Lissamphibia Lecture Flashcards
What issue do terrestrial vertebrates face in terms of reproduction?
Desiccation of eggs. Terrestrial vertebrates have evolved methods of internal fertilization and gestation to overcome this.
If a frog is trying to hear a high frequency sound, what will happen in its ear?
The opercularis muscle will contract, causing low frequency vibrations to not be transmitted and only high frequency vibrations will be transmitted to the Papilla basilaris for detection.
If a frog is trying to hear a low frequency sound, what will happen in its ear?
The columellaris muscle will contract, causing high frequency vibrations to not be transmitted and only low frequency vibrations will be transmitted to the Papilla amphibiorum for detection.
What do the Hedonic glands in frogs secrete?
Pheromones
What benefits do mucous secretions in frogs have?
-Evaporative cooling
-Oxygen uptake and CO2 disposal
-Mating
-Prevents desiccation
-Antimicrobial
How can frogs breathe through their skin?
Mixed blood is pumped from the right side of the heart through the cutaneous artery, which takes it to the capillary beds in the dermis where the blood can then pick up oxygen and dispose of CO2. This mechanism is also seen in their buccal cavity.
How is oxygenated and deoxygenated blood kept separate in an Anuran heart?
The shape of the ventricle is able to be manipulated to segregate oxygenated and deoxygenated blood
When do Anurans utilize cutaneous respiration?
When they are underwater. Because of this, they can spend extended periods of time underwater without having to surface
Which hormone is responsible for inducing metamorphosis?
Thyroxine released by the thyroid
What is the hormone called that acts as a negative feedback to delay metamorphosis?
Prolactin released by the pituitary
How do salamanders reproduce?
A male deposits a spermatophore, then uses specific behaviours to rub pheromones secreted by hedonic glands onto the female, causing her to ovulate and pick up the spermatophore. Fertilization is internal.
What characteristics does the ancestral form of an Anuran have?
-More toes (5 instead of 4)
-Specialized and short pelvis
-No urostyle
-Trunk is longer
-Short hindlimbs and toes
What does a long forelimb length indicate?
That the frog is likely more of a walker
What does a long hindlimb length indicate?
That the frog is likely a long-distance jumper
Why do frogs crouch?
The reduce their surface area, thereby reducing water and heat loss
What are some parental care strategies used by frogs?
-Guarded by male
-Make a foam that defends and prevents the eggs from drying out
-Folded into a leaf
-Eggs carried on the frogs back
-Eggs carried in the vocal sacs
What are some reasons that frogs use calls?
-Mating
-Defending territory
-Warnings
What are some costs/risks associated with calling?
-Attracting predators
-Water loss
-Energetically costly
What types of mouths can tadpoles have?
-Superior (surface feeding)
-Terminal (filter)
-Subterminal (bottom feeder)
-Suction (scrapes algae)
-Siphon (passive filter feeding)
Why do Caecilians have skulls with very few holes?
Because of their digging lifestyle. More holes would lead to fractures in the skull
What threats do amphibians face?
-Habitat loss
-Climate change
-Pollution
-Disease (chytridiomycosis)
What body systems must be modified to sustain the transition to land?
Desiccation, musculature, waste excretion, sensory systems, reproduction, respiration, and thermal control
What are the skeletal modifications necessary for the transition to land?
Development of the neck and zygapophyses, development of sacral vertebrae, paired fins into paired limbs, development of an ankle joint, and fin elements into digital elements
What are zygapophyses?
Paired bony projections that extend from the vertebrae in the spine of vertebrates
In the development of the neck, what was lost?
The posttemporal-supracleithrum-postcleithrum articulation
If humans had an posttemporal-supracleithrum-postcleithrum articulation, what would be the equivalent?
Our shoulders would be attached to our ears
Describe the function of the zygapophyses
They serve an important function by interlocking with adjacent vertebrae, providing stability and preventing excessive twisting or bending of the spinal column
True/False? The pectoral girdle and the pelvic girdle have increased association with the surrounding structures in tetrapods
False. The pectoral girdle has decreased association and the pelvic girdle has increased association with the sacral vertebra
Which side of your hand is the postaxial side?
Pinky
Which side of your hand is the preaxial side?
Thumb
As fins developed into limbs, what happened to the axis of symmetry? What is this called?
The axis curved downwards towards the preaxial side. This is called postaxial displacement
What is responsible for the plethora of digits on Acanthostega’s limb?
