Saturday, May 06, 2006


The order Anura is an order in the class Amphibia that is comprised of toads and frogs which are referred to as tailless amphibians1. The word Anura is derived from a Greek an-without oura-tail hence tailless2. Frogs have no tails except for their larval stages called the tadpoles. They exhibit both terrestrial and aquatic lifestyles and depend on water for reproduction2. They are distributed in tropic and temperate areas of the world occupying diverse habitats. By evolving to live on land the frogs have adapted to escape the predation of their egg in the aquatic environment where they are more vulnerable than on land. On land they have also enemies which include invertebrates (especially ants and spiders) which feed on their eggs vertebrates like snakes and small mammals which feed on the young1.

Various methods have been adopted by anurans in order to protect their young and eggs predation and enhance chances of survival in terrestrial environments. This is a form of parental care exercised by the anurans. The Families Rhacophoridae, Hylidae, Hyperoliidae, Leptodactylidae and Myobatrachidae build foam nests that are used to harbour their young4. The genus Chiromantis which is found in Africa is an example, which builds nests on tree branches near water, by the female excreting a liquid which is beaten into a froth ball by the male. Eggs are laid in the froth which hardens to retain moisture. The eggs hatch into tadpoles and have moisture constantly added by the female. Later the tadpoles drop from the froth ball when it softens and drop into water4.

Others like Pipa carvoelhi (a toad) after mating have fertilised eggs picked by the male frog on the hind legs and spread on the female’s back where they are embedded and a membrane forms to cover them. The tadpoles hatch and develop and break from the skin. Others of the Genus Afrixalus (leaf folding frogs) lay eggs in leaves where they are fertilised and then the frogs fold the leave and sometimes grasses with a sticky substance which keeps them trapped till they hatch and the glue loosens and they are released into water3.

The Nectophrynoides of Western Africa have internal fertilisation and the eggs develop in the female’s oviduct to maturity and the frog gives “birth” to froglets. The Chilean frog Rhinoderma buries her eggs on moist ground and is guarded by the males who later take them into their mouths (vocal sacs) till they mature into little frogs. One of the poisonous Phyllobatids of South America lay eggs near males who guard them till they hatch. They later take the tadpoles on their backs and produce mucous which covers the eggs till they mature. An interesting method of parenting is practised by the Australian frogs Rheobatrachus silus and Rheobatrachus vitellinus. The female swallows the eggs after fertilization brooding them in her stomach for six weeks. To avoid the eggs being digested by the digestive juices it’s thought a substance (prostaglandin E2) is secreted by the egg capsules and then by the tadpoles which stops digestion. They feed from the york of the eggs and mature to adults where they ‘born’ in a process to mammalian birth because of the contractions but through the mouth4.

Europe’s midwife toad (Family Discoglossidae) lives in holes close to water but mates on land. The eggs are in strands are fertilised and are twisted on the males hind legs till they are about to hatch and they are taken to water to continue their life there4. Another form of parenting is practised by a small frog in Brazil which builds its own pond with mud to lay eggs and the tadpoles mature in the ponds. As the rains persist the ponds are flooded and the tadpoles swim into other bigger water bodies4. Whereas the above mentioned anurans only need to utilise water that’s readily available their counterparts in desert areas had to evolve and adapt to survive with little not readily available water. They had two problems to handle escaping predators (together with the young) and also be able to utilise the scarcely available water.

The African Breviceps is a burrowing group of frog which lives in arid areas but mate when there’s a heavy rain where also the female takes in a lot of water. They have bigger females and smaller males, and fertilisation occurs with the males gluing on the females back1, 4. In this position the female burrows and lays the eggs which are fertilised by the male. Constantly the female sprays moisture onto the eggs from her bladder till the froglets hatch4. The spade foot toads in the Western Deserts of USA have tadpoles developing within two weeks or less to small frogs. The water-holding frog, Cyclorana of the central desert regions of Australia mate and lay their eggs in tepid shallow pools of water. They rapidly develop from egg, tadpole and into froglets then take as much water before burrowing deep into the sand and secrete a membrane around them to prevent them from water loss4. This way they are able to survive long dry spells in the desert.


1. Duellman, W. E. and Trueb, L. 1986. Biology of Amphibians Philippines: McGraw-Hill, Inc..

2. Wikipedia contributors. Frog [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 4, 14:56 UTC [cited 2006 May 6]. Available from:

3. Carruthers V. 2001. Frogs and Frogging in Southern Africa. Cape Town: Struik Publishers (Pty) Ltd

4. Knight, R. BCB Biodiversity chapter 2 The Invasion of the Land (Cited 2006 May 6)


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  • Hey Vincent

    You cover the subject very well, and your piece is well-structured and interesting. I would've appreciated an explanation as to the probable causes of the diversity of parental strategies (in terms of evolutionary theory), but that's okay.


    By Blogger NcK, at May 17, 2006 10:56 AM  

  • Hii, Vincent, nice work.According to me you have covered a topic very well. e.g frogs are amphibians and they lay their legs in water.

    By Blogger linette, at June 01, 2006 4:12 PM  

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