Frog Reproduction

Frog reproduction is pretty straightforward.  The adult comes into breeding condition around about Springtime, and they migrate to ponds where they pair up in a position known as amplexus.  

  • The female lays her spawn, the male releases his sperm at the same time to fertilise the eggs and, after the adults have left the water, the eggs hatch into tadpoles.  They eventually grow legs, lose their tails and come out of the water to make their home in the surrounding countryside.

This is a simplified account of frog reproduction, as it is in fact an incredible aspect of biology.

At each stage in the cycle, there can be variations, and up to half of the species, will depart from the conventional reproductive activity and do something completely different.

  • The frog reproduction cycle involve external or internal fertilisation; the eggs might be laid in the water, or they might not, and some species give birth to live young.
  • Before spawning can take place, the adult frogs need to be in a state of being able to reproduce.  This is determined by whether they feed well, and thus are able to produce the male and female sex cells.  In female frogs, this is eggs, or ova, and in males, it is sperm.
  • The pituitary gland is the gland that stimulates the production of these sex cells.  The pituitary gland itself is stimulated by external factors such as rainfall, day length and temperature.  

The frog reproduction cycle that happens at around the same time each year is known as cyclic breeding.  This means that their ovaries or testes follow a pattern each year.  

In areas where conditions are favourable and suitable for breeding, the breeding season is quite long compared to others.  For example, tropical frogs begin to breed at the beginning of the rainy seasons and will continue being able to breed until the start of the dry season.  This can be for as long as nine or even ten months of a year.  The males at this time will call every night, and the females that are ready to lay their eggs will visit the male frogs.  

Amplexus

Where there are species that do not share their habitat with other species, sometimes the male frog does not call

In general terms, a frog needs to own its own territory in order to attract a mate.  Male frogs do tend to go to huge efforts to make sure their territory is defined and well defended.  They use their call to let other males know that that particular territory is already owned.

In experiments, it has been found that a female will be attracted to the call which is loudest, and which goes on the longest.  

When the females arrive at the pond and enter the water, the male frogs will mill around and grasp at a ripe female.  

However, they will grasp at anything that is roughly the right size such as a piece of wood.  

Once the male lands on a ripe female he will often find that other males try to become involved, in which case the successful male will tend to kick away the others with a hind foot.  

The female will spawn and leave the pond, and the male will return to the other males in the hope of finding another mate.  

This goes on for a period of three or four nights, and gradually as the supply of females dries up, the males will desperse.

Frog reproduction: Amplexus (for more detailed information on amplexus click here)

Once the male has found a mate, he takes up a position in which he can fertilise the eggs.  This usually happens outside the female body, just after the eggs have been laid and before the jelly that will surround them has swelled.  To make sure that the male frog's sperm comes into contact with as many of the eggs as possible, he needs to position his cloaca as close as he can. This position is known as amplexus.

In order for the male frog to be able to keep a firm grip on the female frog so that he doesn't fall off during mating, most frogs have nuptial pads.  These pads have a rough surface and are often quite heavily pigmented. They form on the outer edge of the thumb of a sexually active frog or toad. These nuptial pads help prevent the frog from losing his grip during the mating act.

For more detailed information on Amplexus click here

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