Hox genes
True/False? All ankles within Tetrapoda have very similar structures
True
True/False? All paired fins are found on either the pectoral or pelvic girdles
True
What are the main modifications of the muscular system during the transition to land?
Decrease of epaxial muscle mass
Subdivision of hypaxial musculature
Where is epaxial muscle located on the body?
Dorsal side
Where is hypaxial muscle located on the body?
Ventral and lateral sides
What do strong zygapophyses limit?
Lateral undulation
What is the main function of hypaxial musculature after subdivision?
Fine-tuning of limb movement
Hypaxial muscles subdivided from ___ to ____ muscles
Two, five
What are the main modifications of the cardiovascular and respiratory systems during the transition to land?
Development of upper trachea
Ribs and mechanical exhalation
Double-circuit circulation
What is the pneumatic duct involved in? What is it homologous to?
It is the duct that leads from the stomach to the gas/swim bladder in physostomous fish. Homologue of the trachea
How do early amphibian tracheas differ from our tracheas?
Lack cartilaginous rings
The ribs in an early tetrapod, Eryops, go from pointed to blunt from front to back. What function does this serve?
This allows for some connective tissue to fill in the gaps, as well as exhalation with the compression of that side of the body
The small ribs of Acanthostega suggests what? What does the flange suggest?
Little protection for the internal organs up on land; internal gills and soft tissue operculum
The robust ribs of Ichthyostega suggests what? What does the robust pectoral girdle suggest?
More internal organ protection from gravity when on land; internal gills
When an amphibian bends to the left, what happens to the air in its lungs?
The left lung gets compressed (positive pressure) by intercostal muscles, while the right lung gets expanded (negative pressure), so air goes from the left lung to the right lung
True/False? Costal ventilation can be used for both inhalation and exhalation
False. Only for exhalation
What challenge do single-circuit organisms face when out of the water?
The pooling of blood due to low blood pressure and lack of support for gravity
Describe a double-circuit circulatory system
The heart has two entrances in which deoxygenated blood is pumped to the lungs and then is pumped to the rest of the body by the other side of the heart
Why is having a double-circuit system more beneficial to have on land?
Having a separate pulmonary system allows for the high blood pressure necessary to fight gravity
What is one of the challenges caused by a double-circuit system? How is this avoided?
High blood pressure may cause issues with the thin blood vessels found in the lungs. This is prevented by having the blood pumped first to the lungs, then to the rest of the system, rather than just all at once, also thinker vessels
What germ layer forms the bladder?
Mesoderm
What are the modifications in the excretory system during the transition to land?
Development of a urinary bladder
Primitive kidney
What advantages does having a urinary bladder give terrestrial species?
Concentration of ammonia so less frequent urination. This also prevents pheromones and other smells from being released all the time, which would make it easier for predators to find these species
True/False? Primitive amphibians had fully developed kidneys
False. Their “kidneys” ran throughout their entire body system
What is an advantage of having kidneys?
Allows for the high concentration of solutes in one particular area of the body instead of a low concentration throughout the body. This allows for greater water reabsorption
Which sensory systems are affected by the transition to land? Why?
Vision, hearing, and olfaction. Change in density of the medium they occupy (dense to light)
In which ways to the fish and amphibian eyes differ?
Fish: ciliary muscles move the lens in any direction, lens is spherical
Amphibians: ciliary muscles change the shape of the lens by stretching it, lens is oval
Air has a lower refractive index than water. Why is this important to consider in relation to the eyes of fish vs. amphibians?
The lenses of fish do not have to change shape in order to focus light in a certain area as the refractive index for the lens is the same as the water, so the light doesn’t get refracted. On the other hand, amphibians have to change the shape of their lenses to accommodate for the difference in refractive indexes
The hyomandibula is a homologue of what structure?
Stapes (ossicle) and ventromedial portion of Columella
Describe the path sound waves take in water for teleosts
Sound travels through the body of the fish into the swim bladder, where it gets redirected to the inner ear by Weberian ossicles
Describe the path sound waves take on land for teleosts. Why does this occur?
Sound will reflect off the body of the fish as air and the body of the fish are different densities
True/False? The hyomandibula is considered a “floating bone”, as it doesn’t articulate with other surrounding bones
True
What are the two modifications to olfaction due to the transition to land?
Increased subdivision of the olfactory system
Increased surface area associated with inhalation
How is the surface area increased for the olfactory system in land-dwelling animals?
Extended rostrum and increased turbinates
Which senses are worse on land? Which are better?
