AD amphibians Flashcards
Reptiles vs amphibians
Reptiles =
Typically dry and scaly skin - skin enables them to live in dry areas Nearly all lay eggs/bear young on land Young are miniature replicas of adults from birth / hatching – no larval stage
Amphibians =
Typically moist skin, lacking obvious scales. - thin, permeable skin allows gas exchange, but also rapid water loss so tend to live in moist environments Nearly all lay eggs in water Distinct 2 stage life cycle
Describe reproduction in amphibians
In all three Orders, examples of eggs hatching
within mother, young consuming yolk or
maternal tissue
What are the orders of amphibians?
Anura (frogs and toads)
Caudata / Urodela (salamanders & newts)
Gymnophiona / Apoda (caecilians) = worms
How do amphibians breathe?
Fish can breathe air - Air breathing organs evolved
independently many times in bony fish
• Some amphibians can’t - Hundreds of spp. of urodele
never develop functional lungs
• Presence of lungs, and gills, varies widely. Cutaneous
gas exchange is almost without exception. It occurs in
eggs, larvae and adults, in air and water, in all three
orders.
Describe the Permeability of the skin &
osmoregulation
Amphibians have relatively permeable skins – but
evolution towards less permeability assumes that
permeability is a disadvantage
• Permeability likely to be an evolutionary advantage:
allows transcutaneous rehydration (e.g. via
specialised skin patches); cutaneous gas exchange
with no energetic cost of ventilation
Why are there so few amphibians in the uk?
20,000 yrs ago: Ice sheet covering much of Europe. Sea level ~
100 m lower, land bridge connecting Europe & Britain. Herps in
Mediterranean refuge – none in Britain – too cold
10,000 yrs ago: warming allowed herps to move N. Some species
> Britain.
8,000 yrs ago - rise in sea levels - land bridge flooded. Ireland cut
off first – no snakes, no common toad
Describe some well established ‘aliens’
1) Marsh frog – most successful alien so far – largest
European anuran. Abundant in some areas of SE
2) Edible frog – co-occurs with marsh frog, similar
habits
3) Midwife toad. Males carry eggs. Introduced in
Bedford with garden plants, late 1800s
4) Alpine crested newt – many areas, e.g.
Surrey, Sunderland, Shropshire
Describe the courtship of frogs and toads
“Explosive breeders”
- all migrate at once, or within short space of time
– grab, hope for the best
Describe the courtship of newts
More prolonged, arrive over period of months. Very temperature dependent Becoming earlier
Pheromones – proven to be an important component in newt courtship
Complex series of manoeuvres – male leading female to pick up spermatophore via her cloaca
Describe egg laying
Toads – swim in amplexus. Slow stretching movement prior to starting – may take many hours (7-10 feet, 3-4000 eggs)
Frogs – rapid ejection of ~ 2000 eggs (takes a few seconds), female pushes on abdomen.
Fertilisation external – male sheds sperm over eggs as laid
Initially un-swollen – sperm can penetrate – jelly absorbs water and expands
Newts = Eggs wrapped - individually in leaves of plants close to water surface (~250 eggs). Several per day – process v prolonged
What role do amphibians play in the ecosystem?
• Adult and larval amphibians are important
predators of invertebrates. Removal of amphibians
can cause massive increase in insect populations.
• Important role in nutrient cycling - through
movement from aquatic to terrestrial habitat, many
species of frogs and salamanders act to transfer
nutrients from aquatic systems to terrestrial ones
Describe defense mechanisms in amphibians
Some amphibians eaten as a
delicacy, e.g. frogs legs
Others so toxic that to touch may
be fatal
Describe global declines in amphibian population
• One-third of amphibian species threatened (IUCN Red List)
• Habitat loss, alternation, fragmentation
• Introduced species- direct competition, and sources of
disease
• Over-exploitation e.g. as food, pets, medicinal
• Climate change – sensitivity to changes in temp and moisture
• UV-B radiation – immune disfunction, reduced growth
• Chemical contaminants – direct mortality, and sublethal
effects inc developmental/ reproductive / behavioural
abnormalities
• Disease e.g. chytridiomycosis ** suggested topic for further
reading
• Deformities – widespread increase
• Synergisms - multiple stressors act together
Describe how amphibians are important in medicine
• Regeneration of limbs - hope for understanding how we
may be able to understand potential human ability to
regenerate lost cells / tissues / organs?
• Peptide caerin 1.1 from Litoria caerulea inhibits growth of cancer cells, viral infection of target cells, prevents growth of malaria parasite, and kills nematodes.
• Alkaloid epibatidine from the endangered Ecuadorian
frog Epipedobates tricolor is a potent non-addictive
analgesic considered to be 100 to 200 times more effective than morphine
