Lethabo

im 22 years old, female doing my honns in ecological informatics at csir(pretoria)

Name:
Location: pretoria, gauteng, South Africa

i completed my Bsc (microbiology physiology) degree in 2005 at University of Limpopo, now im doing my honns in ecological informatics at university of the western cape.

Tuesday, May 16, 2006

ADAPTATION REQUIRED TO MAKE THE TRANSITION FROM AN AQUATIC TO A TERRESTRIAL ENVIRONMENT- AMPHIBIANS

In general Amphibians are ectotherms and spend part of their time on land. They live both in water and on land but they spend most of their time in water. Amphibians are soft bodied; they are hunted after as food by larger predators. The common European Toad (Bufo bufo) inflates its body and stands on its toes to appear as large as possible and thereby discourage any potential predator. More active defence occurs in the fire-Bellied toad produce a mucous for protection which keeps the skin moist and it is also extremely bitter tasting. The poison (mucous) which frogs produce is lethal to mammals and local people use its poison to tip their arrows. Defence that frogs use-producing a poisonous mucous- it is of a little value because their attacker dies after they themselves have been eaten.

When amphibians are in water they use gills to breath but when on land the gills are replaced by other respiratory organs i.e. lungs. They change their skin and develop glands in order to avoid dehydration. Amphibians eyes develop eyelids and adapt to vision outside the water. An eardrum develops to lock the middle ear and the tail disappears.

Limitations to an amphibians terrestrial life

Amphibians are only partly successful in their colonization of land, since their limbs are short and they need to flex their body in order to take reasonable strides. Their skin is permeable and in dry atmospheres they dehydrate quickly. Amphibians do not have the mechanisms to drink water while they are on land. Their skin must be moist in order to supplement respiration since their lungs are comparatively simple and not totally adequate for its needs. These limitations restrict amphibians to moist environments. Amphibians are entirely dependent on water for reproduction sine their eggs have no water-proof covering and their larvae (tadpoles) which are quite like fishes. These larvae initially have no legs they use their long tail in order to swim and they use external feathery gills to breathe.

Amphibians use terrestrial environment mostly for laying eggs you have just said they lay their eggs in the water? Because for them it is a much safer site for the development of their offspring than an aquatic environment which has many predators (especially fish). Anurans have evolved mechanisms to exploit the terrestrial environment for the breeding of their young. Some amphibians like the midwife toad Alytes obstetricans live in holes close to water and mate on land. After fertilization the long strands of eggs are twisted around the hind leg of the male toad. The male carries them around until the tadpoles are ready to hatch and then takes them to water.

In dry habitats, amphibians development is limited by moisture not by temperature. For example the rain frogs Breviceps which live in dry regions only come (out of burrows) above ground during heavy downpours. Adults emerge from their underground burrows and absorb rainwater through their skins, thus replenishing their body fluids. Amphibians fill their bladder with water. Some frogs are able to hold water; they minimize their dependence on water under dry conditions. When it rains they absorb lots of water and bury themselves deep inside the sand and then they secrete a membrane around themselves which prevents water loss.

Many frogs are able to absorb water directly through the skin, especially around the pelvic area. However, the permeability of a frog's skin can also result in water loss. Some tree frogs reduce water loss with a waterproof layer of their skin. Others have adapted behaviours that conserve water, including engaging in nocturnal activity and resting in a water-conserving position.

References:

1. Wikipedia contributors. Amphibians [Internet]. Wikipedia, The Free Encyclopedia; 2006 Mar 27, 22:44. PTA [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Permeable
2. Wikipedia contributors. Amphibians [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 9, 00:20. PTA [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Amphibians
3. Wikipedia contributors. Amphibians [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 9, 02:38. PTA [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Frog
4. Wikipedia contributors. Amphibians [Internet]. Wikipedia, The Free Encyclopedia; 2006 Apr 30, 18:42. PTA [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Nocturnal
5. Wikipedia contributors. Amphibians [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 9, 03:32. PTA [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Microhylidae
6. Wikipedia contributors. Amphibians [Internet]. Wikipedia, The Free Encyclopedia; 2006 Feb 8, 17:35. PTA [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Midwife_toad
7. Wikipedia contributors. Amphibians [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 9, 02:38. PTA [cited 2006 May 9]. Available from: http://en.wikipedia.org/wiki/Anurans

Lethabo Mosomane
CSIR
Pretoria
0001
Tel: 27 12 841 2133
Fax: 27 12 842 3676
mail: lmosomane@csir.co.za
http://lmosomane.blogspot.com

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