Worse: sight and hearing
Better: olfaction
What are the reproductive system pressures associated with the transition to land?
Aquatic necessity, as their eggs cannot survive without desiccation
What evidence suggests that early amphibians depended on water? What is this called?
Larval stages exhibited bones that support external gills (ceratobrachials, hyobranchials). Adults also exhibited a lateral line system on their heads. Obligate aquatic living
How do we know all these transitions happened?
Most evidence comes from the fossil record, developmental, evolutionary, and phylogenetic studies also filled some gaps, as well as studying modern species
What is the difference between lissamphibia and amphibians?
Lissamphibia are only extant (living) species, Amphibians are extant and extinct
What are the synapomorphies of lissamphibians?
Green rods
Pedicellate teeth
Moise skin with mucous glands (cutaneous system)
Levator bulbi
Unique ear apparatus (papilla amphibiorum, papilla basilaris)
What purpose do green rods serve in lissamphibia?
Allow for greater colour perception (blues and yellows)
What are pedicellate teeth?
They are teeth tipped with exposed dentine, which can break off if prey struggles, instead of tearing the whole tooth out or breaking the jaw. Cannot regrow, but they do replace themselves like shark teeth
Where are mucous glands located? What is their function?
Located near the epithelium to ensure moistness of the skin. Allows for the absorption of oxygen through the skin
What is the levator bulbi muscle?
When it contracts, it brings the eye inwards towards the mouth. This allows for more pressure for buccal pumping and acts as an aid for swallowing
Which auditory pathway is used for sounds with a frequency of >1000Hz?
Papilla basilaris
Explain the pathway for sounds >1000Hz
Sound enters tympanum, travels through the Columella, then to the papilla basilaris
Papilla basilaris pathway: Which muscles are relaxed/contracted? Which bones can/cannot vibrate?
Relaxed: Columellaris
Can vibrate: Columella
Contracted: Opercularis
Cannot vibrate: Operculum
Which auditory pathway is used for sounds with a frequency of <1000Hz?
Papilla amphibiorum
Explain the pathway for sounds <1000Hz
Sound enters opercularis, travels through the operculum, then to the papilla amphibiorum. Sound may also enter right through the operculum
Papilla amphibiorum pathway: Which muscles are relaxed/contracted? Which bones can/cannot vibrate?
Relaxed: Opercularis
Can vibrate: Operculum
Contracted: Columellaris
Cannot vibrate: Columella
Why do amphibians have such a complex ear?
Allows for the distinction between different sounds. For example, mating calls may be at a higher frequency than 1000Hz, so they can determine who is available and who is not just by the frequency of the sound they are making
The large holes in the amphibian skull allow for what?
Larger eyes for better vision. Because of these large holes, the eyes can be displaced into the mouth for buccal pumping and swallowing prey
What type of predator are frogs? What features do they have that suggest this strategy?
Ambush predators; catapult-like tongue, sticky saliva, large legs, modified hips, and fused limb bones for better jumping
What is the opercularis derived from? What implications does this have for the audition of caecilians (Gymnophiona)?
It’s derived from pectoral muscles, which caecilians lack. This implies that caecilians have no directional hearing
Why does Gymnophiona lack pectoral muscles?
Because they lack both the pectoral and pelvic girdles completely
What are Gymnophiona apomorphies?
Vermiform bodies with annuli
Highly fused skulls
Lack functional eyes
Sensory tentacles
What are sensory tentacles homologous to?
Nasolacrimal duct
True/False? Gymnophiona is considered to have recently diverged from its MRCA with Batrichia
False. They diverged a very long time ago and became very specialized for their lifestyle
What are annuli?
They are rings that wrap around the caecilian body
What does vermiform mean?
Worm-like
What advantage does having highly fused skulls give Gymnophiona?
Allows for the use of the head like a shovel, able to burrow with its head alone
What is concertina motion? What classes use this for locomotion?
The spine and skin move independently of each other, so the head and spine can be slingshot by the muscles to generate force; Gymnophiona and earthworms
What is the purpose of sensory tentacles?
They are used for sensing chemical signals left by prey
How do caecilians move when they are looking for food?
They bury their snout into the sediment, using their entire head as a nose
What are Anuran apomorphies?
9 presacral vertebrae
Urostyle
Hindlimbs longer than forelimbs
Fused radioulna and tibiofibula
Elongate ankles
Fusion in skull bones
True/False? Anurans are very diverse
True
What are some skeletal characteristics of Anura?
