gas and leaving the body, and is major for terrestrial amphibians because it can cause cooling of the body by evaporative cooling. Urine and feces are fluids that contain nitrogenous waste and ions, and some water is lost with waste. Some water is also lost through the salt glands, although salt glands are generally there to help absorb needed ions back into the body and getting rid of the ions that are not needed while decreasing the amount of water that would be used if the kidneys were to get rid of the salt.  



During the evolution towards a terrestrial existence, numerous changes had to occur. For more aquatic ancestors, describe what changes had to be made in the following systems for living on land: 

Respiratory system

urogenital system

and the feeding system

Make sure you explain why these changes had to occur.

Respiratory system: In the water gills can be used to breath, but gills are not supported and will collapse in on themselves when on  land. Lungs were already present in fish long before invasion of the terrestrial environment, but was primiarily used to control buoyancy with a secondary role of respiration. On land the lungs are the primary mechanism of gas exchange for the body as well as the skin with amphibians (the loss of dermal scales aids cutaneous respiration). 

Urogenital system: In the water, Ammonia can be elliminated easliy at any time because it is water soluble. Ammonia can not be stored in the body because of it's toxicity, and is released from the gills and body any time needed. On land, the renal system, or kidneys, is the primary mechanism for eliminating nitrogenous waste via urea and uric acid because these are non-toxic and can be stored in the body for long periods of time. 

The primary feeding system in water for fish is suction feeding to capture prey. Some suction feeding is exhibited in some aquatic amphibians and reptiles, but on land grasping jaws and/ or a tongue protusion are needed to capture prey. 


During the evolution towards a terrestrial existence, numerous changes had to occur. For more aquatic ancestors, describe what changes had to be made in the following systems for living on land:

Musculoskeletal system

Sensory system

Make sure you explain why these changes had to occur.

Muscoskeletal system had to change because on land the body can't be supported by the boyant aquatic medium. Locomotion is a major factor in why this system had to change as well. Changes made to the muscoskeletal system were: hands and feet required, because fins are not very useful on land. The limbs and associated musculature must be more robust to compensate for gravity, because there is no longer a bouyancy provided by water. The vertebral column must be strong enough to support the body weight, so the pelvic girdle was fused to the vertebral column via the sacrum. Also, the rigid connection between the skull and vertebral column was freed to allow more movement of the head. 

Sensory system modifications were neccessary for both vision and hearing. Hearing in an air medium required a modification of the stapes and the evolution of a middle ear from the lateral line system. 


What were the two first vertebrates with digits?

Explain the morphology of each. 

Acanthostega and Ichthyostega. Both are common in the fossil record in the late Devonian Period (~370-365 mya) and had "panderichthyid"-like tail, fin rays, and caudal fins. Both had a polydactyl condition, or many digits. 

The Acanthostega had 7-8 well developed fingers and toes, relatively long limbs that would have been weak support for the body weight, the pelvic girdle was also weakly attached to the poorly developed vertebral column, and short, thin ribs incapable of protecting vital organs. It also had a tail fin well-suited for swimming. It also possessed internal gills (known because fossils possess a groove on ceratobranchials that accommodates artery in gilled fishes and a flange on anterier margin of the shoulder girdle that supports posterior wall of operculum chamber in fish), fish-like stapes (retained the lateral line system), and was likely completely aquatic. 

The Ichthyostega had forelimbs that were more robust than the Acanthostega and weak hindlimbs. It also had a vertebral column with supporting zygapophyses, smaller supraneura arches on the tail that provided less support for a tail fin, had a massive rib cage, no evidence of internal gills, and was probably primarily aquatic but may have hauled itself onto land. 



What has been the most recent fossil discovery in the Osteolepida group?

Where did it fit into the current phylogeny?

Where was it found, and how old is it believed to be?

The Tiktaalik was published about in 2006 by Daeschler, et al.

The fossil was a tetrapod-like "fish" 

It was discovered in Greenland and is estimated to be ~ 375 million years old

The Tiktaalik is a basal lineage of the Osteolipids (the stem based name of Tetrapoda)


How many Devonian basal Osteolepids have been found?

Where have the fossils mostly been found?

How long after this did other fossils begin to appear in the fossil record?

What were these other fossils?


There are now ~ 17 Devonian basal osteolepids (atleast 12 genera described) and most have been from Euramerica

Within the next 30-40 million years, two main lineages appear, the Temnospondyli (Amphibia) and Anthracosauria (Amniota)


List 3 reasons why water balance for animals is very important. 

