Topics 9 and 10 - Biology and Reproduction of Frogs

What is the Biology of Frogs?

• they are ectotherms (cold-blooded)

• they have moist skin for gas and water exchange

• they mainly eat invertebrates and anything that can fit in their mouth

• they have very little diet specialization

• most Australian frogs are nocturnal

• they mate through a call (only males call)

• females choose mates based on their call

• their mating embrace is called amplexus (they can mate in a number of different ways)

Types of Breeding Strategies

1. Standard (eggs and tadpoles in water)

2. Eggs not in water, than tadpoles in water

3. Eggs and tadpoles in moist depressions

4. Terrestrial clutch (eggs on land, tadpoles develop within eggs)

5. Hip pockets (tadpoles in skin pouches)

6. Gastric brooding

Explanation of different Breeding Strategies

Type	Explanation
Standard	Eggs and tadpoles in water. Usually large clutch sizes and no parental care.
Eggs not in water, then tadpoles in water	Eggs laid beside or above water. They develop, then inundate by rain or drop into water. Then typically tadpole life in pools/streams.
Eggs and tadpoles in moist depressions	Eggs laid in moist earth. Small clutches. Tadpoles lie around in wet nest and feed off yolk reserves.
Terrestrial clutch	Restricted in Australia to north QLD and south west Western Australia (predictable wet seasons). Small clutches. Tadpoles develop in eggs and froglets hatch out. Usually male parental care.
Hip pockets	In the Myobatrachidae family. Eggs laid and fertilised, guarded by male, eggs hatch, tadpoles wriggle into pouches on the side of male and feed on yolk reserves, and then froglets emerge.
Gastric brooding	Eggs fertilised externally, females swallowed the eggs, egg jelly contained a chemical that stopped secretion of stomach acid, eggs hatch into tadpoles, tadpoles developed in the stomach over a couple of months, frogs emerged from her mouth.

Advantages and Disadvantages of Aquatic and Terrestrial Breeding

Advantages of eggs and tadpoles in water:

• often huge numbers of eggs with little investment

• aquatic environments are rich in food

Disadvantages of eggs and tadpoles in water:

• requires water for some period

• plenty of predators

Advantages of strategies away from water:

• away from high predation

• higher success per egg

Disadvantages of strategies away from water:

• smaller clutch sizes

• requires more parental time investment