4 digits on the forelimb, 5 on the hindlimb, radius and ulna are fused, tibia and fibula are fused, urostyle replaces the tail and hip vertebrae, elongated pelvic girdle, long hindlimbs and toes
What are the skeletal modifications of Anurans used for?
All for jumping
How does the skeleton of Triadobatrachus differ from modern amphibians?
14 presacral vertebrae, short pelvic girdle, no urostyle, short hindlimbs and toes, small tail with vertebrae
True/False? Anurans have the same skull structure as Temnospondyls
False. Some bones are fused and others are completely lost
Why is it important that Anurans have lost some skull bones and fused others?
Makes room for larger eyes
What are Caudata apomorphies?
Fusion of distal tarsal bones (I and II)
Operculum-dominant auditory system
Quadratojugals absent (skull bones)
Second, third, and fourth ceratobranchials lost during metamorphosis
What is the function of the ceratobranchials?
Supports external gills
Why do Caudates live in temperate environments?
Colder air = higher [O2] = more oxygen intake through skin
What is Basale commune?
The fusion of distal tarsal bones
Caudates lack a tympanum. What does this imply about their hearing?
No papilla basilaris pathway, can only hear low-pitched sounds, shift from airborne to ground-transmitted vibration sensing
The loss of the quadratojugals implies what in Caudates? Why?
Stronger jaw muscles. As muscles contract they get thicker, so more space is needed if more muscles are present
True/False? The skull of Caudates changes with metamorphosis
False. The musculature does, however
How does caudate skull musculature change with metamorphosis?
Strong muscles are not needed in the water, as prey is sucked in using negative pressure in the mouth, so there are less muscles in the head. As they mature and move onto land, strong and fast jaws are needed to catch and hold prey, so they get larger
Why is a stronger heart needed for adult Caudates?
Larvae live in the water and thus use gills for respiration. Gills require a low blood pressure as to not burst them, which is achievable in water, but not on land due to gravity. A stronger heart is needed to pressurize the blood after metamorphosis to fight gravity
What is metamorphosis?
The physical change of the body in order to mature. It is necessary for some species in response to environmental pressures
What is the role of prolactin in metamorphosis? What structure is it connected to?
Suppresses some parts of metamorphosis, like the apoptosis of tail cells; linked to the pineal gland, implies how metamorphosis is linked to environmental stressors
What is the order of structures (and their hormones) used for metamorphosis?
Environmental trigger -> Hypothalamus (TRH) -> Anterior pituitary (TSH) -> Thyroid (T3 and T4) -> Metamorphosis
During metamorphosis, which hormones exponentially increase until climax? Why?
T3 and T4; Positive feedback mechanisms (T3 and T4 stimulate the hypothalamus and anterior pituitary to make more TRH and TSH, respectively)
Describe what happens when prolactin is overexpressed in metamorphosing amphibians
Tails are not reabsorbed (blocks apoptosis)
Describe what happens when T3 and T4 are overexpressed in metamorphosing amphibians
Metamorphosis is triggered
Why are vernal pools necessary for metamorphosis?
Vernal pools dry up and refill seasonally, so when they start to dry up, this triggers metamorphosis in larval amphibians
How does metamorphosis reduce competition between larvae and adults?
The adults become specialized for a separate role that differs from the role the tadpoles fill, which reduces the chances of competition for food, space, mates, etc.
Define “bet-hedging” in terms of metamorphosis
Things that kill off larvae might not kill off adults (extreme drought = adults can survive, tadpoles cannot)
What is paedomorphosis?
Maintaining the larval stage due to no environmental pressures that would otherwise trigger metamorphosis, the deceleration of metamorphosis relative to others
Where is paedomorphosis common?
Permanent lakes and caves
What is peramorphosis?
The acceleration of metamorphosis relative to others
Describe the diversity of paedomorphic species vs. peramorphic species
Paedomorphism allows for a greater diversity in body shapes, while peramorphic species are more restricted
What is polyphenism? Give an example
The precise environmental control over alternate metamorphosis pathways (many different developmental pathways based on environmental pressures); cannibal polyphenism
What is cannibal polyphenism?
Cannibomorphs develop due to overcrowding (environmental pressure). These organisms have much larger heads and teeth than their counterparts, used for consuming the larvae around them
What is the difference between neoteny and paedomorphosis?