1. Biochemical reactions depend on proper concentrations of cellular substrates and salts

2. Spatial relationships of intracellular organelles partially depend on cellular water volumes

3. Blood carries chemical substrates, products of chemical reactions, and other biologically important compounds. 

For animals, ~70-80 % of body mass is water. Water and dissolved solutes must be kept in proper balance for survival


List two reasons why the maintenance of proper body temperature is important.


1. Biochemical reactions are affected by temperature ( reaction rates increase as temperature increases and decrease as temperature decreases).

2. Temperature affects cellular environments (Decreased viscosity of cytoplasm, increased permeability of lipid membranes, and increased speed of speed/force of muscle contractions)



What is Osmoregulation?

What are some challenges associated with this? 

What potential structures or organs are involved with this?

Osmoregulation is the control of water and salt (ion) balance in the body

Challenges associated with this are dealing with water gain and loss or ion gain and loss

Potential organs or structures involved are the skink, the gills, digestive tract, or kidneys and bladder. 


Explain the osmotic challenges faced for animals living in the ocean. 

For those living on land. 

For those living in fresh water. 

In salwater the animal is hyposomotic compared to its environment, and because its internal ion concentration is less than tha in the surrounding environment, water moves outward. 

On land, the animal is a container of water and ions, but because the animal is not in an aqueous environment, internal fluctuations in ionic balance result from water loss to the relatively drier environment. The animal actually has much higher ion concentration than surrounding air, and if ionic concentrations reach high levels, as they do in some desert reptiles, ion transfer can occur via salt glands, usually in the nasal or lacrimal region.

In freshwater, the animal is hyperosmotic to its environment, and the greater internal ion concentration causes water to move inward. 


On land and in freshwater ion concentrations are internal > external, and in saltwater external ion concentrations > internal.



What happens to the osmotic concentration of urine as it passes through the kidneys and bladder in amphibians and reptiles?

Which would have a lower overall osmotic concentration?


The osmotic concentration of urine would decrease as it travels through the kidneys and bladder. 

The overall osmotic concentration of urine would be lower for reptiles because reptiles produce relatively concentrated urine which minimizes water loss. 


What feature allows terrestrial anurans to get the water from their environment they need?

How is this feature used in combination with osmolality of body fluids used in desert anurans?


A pelvic patch which is an area of thin skin underlain by a capillary network in the pelvic area that allows them to absorb water from the soil. 

In desert anurans, the increase in osmolality of body fluids by the accumulation of urea in the body, allows them to still get water from the soil as the soil dries out. It increases their efficiency of water absorption from the soil by making their internal ion concentrations higher than the external concentrations, causing water to flow into the body through the pelvic patch. 


How are water and ion concentrations inside the bodies of freshwater amphibians kept constant?

The osmolality of body fluids for freshwater amphibians is greater than that of the surrounding medium and because of their highly permeable skin there is an influx of water and a loss of ions outward. 

The influx of water is balanced by the kidneys generating large amounts of dilute urine.

The outward flow of ions in balanced by active transport of ions back across the skin to replenish the lost ions in the body. 


How many salamanders and anurans are known to inhabit salt water environments?

How do amphibians living in salt water deal with balancing their internal ion and water concentrations?


There are ~12 salamanders and ~60 anurans that inhabit or tolerate brackish environments. 

Because of the high ionic concentrations of the surrounding environments, they have to deal with constant water leaving the body and ions entering the body. This is controlled by the accumulation and retention of organic and inorganic solutes into the body. This raises the internal osmolality of the body fluids, making them greater than the surrounding environments. The water moving into and out of the body is atleast balanced, and there may even be a net influx due to this. 


Do reptiles face some of the same challenges with living in saltwater or freshwater aquatic environments as amphibians do? Why or why not?


No. Water movement across retilian skin is minor because they posess lipids in their skin that make it relatively impermeable. There may be a minor influx of water and loss of ions in freshwater environments or a minor loss of water in marine reptiles, but not enough to harm the animals. 

Amphibians have very permeable skin and have to find ways to deal with water loss in saltwater conditions (increase internal ion concentrations, or increase osmolality of internal fluids), and deal with water gain in freshwater conditions (dilution of urine to rid excess water) 


Amphibians use their permeable skin for cutaneous water collection. Do any reptiles have the ability to obtain water by cutaneous water collection? 

