The Book of the Frog by Sally Coulthard

Author:Sally Coulthard
Language: eng
Format: epub
ISBN: 9781803287980
Publisher: Bloomsbury Publishing Plc
Published: 2024-06-15T00:00:00+00:00

The alternative reproductive strategy employed by frogs is ‘prolonged breeding’. Some species that inhabit regions that are hot and humid all year round, such as the tropics and subtropics, space out their breeding sessions at regular intervals during the year. While explosive breeding tends to result in an unseemly scramble, males of prolonged breeding species often use a different approach. They call from a stationary position, usually their own patch of territory, and prefer to keep a distance from other males. And, rather than attempt to play the ‘numbers game’ by grasping at as many females as possible, the prolonged breeder often waits for a mate to approach him. That doesn’t mean a prolonged breeding male won’t attempt to woo more than one female; he’ll just do it methodically, one at a time.

In most species of frog, the female’s eggs are fertilised externally. The male and female frog need to be in close contact so he can fertilise the eggs as she releases them. During mating, in many species of frogs, the male climbs on top of the female and ‘piggybacks’, holding her close to his body with his forearms. This is called amplexus, a tight embrace that coordinates the sperm being released onto the eggs. To help him hold on, a male often grows temporary ‘nuptial pads’ on his thumbs and forearms. Triggered by hormones, these super-grippy swellings help the male suitor cling on until the mating is complete.

The number of eggs laid by a female frog can vary hugely. While some species release just a handful, others lay thousands upon thousands. The enormous cane toad, for example, can lay up to 25,000 eggs in one clutch, while some species of poison dart frog will pin all their hopes on a tight brood of fewer than five. Both the European common frog and the common toad lay similar amounts of eggs – between a few hundred and a few thousand – but in easily distinguishable spawn. While the common frog leaves a gloriously jelly-like wobbly clump, the common toad’s eggs are laid in a string, delicately draped around a pond’s vegetation.

The common rain frog of South Africa, however, has some inherent design flaws when it comes to mating. Both sexes have plump, round bodies and very short limbs, making it tricky for the male to grasp on to his mate. The male is also dramatically smaller than the female, resulting in mating attempts that can look like a marble trying to balance on a tangerine. But nature is ingenious. Researchers have recently discovered that both sexes produce a sticky glue that bonds them together. The male secretes gum on his chest and arms, while the female makes her back sticky, allowing both to maintain amplexus for up to three days or enough time for the eggs to be fertilised. After that, the ‘love glue’ loses its adhesive quality and the pair unpeel to go their separate ways.23

In explosive breeding species, males can behave aggressively and attempt to physically separate other couples already engaged in amplexus.

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