Amphibians Flashcards
Describe the class amphibia
- aquatic / terrestrial
- 3 extant orders within subclass Lissamphibia, shared derived characters in skin, eyes, ears, teeth
What are the 3 extant orders in the subclass Lissamphibia?
- anura - frogs and toads
- caudata - salamanders and newts
- gymnophiona - caecilians
Describe aquatic larvae
- biphasic life history with metamorphosis
- obligatorily aquatic larvae - facultatively terrestrial adults
- lateral lines
- gills
- fish-like circulatory systems
Describe gills in aquatic larvae
- external in embyonic stage
- internal until metamorphosis in anurans
What is a classic Paleozoic amphibian example?
- Archegosaurus
- Larva 15cm, adult 1.5m
- series showing less external gills over growth, increased skeletal growth
- bony dermal scales unlike Lissamphibians
What are the possible evolutionary origins of modern Lissamphibians?
- Temnospondyls: carboniferous - early cretaceous
- Lepospondyls: carboniferous - early permian
What is the paedomorphism hypothesis of anuran origins?
- retention of larval characters in an adult organism
- juvenile characters of anurans:
- miniature in size
- preorbital skull short with broad rounded snout
- relatively large orbits
What is the derived character of subclass Lissamphibia?
- Greek lissamphibia - smooth skin
- members of all 3 orders have skin that lacks scales, kept moist by mucus glands, permeable and contains poison glands
Describe cutaneous gas exchange in amphibians
- can obtain 20-95% oxygen through skin
- 2/3 CO2 excretion through skin
- continiously in both air and water
- some needed in water
What are examples of amphibians that are needed in water for gas exchange?
- many ranid frogs semi-aquatic
- pipidae entirely aquatic
- northern temperate frogs hibernate in water using cutaneous gas exchange
Describe amphibian skin
- outer epidermis and inner dermis
- epidermis lightly keratinized and multi-layered
- glands present
- chromatophores in dermis
Describe the lightly keratinized and multi-layered epidermis
- thin outer layer of dead cells, little water resistance, periodic moults
- layer of keratinocytes, limiting barrier for solute and water transport
- lower layer regenerates epidermis
What is an example of amphibian epidermal disease?
Chytridiomycosis:
- chytrid fungus
- skin parasite - superficial keratin layers:
- increased sloughing, decreased osmotic regulation
What glands are present in the amphibian dermis?
- mucus
- poison
- bioactive secretions
Describe mucus glands in amphibians
- slippery and slimy mucus
- contains mucopolysaccharides and mucoproteoglycans
- moist surface to increase gas exchange & decrease water loss and friction
- increased body temp leads to mucus discharge
Describe poison glands in amphibians
- granular
- secrete bioactive compounds, some from arthropod prey
- e.g., alkaloids, bioactive peptides
What are the functions of bioactive secretions?
- anti-microorganism
- anti-oxidation
- anti-predation
- neuroendocrine regulation
- imunoregulation
- mating
- anti-parasitism
- wound healing
- analgesia
Describe the different chromatophores present in amphibian dermis
- dermal chromatophore unit: triple cell structure
- zanthophore - yellow
- erythrophore - red
- iridophore - blue or white
- melanophore - black/brown
Describe how iridophores give blue or white colours
reflective platelets (purine crystals) scatter light
Describe how rapid colour changes occur in amphibian dermis
- when frog darkens: melanosomes migrate around iridophore
- hormonal controls
- dimensions of iridophore platelets can change
Describe chromatophore mutants with transparent skin
- mutation to lose melanophores and iridophores
- melanophore only loss is red
- iridophore only loss is brown/black
- double mutant has transparent skin
- white peritonea on some organs, gall bladder transparent yellow and ova green
Why are poison frogs variable colours?
bright colours advertise toxicity to predators - aposematism
Describe the evolution of Early Triassic vs Modern Anuran skeletons
Early Triassic -> Modern Anuran
Short ilium -> Elongated ilium
No urostyle -> Urostyle
14 presacral vertebrae -> 5-9 presacral vertebrae
No tough sacral region -> Toughened sacral region
Shorter hindlimbs -> Longer hindlimb
Short tarsals -> Elongated tarsals
Tibia and fibula separate -> Fused tibia and fibula
Radius and ulna separate -> Fused radius and ulna
What do the adaptations of modern anuran allow for?