Yes, but not because of permeable skin. Some reptiles (Moloc horridus & Phymosoma cornutum) have channels on their dorsum that channels rain water into the corners of their mouths. 


How do some amphibians deal with cutaneous water loss through evaporation?

Most terrestrial and aquatic amphibians have low resistance to evaporations, but there are two exceptions:

1. Some arboreal hylids, rhacophorids, and hyperoliids increase the number of chromatophores in their skin by employing lipids and/or waxy esters to increase their resistance to evaporation. They can also lower evaporation rates by changing where they are within their environment, like moving out of the wind or into the wind, etc. 

2. Some Australian hylids and myobatrachids and salamanders can form cocoons to increase their resistance to evaporation. The cocoon formed is just shed layers of the stratum corneum, and resistance to evaporation is comparable to some of the arboreal anurans. 


What is the difference between ammonia, urea, and uric acid in terms of water solubility, toxicity, and energetics.

Ammonia is water soluble, toxic so cannot be stored in the body, and cost nothing for the body to produce as a waste product. 

Urea is also water soluble, non-toxic so can be stored in the body, but costs energy to turn ammonia into urea for waste. 

Uric acid is not water soluble, non-toxic so can be stored in the body, and energetically expensive to convert ammonia to uric acid. 




For most terrestrial vertebrates, how is salt excretion handled?

How do many reptiles handle getting rid of extra salt in the body?


For most terrestrial vertebrates salt excretion is a renal function. 

Many reptiles have organs called salt glands, which are an extra-renal pathway for salt excretion. Salt glands allow for secretions of salt in high concentrations while saving water. If the kidneys or urine were used to get rid of this salt, it would require much more water than what most reptiles have, so salt glands require energy, but save water. 


Where are different places salt glands can be located on animals?

What is the reason for many locations?

Why have these animals evolved salt glands?

Salt glands are located in different areas; tear ducts, nasal area, near mouth, near renal area.

Salt glands have evoloved independently in different lineages of reptiles, and are all non-renal pathways for salt excretion.

All have evoloved salt glands because they have to deal with the high levels of salt coming into the body because of their external environments, whether in brackish water, or marine or desert environments.


Why has the study of thermal biology of amphibians and reptiles received a great deal of attention?


1. They are ectotherms and most of their thermal energy is received from external sources

2. They have optimum body temperatures that vary greatly among the groups

3. There are various behaviors/strategies used to maintain optimum body temperatures for at least some time period for these animals. 


List the different ways heat can be gained or lost from amphibians and reptiles.

heat gain and loss = Q +/- M+/- R+/- C+/- LE+/- G

Q= solar radiation aborbed by animal

M=metabolic heat production

R= infrared radiation received or emitted by animal

C= Heat gained/lost by convection

LE= Heat gained by condensation or lost by evaporation

G= heat gained/lost by conduction


What are the different routes of heat gain and loss for aquatic amphibians?


  • convective and conductive heat to and from water
  • gaseous exchage into and out of water
  • behavior response to and from warm water
  • direct sunlight
  • air breathing

**FIgure 7.4 in book**


What are different routes of heat gain and loss for secretive or nocturnal amphibians?


  • Thermal radiation from environment into amphibian
  • convective heat gain and loss 
  • gaseous exchange
  • heat coduction to or from ground
  • evaporative heat loss 


What are some of the different routes of heat gain and loss in diurnal and basking amphibians?


  • Heat conduction to and from ground
  • Evaporative heat loss
  • Thermal radiation to environment
  • Gaseous exchange
  • Direct sunlight, and scattered and reflected light cause convective heat gain
  • Convective heat loss
  • Thermal radiation from atmosphere for gain
  • water loss causing heat loss
  • water input from soil


Why does the heat gain and loss of a reptile differ greatly from that of an amphibian?

Because water loss is much lower in retiles and influenced body temperature much less. **this also limits the reptile in its ability to absorb water from the environment, so a trade off. 


(Q) Solar Radiation

  • Solar energy directly or indirectly absorbed by the animal
  • wavelengths 400-1500 nm
  • rate of absorption depends on intensity of solar radiation, surface area of animal, and the orientation of the animal to sun, as well as absorptivity of the animal (proportion absorbed rather than reflected).


