THE ADAPTATIONS REQUIRED TO MAKE THE TRANSITION FROM AQUATIC TO TERRESTRIAL LIFE USING AMPHIBIAN AS EXAMPLE

The amphibians (example frogs) were "the first vertebrates that managed a footing on land" (1). Amphibians mean two lives, meaning that they can live in both water and land. They consist of a large group of different animals and frogs are the most familiar groups found in this class vertebrate. "Amphibians are particularly interesting because they are an example of the vertebrate body plan in transition between the aquatic and terrestrial environment" (2).

The transition from an aquatic life to terrestrial one, required modifications of several important body systems, to solve the problems of support and locomotion, gas exchange, desiccation, reproduction, feeding, and the function of some sensory systems. They adapted the different physical properties of water and air temperatures differences between water and land. They had to adapt with the drying out in the terrestrial ecosystem and had to change ways of giving birth. Transformation they had to change the way their circulatory system. When it comes to feeding, most amphibians feed well while they are in the aquatic environment. For example, crocodiles are very strong when they are inside the water when it comes to catching their pray.

The skeleton support was achieved by modification of the pelvic and pectoral fins and by strengthening the vertebral column. The skeletal support for the pectoral and pelvic fins was enlarged and strengthened, and the pelvic girdle became firmly attached to the vertebral column. The lower portions of the limbs were also greatly enlarged to provide an attachment area for powerful muscles. The vertebral column was strengthened by the development of interlocking processes and additional musculature.

The amphibians had to change their ways of locomotion for example in most fish, "the propulsive thrust is provided by the tail and caudal fin which push against the dense water that cause the fish to move forward" (2). In land the paired limbs with their strengthened girdles provided support for the body and also functioned in locomotion. When it comes to reproduction, amphibians had to adapt new ways of reproduction because reproduction in most frogs dependent on water as both fertilization and development. They adapted the way of excretion because most of these amphibians relied on large amount of water to wash away ammonia as excretory product. Therefore they had to use urea as their excretory product and it requires less water.

Although the amphibians managed to solve some changes, they were unable to solve one problem, reproduction in the terrestrial environment. . The problem is that the sperm, egg or developing embryo must be protected from desiccation. Amphibians must return to the aquatic environment to lay their eggs, and fertilize them, and it is there that the developing embryo grows until it is ready to move back up on land. Their adaptation from the aquatic environment to the land revealed a fantastic design that served them well in both environments.

References:

1. Four feet on the ground, [internet] [cited 2006 may 9] Available from:
http://oscar.ctc.edu/access/geology100/life3.html#anchor583986

2. The move to land, [internet] [cited 2006 May 9] Available from: http://instruct1.cit.cornell.edu/Courses/biog105/labs/deuts/movetoland.html

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