Amphibians Flashcards
When did amphibians rise?
Palaeozoic era, during the Devonian period (420 - 360 MYA)
The amphibians were the dominant terrestrial vertebrates during what period?
Carboniferous
What orders are within amphibia?
Anura (frogs & toads)
Urodeles (salamanders & newts)
Gymnophionans (caecilians)
How can you distinguish Anura, Urodeles and Gymnophionans?
Briefly explain
Locomotor adaptations
Anura: long hind limbs; short, stiff bodies; HOP
Urodeles (Caudata): equal-sized limbs; long, slender bodies; WADDLE
Gymnophionans (Apoda): no limbs; long, slender bodies; SLITHER
How many families are in Anura?
29
How many families are in Urodeles (Caudata)?
10
How many families are in Gymnophionans (Apoda)?
6
What percentage of all amphibians does Anura make?
88%
What percentage of all amphibians does Urodeles (Caudata) make?
9%
What percentage of all amphibians does Gymnophionans (Apoda) make?
3%
Name at least three changes that occur in the transition from aquatic tadpole to terrestrial frog
- Small mouth for algae feeding replaced with large mouth for catching prey
-Tadpole gut, herbivorous; adults have a short gut to compliment carnivorous diet - Development of legs
- Development of lungs
- Degeneration of gills
- Degeneration of tail
MANY MORE CHANGES
What are the three periods of change during the metamorphosis from tadpole to frog
- Pre-metamorphosis: tadpoles increase in size, little change in shape
- Pro-metamorphosis: Hind legs appear, growth slows down
- Metamorphic climax: fore legs emerge and tail regresses
What is amphibian metamorphosis controlled by?
It is controlled by hormones and associated receptors in response to environmental cues.
What is the environmental cue to initiate metamorphosis?
Day length
What are the shared derived characteristics of modern amphibians supporting monophyly?
- smooth, moist skin
- multiple methods of respiration
- pedicellate teeth
- green rods (vision)
- operculum - columella complex (hearing)
- levator bulbi muscle
Briefly describe the smooth, moist skin found in modern amphibians
- Absence of bony/keratinised scales (caecilians are the exception)
- Absence of keratinised, true claws
- Mucous glands (prevent desiccation/slippery)
- Poison glands; Concentrated on dorsal surface; Produce a diverse array of chemicals
Name at least three methods of controlling water loss
- Behavioural modifications; e.g. common tree frog: cool, wet nights they are active & inactive during warm, dry days
- Pelvic patch; highly vascularised ventral skin; absorbs majority of water
- Permeable bladder; store dilute urine; “canteen” away from water
There are multiple methods of respiration, what are they?
Briefly explain.
- Cutaneous : Gas exchange occurs across moist skin
- Buccopharyngeal: Gas exchange occurs in buccal cavity/pharynx
- Pulmonary: Gas exchange occurs in paired lungs
- Gills: Larval forms and noetenics
What is meant by the term “neoteny”?
Adults retain juvenile characteristics
e.g. Axolotl
Name three issues amphibians may have with respiration.
- Amphibian lungs are too small for all gas exchange
- Amphibians lack intercostal muscles between ribs so cannot expand and contract this changes air pressure
- Amphibians lack a diaphragm muscle
How do amphibians resolve the issues they face with respiration?
They use a BUCCAL PUMP, this forces air from the mouth to the lung. A strong hypobranchial apparatus in the floor of the mouth and throat allows this –> means air is pushed into the lungs
Briefly explain how amphibians breath.
- Air is drawn in to the buccal cavity with the glottis closed
- Nares close and the glottis opens
- Floor of the mouth is raised and the air is forced into the lungs
- This is repeated to fill the lungs with air
- Expiration may also be stepped process
POSITIVE PRESSURE BREATHING
Briefly describe pedicellate teeth
- Crown and base of tooth separated by uncalcified dentine/fibrous tissue
- May allow for “flex” of tooth for prey handling (all carnivores)
- Teeth break easily - continuously replaced
Briefly describe “Green Rods”
- Distinct type of retinal cell (photoreceptors)
- Amphibians are unusual among vertebrates in having two spectral classes of rod photoreceptors, unique amphibian “green” rods and typical vertebrate “red” rods
- Present in frogs and salamanders - caecilians are blind
Green rods are needed to maximise absolute sensitivity, visual acuity, and colour sensitivity
Briefly describe the unique hearing adaptation found in amphibians
OPERCULUM - Columella complex
- Two bones in middle ear that transmit sound to inner ear (via oval window)
- Dual high/low frequency system; high frequency = vibration of columella alone (air); low frequency = vibration of operculum-columella unit (ground) vibration via leg bones/scapula (activated by opercularis muscle)
- Predator/prey detection
What is the levator bulbi muscle?
- Muscle beneath eye
- Bulges eye outward; increases buccal cavity
- Used in breathing & swallowing
What are some additional characteristics of amphibians associated with the vertebrate transition to land?
