Anurans Flashcards
Anuran morphology
•lost tail and have more rigid body
•well developed limbs
•most diverse - aquatic and terrestrial forms
•reduced no. of digits
•increased hind-leg length to aid in swimming or for jumping both for predator avoidance
-locomotory advantage
•variations of hind and forelimb length affect locomotion mode
Anuran skeletal modifications
•shortened through loss of vertebrae - tail end had formed a urostyle
-supports pelvic region called the ilium = robust structure, providing support for jumping etc. almost like a shock absorber
•radius and ulna have fused to form the radio-ulan
•tibia and fibula fused to form the tibio-fibula
-both act as shock absorbers for jumping
Differences between frogs and toads
•frogs are often ambush predators - jumping on prey, need to be cryptic
•toads hop more - wide-ranging as can become conspicuous when looking prey
-not as cryptic as frogs though
Generalised life cycle
- Aquatic phase - egg develops
- Larva hatch (aquatic still)
- Change into more terrestrial forms - move onto land
Life cycle is only found in temperate regions
-vulnerable in water to predators, so selected to get out ASAP
Trends in reproductive diversity
•predation pressure on land is less than in aquatic habitats
•requires various adaptations against desiccation for gametes
•increasing egg and larval size enhances survival rate
-trade-off of fewer = more costly with longer development vs many eggs
•associated with various convergent methods of parental care like:
-foam nests
-eggs on water-overhanging trees
Foam nests
- secretions of the Fs oviduct
- M and F whip up through movement of hind/fore legs, has evolved 6 times independently
- can be both aquatic or terrestrial (ground and arboreal)
- protects eggs from desiccation and predation - tadpole development in foam is possible
Terrestrial eggs on leaves
•aquatic development of tadpoles, will fall into ponds when hatching
-evolved lots independently
•egg clutches sometimes folded into large leaves
•can be accompanied with guarding of egg clutches by males
Tadpole development and parental care
- some frogs have terrestrial tadpole development inside egg - high yolk content supplies food
- ovoviviparity - eggs develop in F oviduct but young nourished by egg
- mouth and stomach brooding - young develop inside adult
- Darwins frog - M swallows young that hatch into tadpoles (3-7 eggs laid) till ready
Posion-arrow frogs
•M are small (2-3cm) and have territories they defend of 100s m
•form terrestrial egg clutches and tadpoles hatch there
•climb onto parents back to be transported to aquatic site
•M or F involved in parental care (sex-role reversal and polyandry)
•small ephemeral water bodies usually predator-free but no food
-some spp tadpoles feed on unfertilised eggs
Finding a mate
- sex pheromones play little/no role
- nocturnal and crepuscular so not sight either
- tend to communicante acoustically
- stereotyped calls - spp specific
- calls produced by in or exhaling air on land or under water
- M only (some exceptions)
- vocal sac amplifies calls, radiation in circular directions
- can adapt call depending on social contexts
Problems with mate finding system
- calls only travel short distances, they aren’t long either
- attract predators too
- need to stand out from background noise (near flowing water with wave legs or arms)
- can be costly to produce
Experiment on predator/call trade-off
Song either a ‘whine’ or ‘whine+chuck’
F chose Ms that make more chucks
• If 1 M, will whine only
• More Ms = more chucks
• Predation risk increased with no. of chucks = trade-off
• As chorus size increases, predation risk decreases - advantage for complex song
