Ectotherms

An endothermic animal generates its own body temperature, while an ectothermic animal does not. In general, endothermic animals have constant body temperatures that are typically greater than that of the surrounding environment, while ectothermic animals have variable temperatures. Ectotherms rely on behavioral temperature regulation—a snake will move from sun to shade until it finds a suitable microclimate that is close to its optimal body temperature. When exposed to direct sunlight, an ectotherm can increase its body temperature as much as 1°C (32.8°F) per minute. 

Endothermic animals can achieve and sustain levels of activity even when temperatures plummet or vary widely. This can be a huge advantage over ectothermy, especially m northern latitudes, at night, or during the winter. In colder climates, an ectothermic predator such as a snake will tend to be more sluggish and less successful than an endothermic predator. There are no reptiles or insects in the polar regions. 

Figure 32.8 Relation between diet, metabolism, and body weight with half-time retention of longest-lived component of cesium-137. Data are shown for selected ruminant and nonruminant mammals (Richmond 1989) and ectotherms (Hinton and Scott 1990.)... 

Another example is the interdisciplinary laboratory developed at Harvey Mudd College (147) in which eight different interdisciplinary experiments, ranging from thermal properties of an ectothermic animal to synthesis and characterization of liquid crystals, are carried out over two semesters. 

Clarke, A. (1985). The physiological ecology of polar marine ectotherms energy budget, resource allocation and low temperature. Oceanis 11,11-26. 

Lewis, R.W. (1962). Temperature and pressure effects on the fatty acids of some marine ectotherms. Comparative Biochemistry and Physiology 6,75-89. 

Parry, G.D. (1983). The influence of the cost of growth on ectotherm metabolism. Journal ofTheoretical Biology 101,453-477. 

Herbivores in the sea are phylogenetically more diverse than on land. Seaweeds are eaten by diverse vertebrate ectotherms and an array of invertebrate consumers that vary both in their selectivity and in their impact on algae. Vertebrate herbivores are comprised of various fish families and species, as well as some turtles.24 111 120 125 Invertebrate herbivores span at least four different phyla and include an array of gastropods (such as snails, limpets, sacoglossans, sea hares, cephalaspideans, and chitons), urchins, crabs, amphipods, isopods, shrimps, polychaete worms, copepods, and a few insect species that feed on algae living in the upper littoral zone.24 110 123 126-135... 

Schistocephalus solidus has its plerocercoid stage in an ectotherm (the fish Gasterosteus aculeatus) and its adult stage in an endoderm (a fish-eating bird) and it serves as an excellent model for the study of temperature adaptation in parasites. Walker Barrett (922,923) have studied the effect of temperature on (a) the activities of the mitochondrial enzyme adenosine triphosphatase (ATPase) and (b) the physical state of mitochondrial membranes in adult and larval S. solidus. 

Theoretically, if the plerocercoid behaves similarly to a typical ectotherm, it would be expected to possess biological mechanisms which would enable the plerocercoid (whilst within the fish host) to cope with variations... 

Interestingly, in addition to mitochondrial membrane differences, the properties of the plasma membranes in ectotherms compared to endotherms show similar differences in degrees of unsaturation of the phospholipid constituents. The higher proportion of polyunsaturated fatty acyl chains in endotherms in turn correlates with three- to four-fold higher Na+ and K+ background conductance and hence-higher... 

Na+ pump (or Na+-K+-ATPase) activities in endotherms than in ectotherms (see Flulbert and Else, 2000). 

Brookes, P.S., J.A. Buckingham, A.M. Tenreiro, A.J. Hulbert, and M.D. Brand (1998). The proton permeability of the inner membrane of liver mitochondria from ectothermic and endothermic vertebrates and from obese rats correlations... 

There is a large and somewhat contentious literature dealing with the question of how fully the respiratory rates of ectotherms can be adjusted to offset g10 effects on metabolic reactions, a process known as temperature compensation of metabolism. Metabolic compensation... 

In summary, a common set of thermodynamic rules governing protein folding applies across the full spectrum of temperatures permissive of life, and it is the line-tuning of protein sequences using these rules that allows cells as different as those of Antarctic ectotherms and hot-spring archaea to conduct many of the same types of enzymatic processes at temperatures that differ by up to 115°C. 

Cold stress may induce synthesis of heat-shock (stress) proteins. Exposure of cells to cold shock may lead to the induction of one or more of the classes of molecular chaperones that also are induced by heat shock. This is strong evidence that low temperature, like high temperature, can lead to non-native protein structures in vivo and, therefore, to the requirement for enhanced chaperoning activity. Induction of cold-induced protein chaperones has been seen in bacteria (Salotra et al., 1995), in whole organism studies of ectothermic animals (Petersen et al., 1990 Yocum et ah, 1991),... 

In addition to these challenging physical constraints, the demands for food that an endothermic homeotherm faces are substantially greater than those for an ectotherm of the same body mass. At the same body temperature, on a unit mass basis, similar-sized endotherms and ectotherms differ in oxygen consumption on average by at least four- to fivefold (see Brand et al., 1991). It is obvious that many ectother-mic species may not have access to enough food, at all times, to make it possible, even in principle, for them to become endothermic homeotherms. An ecosystem in which all animals are endothermic homeotherms is probably impossible. 

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