- Skeleton and movement on land: Animals that live on land have to support themselves against gravity (limbs); Amphibian skulls are flattened, relatively small and have fewer bones than water-dwelling animals; The vertebral column lost much of its flexibility in order to transmit force from limbs to the body; Amphibians have a pelvic girdle - these bones attach pelvic appendages to the vertebral column –> very important in providing support on land
- Blood circulation - Amphibian 3-Chambered Heart; The right atrium pumps deoxygenated blood and the left atrium pumps oxygenated blood from the lungs and skin; Both atria empty into the single ventricle; The ventricle is divided into narrow chambers that reduce the mixing of the two bloods; When the ventricle contracts…. Oxygenated blood from the left atrium is sent to CAROTID arteries taking blood to the head (and brain)…. Deoxygenated blood from the right atrium is sent to the PULMOCUTANEOUS arteries taking blood to the skin and lungs, where fresh oxygen can be picked up; Blood passing into the AORTIC ARCHES has been thoroughly mixed, supplies rest of the body
- Nervous system and sensory function; The nervous system of amphibians is similar to that of other vertebrates; Their brain has 3 sections: FOREBRAIN; MIDBRAIN & HINDBRAIN; Amphibians have many sensory receptors on their skin; They can also have a lateral line system similar to fish and this helps aquatic amphibians; CHEMORECEPTION is an important sense for many amphibians, and caecilians - who are blind; SMELL is used in MATE RECOGNITION and in locating food, VISION is one of the most important senses for frogs and salamanders because they are primarily sigh feeders, often responding to the movements of their prey; The lower eyelid is movable, and it cleans and protects the eye; much of it is transparent and is called the NICTITATING MEMBRANE
What is the largest family in Gymnophionans?
Caeciliidae
What is the name for the family of truly aquatic caecilians?
Typhlonectidae
Name at least 3 general characteristics of caecilians
- Legless –> look like earthworms (live in soil or water) known from the early JURASSIC and earliest fossil had tiny limbs that completely disappeared in modern species
- ANNULATED bodies
- Tail is very short or absent
- Eyes have REGRESSED in many species
- CHEMOSENSORY structure (tentacle)
- Skull is very solid, with extensive suturing of cranial elements
- Dermal scales often present
- Operculum absent (no ear openings)
- Teeth are curved and relatively long compared to other amphibians
What percentage of offspring are thought to be oviparous in caecilians?
25%
What percentage of offspring are thought to be viviparous in caecilians?
75%
What is the largest family within Urodeles?
Plethodontidae - Lungless salamanders
Name at least 3 general characteristics of urodeles
- Trunk superficially segmented
- Presence of tail (larvae or adults)
- 4 equal sized limbs (extend at right angle from body)
Briefly describe the mating behaviour of urodeles
- Male spermatophore and internal fertilisation
- Most species have a typical biphasic life cycle and some guard their eggs
- Paedomorphosis (neoteny)
What is another word for neoteny?
Paedomorphosis
Sexual maturity reached without attaining full adult body form
Name at least 3 general characteristics of Anura
- Characteristic feature is their movement and skeletal features
- Hind limbs and muscle form a lever system that catapults the animal forward - Fibia and tibia are fused
- Posterior vertebrae are fused and form UROSTYLE
- Size varies from less than 2cm to >30cm
- Occur worldwide, except in the polar region, with a peak of diversity in tropical America
Briefly describe the mating behaviour of Anura
- Vocalisation to attract females (also fright calls before jumping into water and release/distress calls given if anuran grabbed by wrong sex or if captured by predator)
- Tendency to call in groups of 2-4 (i.e. chorus)
- Amplexus: the copulatory embrace of frogs and toads, during which the male fertilises the eggs that are released by the female (EXTERNAL FERTILISATION) - most frog species
- Highly diverse reproductive life histories, some trying to remove requirements for aquatic juvenile stage
What is unique about the suriname toad?
Suriname toad eggs are incubated under the skin on the female’s back, where they develop into toadlets which “hatch” by erupting through the females skin
What are the major reasons explaining the decline of amphibians?
ECOLOGICAL INDICATORS BECAUSE SO SENSITIVE.
- Habitat loss: fragmentation; conversion
- Environmental pollution
- Climate change
- Pathogens and disease
- Commercial harvest
What is the major disease threat to amphibians?
CHYTRID VIRUS
What is the difference between Salamanders, Newts and Sirens?
Salamander: a common name for the order of Urodeles, which includes 9 families
Newt: a common name applied to certain members of the Salamandridae family
Siren: common name applied to members of the family Sirenidae, which are aquatic salamanders that have no hind limbs
How are Salamandridae distinguished from other salamanders?
- Lack of rib or costal grooves
- Rough skin
What are the three native species of Salamanders in the UK & Ireland?
- Palmate newt
- Common (smooth) newt
- Great crested newt
What family is considered the “True frog family”?
Briefly describe.
Ranidae
- > 700 species
- No characters unequivocally diagnose Ranidae
- Most species lay aquatic eggs
- May be riparian, terrestrial or arboreal
- Ranids are cosmopolitan
- 5 out of 8 of the native anuran species belong to the ranidae family
What family is considered the “true toad family”?
Bufonidae
- > 100 species
- Cosmopolitan distribution, except Madagascar & Oceania
- Unique in having a BIDDER’S ORGAN - rudimentary ovary that develops at the anterior end of the larval testes of males and persists in adult males (i.e. paedomorphic characters)
- Prominent skin glands (PAROTID GLANDS) characteristic of many bufonids
- Most toads are terrestrial
- 2 out of 8 of the native anuran species belong to the bufonidae family
What is significant about the Alytidae family?
Midwife toads
- Primitive family of frogs, most are endemic of Europe
- Mostly terrestrial
- Male parental care: attaches egg clutches to their back and thighs and carries the clutch until the larvae are ready to hatch, at which point he releases the tadpoles into bodies of water
- Only one species in UK & Ireland belongs to Alytidae family
Briefly describe the Leptodactylidae family
- > 800 species
- Wildly heterogeneous group of frogs with no single synapomorphy –> probably multiple evolutionary lineages
- Occurs primarily in tropical America and West Indies
- Primarily terrestrial, foam-nest building frogs
Briefly describe the Hylidae family
- > 700 species
- Single known synapomorphy is claw-shaped terminal phalanges
- Most hylids are arboreal, with strong jumping skills
- Occurs throughout both temperate regions and tropical regions
