Poikilotherms

Poikilotherms are organisms in which their body temperature is directly proportional to their surrounding environments temperature. Most fish and sub tidal marine invertebrates can be described as poikilotherms.

These organisms can achieve an intermediate status, this is when an organism's body temperature is higher than the surroundings temperature. Intermediate status can be achieved by increasing their metabolic rate thus increasing temperature. For example strong swimming fish such as Yellowfin Tuna. (Tait, R.V 1981)

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In contrast some poikilotherms can maintain themselves at temperatures lower then their surroundings, this can be achieved by circulation of body fluids. These intertidal organisms are adpated to have dark complexions in order for them to absorb more heat from the sun. The variations in these organisms can be used to determine the latitude from which the organism inhabits. (Levinton,J 2001)

Poikilotherms can change the speed of their metabolic rate in order to survive a sudden change in temperature of their surroundings. Tropical crabs for example can decrease their metabolic rate when exposed to cold temperatures that they are not used to in their hot climates.

In addition at low temperatures most poikilotherms can increase their oxygen consumption. The oxygen consumption of the same species can be higher in organisms of high latitudes compared to those at low latitudes these differences can be described as Physiological races.

The biochemical aspects of a poikilotherm can also be adapted to survive in cold temperatures of the ocean. For example the sea mussel Mytilus Californianus can cause the phospholipids within its membranes to become more closely packed together, this causes the membrane structure to become more ordered limiting the amount of transport across the membranes. Limiting the amount of transport between cells alters the metabolism of an organism and can cause a reduction in the metabolic rate of an organism.

Some poikilotherms are naturally adapted to survive in very cold temperatures within the ocean. In some Arctic species such as Trematomus bernacchii can conduct ATP synthesis at the lowest of any other marine species in order to adapt to the lowest of temperatures within the Arctic. (Levinton, J 2001)

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Homeotherms are organisms that behave differently to poikilotherms to find out more click the link below.