Anurans

Question 1

Anuran morphology

Answer 1

•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

Question 2

Anuran skeletal modifications

Answer 2

•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

Question 3

Differences between frogs and toads

Answer 3

•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

Question 4

Generalised life cycle

Answer 4

1. Aquatic phase - egg develops
2. Larva hatch (aquatic still)
3. 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

Question 5

Trends in reproductive diversity

Answer 5

•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

Question 6

Foam nests

Answer 6

• 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

Question 7

Terrestrial eggs on leaves

Answer 7

•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

Question 8

Tadpole development and parental care

Answer 8

• 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

Question 9

Posion-arrow frogs

Answer 9

•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

Question 10

Finding a mate

Answer 10

• 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

Question 11

Problems with mate finding system

Answer 11

• 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

Question 12

Experiment on predator/call trade-off

Answer 12

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