Neoteny: Larva matures into an adult (can reproduce), but sustains its aquatic features (external gills, tail, etc). Type of paedomorphism
Paedomorphosis: Larva maintains juvenile form, general term
Is polyphenism a new development?
No, it is ancient in the amphibian lineage
In what ways does climate effect amphibian extinction?
Loss of breeding habitat
Higher temps can interfere with metamorphosis and polyphenisms (limits pathways larvae can take)
Changes in disease vulnerability (Chytridiomycosis)
What is chytridiomycosis? When are amphibians most vulnerable?
A fungal disease that suffocates amphibians by burrowing through the pores in their skin, which destroys their capillary beds; early metamorphosis
Which ceratobranchials are lost in adult Caudates? Why?
2, 3, and 4; no longer needed due to change in respiratory strategy
Is metamorphosis a new development for amphibians?
No, it is recorded in the fossil record for primitive species
During and/or after metamorphosis, what happens to Caudates?
Teeth become pedicellate
Branchials resorbed
Tail fin resorbed
Thyroid follicle maturation
Keratinized skin
Palate bones resorbed
External gills resorbed
During and/or after metamorphosis, what happens to Anurans?
Limbs develop
Tail lost
Skull bones develop
Branchials resorbed
Tail fin resorbed
Thyroid follicle maturation
Keratinized skin
During and/or after metamorphosis, what happens to Gymnophionans?
Tentacle develops
Thyroid follicle maturation
Keratinized skin
Palate bones resorbed
External gills resorbed
During and/or after metamorphosis, what happens to Caudates and Anurans?
Branchials resorbed
Tail fin resorbed
Thyroid follicle maturation
Keratinized skin
During and/or after metamorphosis, what happens to Anurans and Gymnophionans?
Thyroid follicle maturation
Keratinized skin
During and/or after metamorphosis, what happens to Gymnophionans and Caudates?
Thyroid follicle maturation
Keratinized skin
Palate bones resorbed
External gills resorbed
During and/or after metamorphosis, what happens to all amphibians?
Thyroid follicle maturation
Keratinized skin
Which organ detects pheromones in Caudates? What are pheromones used for?
Vomeronasal organ; to attract mates
What about the proximity of the vomeronasal organ to the mouth suggests its importance?
The vomeronasal organ is very close to the mouth (used to aid in olfaction), which indicates it is very important for the detection of pheromones
Link the loss of the tympanum to the emphasis of pheromones in Caudates
Frogs rely on sound for attracting mates, so they need to detect both high and low frequencies (need tympanum). Salamanders use pheromones to attract mates, so they don’t have a use for hearing high frequency sounds
How must the pheromone mate-attracting system be balanced in Caudates?
Must be strong enough to attract a mate but not predators, so the development of the vomeronasal organ aids in this detection
Which reproductive strategies do Gymnophionans use?
Oviparity, viviparity, ovoviviparity
What is maternal dermatophagy? What amphibian clade uses this?
The young feed on the nutrient and lipid-rich skin of the mother (externally and internally in the oviduct); Gymnophiona
Which mating call indicates a higher fitness? Why?
A whine with multiple chucks indicates a high level of fitness because it is most likely to attract predators. This shows that the frog is able to escape predation despite advertising its own location
Which frequency (high or low) is used for frog mating calls?
High
What were the early experiments in developmental timing? Results?
Axolotl’s external gills were excised, which led to death in most subjects, but metamorphosis in 2/11 of them
What is heterochrony? Example?
The modification of the relative timing of developmental processes to impact the phenotype of an organism; neoteny
What is heterotopy? Example?
The modification of the relative spacial regulation of developmental processes to impact the phenotype; transition of fin to limb
What are the subdivisions of heterochrony?
Paedomorphosis and peramorphosis
What is an example of peramorphosis?
The metamorphosis of tadpoles in different species
True/False? Amphibian diversity is a poor indicator of the overall health of an ecosystem
False. They are sensitive to climate change, pollution, invasive species, diseases, salinity, etc. so they can indicate if an ecosystem is under stress
Is there a way to cure chytridiomycosis? How and why?
Amphibians may only be cured if they undergo high temperatures, which will kill off the fungus
Why are humans unaffected by chytridiomycosis but amphibians are?
Humans are homeothermic endotherms, so we maintain a constant and hot body temperature which is too hot for chytridiomycosis to survive
What is the major theme for the synapomorphies of Anura?
Focus on characters for jumping
What is the major theme for the synapomorphies of Caudata?
Basal characters of amphibians
