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Life in Freshwater

Common Frog (Rana temporia)

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The Common or Grass Frog is the most widespread Brown Frog in Europe. It is variable in colour and markings. The ground colour may vary from greyish through to yellow-brown to reddish with darker markings across the hind legs on the backs. There is usually a pair of angled dark marks between the shoulders forming a forward pointing V. At metamorphosis froglets are about 12-15mm. They may grow to an adult length of 10cm but 6-7cm is a more typical body length.

The Common Frog is abundant and widespread. It is often found at high altitudes, even up to the snowline, especially in southern Europe where it avoids lowlands. Cold-blooded vertebrate. Females are usually larger than males.

Except during the breeding season, most frogs live on land amongst damp herbage often some distance from their ponds; hence the European name, 'Grass Frog'. When young males often overwinter in the water.

ECOLOGY: Studies have shown that the Common Frog will eat any invertebrate found on land as long as it is a suitable size to be swallowed. Its diet changes throughout the year as the abundance of various insects, spiders, harvestmen, molluscs and caterpillars change with the seasons.

The Common Frog is also an important prey species in many food chains. Predators include grass snakes, otters, rats, badgers, stoats, weasels, hedgehogs, herons, storks, hawks, owls, gulls, ducks and corvids. Other species also predate frog tadpoles.

Typically in late March to mid-April frogs reproduce. The male grasps the female when in the water and squeezes the side of the body to trigger the release of up to 3000 eggs at a time from her body. He releases sperm over them as they are laid. The mass of eggs usually decend to the bottom but later float to the surface. Frog spawn development:

1. Frog spawn - Cell division soon results in a ball of cells in which the individual cells are too small to see with the naked eye but within a few days, depending on the water temperature, the embryo changes shape. Gradually feature such as external gills and tail become obvious.

Developing frog spawn

2. Frog tadpole: After about two weeks the tadpole wriggles free from the jelly but remains attached by a pair of adhesive organs just behind the mouth whilst further development is completed. At this stage the tadpole uses external gills for gaseous exchange. Rasping 'teeth' form for feeding on filamentous algae and other plant material.
Frog tadpoles

3. Frog tadpoles: By about the fifth week hind legs start to develop and a change from plant food to animal food may take place. Note that newt tadpoles develop the front legs first. The external gills have already been replaced by internal ones. Now lungs start to develop. Frog tadpoles can be distinguished from toad tadpoles by their speckled appearance.
Frog tadpole

4. Frog tadpole: After about 12 weeks the tadpole stops feeding. The outer skin is shed, the mouth widens, a tongue forms, and eyelids develop. The fore limbs grow out from the body. The gut becomes shorter and the tail is gradually re-absorbed to provide nutrition whilst metamorphosis occurs.
Common Frog

5. Common Frog: Frogs vary in colour and markings which are controlled by pigment cells (chromatophores) in the deeper layers of the skin. Lipophores contain fatty granules of yellowish pigment and are responsible for yellow and red colours, guanophores contain crystals of guanine and appear white and melanophores contain the dark pigment melanin and look black or brown. The abundance and grouping of different types of chromatophore are not the only factors controlling the colour since the ground colour can vary according to whether the melanin is dispersed or compacted within the melanophore. Albino frogs, like other albino animals, lack melanin but are coloured yellow instead of white because the skin still contains lipophores. Adult frogs obtain oxygen in three ways: from diffusion of gases across the skin, in a primitive pair of lungs and through the membrane at the back of the throat.











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