Is Heterothermy in Endotherms an Evolutionary Primitive Feature - Term Paper Example

There are arguments that heterothermic animals are actually primitive phylogenetically and there have been past arguments that heterothermy is an evolutionary stage between ectothermy and homeothermic.  A contradicting view suggests that heterothermy is polyphylectic and indicates how an animal adapts to the environment. This has led to a lack of agreement on the right argument to describe heterothermy (Zotin, 1990). Thus, it has been necessary to assess each argument and come up with a conclusion regarding the argument that appears to explain heterothermy conditions in some mammals, birds, and marsupials. In addition, most biologists have usually referred to mammals and birds as homeotherms despite the observation that these animals experience temporal changes in body temperature. These variations have been associated with adaptive strategies of heterothermy that are favorable for genotypes of various ranges. The coadaptation process has been done in ectoderms but the focus has not been put on endotherms that experience similar conditions. Thus classical models have been developed in this paper that assist in prediction in body temperature among birds and mammals populations.

The evolution of hibernation and diurnal torpor among mammals and birds has also been a subject of concern. Originally it was viewed that torpor was an indication of primitive thermoregulation due to its occurrence in ancestral groups of mammals (Willmer, Stone & Johnston, 2005). This view has been disregarded but the interpretation of a polyphyletic derivation of torpor has not been accepted fully due to the similarity patterns among a number of orders. Despite hibernation occurring in mammals in the phylogenetically old groups, thus supporting the idea of an ancestral origin of torpor, the opposite has been observed in birds. Modern groups of birds contain generally small species that are dependent on fluctuating supply of food, while modern mammalian orders and other birds contain large species that require a low amount of energy for maintenance and thermoregulation (Wang & Boulant, 1989).