(M) Metabolic Heat Production

  • produced by all animals and amound is largely dependent on activity of animal (homeotherms have higher metabolisms than poikilotherms so their temperatures will be higher) 
  • The efficiency of heat retention depends on body structure and size (larger body sizes are more efficient, as well as those with feathers, hair, fat layers, etc) 
  • Some also have the ability to do coordinated muscular contractions for egg brooding (python) **counts as metabolic heat production


(R) Infrared Radiation


  • Heat radiatied between objects- all object radiate heat
  • Transfer of heat follows gradient from warmer to colder surface
  • Surface texture important in how readily a surface absorbs or radiates infrared radiation


(C) Convective Heat Exchange


  • Heat exchange between animal and surrounding fluid (surrounding medium is air for terrestrial and water for aquatic animals)
  • Temperature differences, animal surface area, fluid velocity, and body size all affect the rate of heat exchage via convection
  • Behaviors such as moving into and out of the wind or climbing can also affect convection


(LE) Evaporative Cooling

What are the steps of evaporative cooling?

What is the limiting factor for the evaporation rate?

How it differs between amphibians and reptiles?

  • Water evaporation cools a given surface

Two steps of evaporative cooling: 1. Water moved across barrier imposed by skin 2. Convection pulls water vapor from outer surface (=actual cooling step).

Limiting factor for evaporation rate is getting water to the outer surface (reptiles have relatively impermeable skin, and some amphibians have thick/evaporation resistant skins and have high resistance to evaporation)

Reptiles experience evaporative cooling by panting in some lizards, and amphibians and their permeable skin cause their body temperatures to be lower than reptiles in similar environments because of this (thermoregulation) 


(G) Conduction

  • Heat transfer between animal and substrate
  • Amount of heat exchange depends on amount of surface contact between animal and substrate
  • Important source of heat at night and early morning
  • In hot deserts, reptiles generally reduce surface contact so they don't get too hot.


How is thermoregulation in reptiles and amphibians generally controlled?

Are reptiles thermoregulators or thermoconformers?

Are amphibians thermoregulators or thermoconformers?

  • a large part of thermoregulation in amphibians and reptiles is behaviorally controlled
  • Reptiles are active thermoregulators 
  • Amphibians are passibe thermoregulators or thermoconformers


What can be said of Active thermoregulators such as reptiles?

  • The precision of thermoregulation can be temporal
  • The body temperature is generally regulated within a narrow, optimum range of temperatures
  • Temperature sensitive region of the brain, the hypothalamus, monitors temperature of blood
  • Heating and cooling rates are generally not equal


What are 3 different ways in which the cardiovascular system helps to regulate body heating and cooling rates?

1. Higher heart rate during heating

2. Intracardiac shunt: blood transfer in heart that increases proportion of blood going to skin and body (decreases the amount going to lungs) 

3. Vasodilation in areas of skin that are warm

**Heart rate can increase to increase blood flow so all blood becomes warmer and decrease when cooling to stop from losing heat to the environment when warm blood reaches surface of skin. Blood picks up more heat when toward the surface of the body, but also loses more heat to evaporative cooling when toward the surface if it's cooler outside. **


Compare and contrast the following:

Homeotherms vs Poikilotherms 

Homeotherms: maintain a constant body temperature and usually have higher metabolisms because of it. A higher metabolism means that they will have more heat produced by metabolic heat production. 

Poikilotherms: have temperatures that vary throughout the day and generally have lower metabolisms because of it. A lower metabolism means they will have less heat produced for the body by metabolic heat production. 

Similarities: both terms used to convey information about animals and their maintenance of body temperatures. 



Compare and contrast the following: 

Heliothermy vs. Thermoconformity

Heliothermic species are active thermoregulators

  • that maintain high, stable body temperatures (primarily lizards).
  •  live in open habitats, with many routes of heat exchange
  • cost of thermoregulation is relatively low 

Thermoconformers are passive thermoregulators

  • That maintain body temperatures close to ambient temperatures (amphibians, many snakes, nocturnal reptiles)
  • live in closed habitats & night, with very few routes of heat exchange
  • thermoregulation comes at a relatively higher cost or may be nearly impossible


Compare and contrast the following: 

Low-cost environments vs High-cost environments

Low-cost environments

  • thermoregulation is complex with many routes of heat exchange
  • open, sunny habitats
  • many behaviors used such as body orientation and exposure to maximize heat uptake and minimize loss
  • Activities limited in time and space, must stay in area to maximize heat exhchange

High-cost environments

  • Thermoregulation is generally less complex with fewer avenues of heat exchange
  • Function at near optimum levels over wider range of body temperatures (thermoconformers)
  • Less constrained in space and time, with active wide-ranging foragers or nocturnal animals







Dormancy= a period of time when an animals environmental conditions exceed the organisms ability to maintain homeostasis so the animal retreats, seeks shelter, and becomes inactive. Regular cycles of dormancy may be a major feature of life. 2 types are Hibernation and Aestivation.