better jumping
Describe the evolution of anuran pelvic and thigh muscles
- tail muscle of caudate - anuran urostyle muscle for dorsal rotation
- semimembranosus pelvis to knee in both
- strong muscle for initial phase of jumping, swimming, walking
What is the difference between Anurans and Caudates?
caudate - vertebrate with a tail
anuran - no tail
Describe the anuran pectoral girdle
- complex and flexible girdle absorbs impact on landing
- derived elements highlighted
- structural variations used in frog taxonomy
Describe the locomotion of landing in American bullfrogs
steep and fast takeoff
land first on extended forelimbs -> belly -> feet:
- belly hit, legs flexing
- legs mostly flexed and feet slap
- legs/feet elevated and hips flexed
- feet put down, toes held up
- toes put down
Describe the evolution of basal frog ‘belly flop’ landing
rocky mountain tailed frog - slow and flat take-off
land on belly - same limb positions as takeoff
- body hits, limbs extended back
- movement stopped, hands going forward
- hands down, legs protracting over body
- legs/feet elevated, hips flexed
- feet put down, toes held up
- toes put down
Describe the body characteristics of aquatic frogs
- swim using powerful hindlimbs
- lack tongues and teeth
- suction feeding
- forelimbs manipulate prey
- clawed hindlimbs tear prey apart
- retain lateral line as adults
Describe the anuran body characteristics of tree frogs
- several families - convergent evolution
- tiny with long limbs
- many change colour for camoflage
- forward facing eyes
- adhesive pads on digits
Describe the highly derived anuran cranium
- several typical tetrapod elements lost or fused
- most of skull roof - frontoparietal complex
- palate highly fenestrated
- lacks dentition
- frontoparietal - fusion of 2 bones at top
- wide orbits for sunlight
Describe amphibian eye bulging muscles
- retractor bulbi retracts eyeball into buccal cavity - pushes food into oesophagus
- levator bulbi eyeball after swallowing
- use fenestration in cranium
Describe anuran vision
- large and protuberant - 360 degrees of vision
- binocular vision of over 100 degrees to front
- prey detected by movement and contrast
Describe lingual feeding in anurans
- protrudable tongue attached at lower jaw front
- pivots around muscle - flipped out
- prey adheres to sticky mucus
- aquatic frogs lack tongue - use suction
Describe the organs present in the body cavity
- liver - dark lobes
- stomach and intestine tubular
- fat bodies - yellow filamentous structures
- urinary bladder - large structure at posterior
- lungs ‘underneath’ pectoral bones
Describe water homeostasis in anurans
- in dehydrated frog hypothalamus - increased AVT
- antidiuretic peptide hormone leads to increase aquaporin water channels in kidney, urinary bladder, pelvic skin
- frogs sense and do not sit in hyperosmotic water
Describe the lung structure in frogs
gas exchange at alveoli between raidal folds that project into lumen
simple structure
Describe buccal pump breathing and ventilation
- narrow vocal slits on each side of buccal cavity - elastic vocal sac chamber
- inspiration: buccal cavity expands, air drawn into cavity
- expiration: buccal cavity contracts, air forced out
Describe the 3 chambered heart in diving/hibernating frogs
- right atrium: oxygen rich blood from cutaneous respiration
- longitudinal baffle in outflow tract - decreased mixing of 2 flows
- single ventricle pumps flood from both atria
- if underwater: vascular constriction of pulmonary circuit - flow down left atrium
- if lungs in use: pulmonary circuit - increased flow via left atrium
Describe the female organs in amphibians
- ovaries beside kidneys
- bulge with ova if gravid
- ova pass down pair of ovidcuts to cloaca
Describe male organs in amphibians
- testes attached to ventral surface of each kidney
Describe fertilization in amphibians
- external fertilization: cloacal apposition in most anurans
- amplexus - male on back of female
- male forelimbs wrapped round her body - stimulates female to release ova as spawn
- sperm ejaculated from male cloaca onto eggs as female lays them
