Maintaining adequate internal water concentrations is done by a variety of mechanisms which are highly variable depending upon the organism. These mechanisms appear to have evolved to suit the organism to the specific environment in which it lives. If the organism is removed from this environment, water loss or gain may be extremely detrimental.

This study utilized two animals, the California Newt (Taricha torosa) and the Fence Lizard (Sceloporus occidentalis) in an attempt to better understand the effects of osmotic change due to environments. T. torosa is a semi-terrestrial amphibian, and like all amphibians, respires through the integument. In a fresh water aquatic environment, this is advantageous for oxygen uptake as well as for maintaning an adequate internal fluid osmolarity. In the terrestrial envir

In the wet environments in which excess water was available, the mass of the organism was kept relatively stable (Fig 1.1, 1.4, 1.5). This process is controlled primarily by uptake of water through the integument and removal by large quantities of dilute urine.

By utilizing various mechanisms, T. torosa is able to osmoregulate, or control

A primary characteristic of the amphibians is the presence of an integument

In times of dehydration, most amphibians do not urinate or defecate (Feder and Burggren 1992). Additionally, newts are able to conserve water by means of nervous and hormonal control. In the presence of water loss nearing that of dehydration, the hormone arginine vasotocin (AVT) is released from the neurohypophysis. This hormone is believed to regulate the water permeability of the bladder and the skin as well as participate in regulating kidney urine production (Feder and Burggren 1992). Because amphibians are able to store up to 50% of their mass in body water in the bladder, extracting this water in the presence of AVT would be beneficial in sustaining adequate osmotic concentrations. By looking at the results of this experiment, a gradual decline in the rate of weight loss may be noted following the first hour of the experiment in dry conditions (Figure 1.1, 1.4, 1.5). AVT is also thought to act on the kidneys by reducing the glomerular filtration rate (GFR). In previous experiments, AVT injection reduced the GFR by 84% (Brown and Brown 1980) In the presence of dehydrating condtions, most amphibians become anuric within 8 to 10 hours (Feder and Burggren 1992). If these processes are indeed occurring, they are hard to determine and are quantitatively beyond the scope of this study.

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