Hibernation= what ectotherms do to avoid winter cold, hunkering down in cold months for long periods of time to avoid freezing. May hibernate deep underground, at the bottom of ponds and/or deep in the mud, in rock outcrops or in hollow trees. Some hibernation sites may be exposed to freezing, and this may require animals to be freeze resistant or tolerant.

 Aestivation= retreat to some deep burrows where there is higher humidity and moisture  to reduce metabolism because there may be extended periods of time where there is no rain and low humidity. This is common in some desert and semidesert anurans. During this time, some may form cocoons to help to decrease water loss. 



Freezing tolerance

Freezing resistance

Freezing tolerance= the toleration or ability to withstand parts of the body freezing for periods of time. Once a certain part of the body begins to freeze, this stimulates the release of glucose/ glycerol from the liver or the formation of glycerol in the body. The accumulation of intracellular glucose or glycerol increases the intracellular osmolality and lowers the freezing point. For freeze tolerant species, up to 50% of the bodies fluids may freeze and respiration, ciruculation, and heartbeat may stop, and for some this may last for weeks. This is only a short term measure though. 

Freezing resistance= the prevention of body fluids from freezing by some stochastic (random) event. This is referred to as supercooling, when ice crystals are absent from the body even though the fluids are at sub-zero temperatures. This in not well known and somewhat a mystery as to why it occurs. Some montane lizards, aquatic turtles, and amphibians. 


What are the two main dangers to amphibians and reptiles when extracellular water starts to freeze?


1. intracellular fluids may also freeze

2. cell dehydration may occur because the osmolality of the extracellular fluid may increase with freezing and cause fluids to be drawn out of cells


Compare and contrast:

pulmonary vs non-pulmonary routes of gas exchange

pulmonary= gas exchange between air and blood occurs across the lung surface inside the body. Lung structures vary depending on organism, and some examples include the different forms of positive and negative pressure respiration. 

non-pulmonary= any other method that is not the lungs for respiration, generally on the external surface of the body. Surfaces that do this are highly permeable to water, as well as oxygen and carbon dioxide. Some amibians have buccal regions, epidermal projections (skin filaments), extensive crest or tail fins, or gills, as well as their skin. Reptiles usually do not exhibit cutaneous gas exchange but some exceptions are sea snakes having gas exchange the length of the body and some freshwater turtles with pharyneal projections or cloacal evaginations to exchange water and gas. 


  • Respiratory surfaces are highly vascularized
  • one or a few cell layers between capillaries and exchange medium
  • Both exchange oxygen and carbon dioxide with body and environment

Differences: different methods of repiration and each is derived from different anatomical systems.


What are some ways that ampibians have increased their rates of cutaneous gas exchange?

What does the rated generally depend on?

Amphibians have increased their rates of cutaneous gas exchange by increasing surface area either with highly vascularized folds, skin filaments (epidermal projections that look like hairs), extensive crest and/or tail fins on the body, or retention of gills in adult stages. 

The rate of cutaneous gas exchange is usually dependent on the rate of movement of the surrounding medium. ie, faster moving water will produce higher rates of cutaneous gas exchange because it brings more oxygen across the skin at any given time. Those with extra surface area to increase cutaneous gas exchange usually live in places where movement of water is not very fast or there are low levels of oxygen in the water. 


What are some examples of different pulmonary gas exchange methods?

Is each method using positive pressure or negative pressure?

1. Buccal pumping primarily exhibited in amphibians. (positive pressure system)

2. Thoracic aspiration in all reptiles. Expansion of thoracic cavity done in different ways. (all negative pressure systems)

Different Thoracic aspiration accomplished by: 

Triphasic respiration in Lepidosaurs (Squamates & Sphenodon)

Liver acting as plunger in Crocodilians

Compression and expansion of lung by movement of the viscera in Chelonians (Turtles)