TITLE:
Origin and development of homoiothermy: A case study of avian energetics
AUTHORS:
Valery M. Gavrilov
KEYWORDS:
Basal Metabolism; Metabolism of Existence; Homoiothermy; Erythrocytes in Birds and Mammals; Aerobic Supply of Activity and Sensory Systems; Minimal Size; Parental Care
JOURNAL NAME:
Advances in Bioscience and Biotechnology,
Vol.4 No.8A,
August
8,
2013
ABSTRACT: The
study is based on the results of the integrated measurement of the energy
expenditure at rest and common activity in birds belonging to various systematic
groups. Homeothermy has formed in birds and mammals independently and in
different geological ages. However, in both groups it originated as a side
effect of selection for aerobic metabolism improvement that provided a higher
level of activity. Advantages of having high and stable body temperature,
which were inevitably related with metabolism intensification, led to
development of thermoregulatory adaptations such as fur and feathers. This
made it possible to retain the metabolically generated heat and reduce heat
absorption in hot environments. Emergence of homeothermy with aerobic supply of
motion activity, possibilities to regulate the level of metabolism and thermal
conductance, has opened a lot of opportunities for homoeothermic animals. Achieving such a level of energy utilization allowed them to maintain activity for
a longer time, while its sensory support led to complication and diversification
of birds’ behavioral repertoire (as well as that of mammals) facilitating the
conquest of almost entire part of the biosphere that was suitable for living.
This process was favored by the development of nurturing and passing on the
information, collected throughout the life, to new generations. Formation of
high levels of aerobic metabolism in birds and mammals was proceeding in
parallel among different groups of reptilian ancestors. The level of homeothermy,
at which aerobic metabolism was able to maintain prolonged activity, developed
in birds and mammals in different ways: they had got dissimilar partitioning of
venous and arterial networks, erythrocytes with or without a cell nucleus,
different lungs design—but, at that, similar minimum
metabolic power and rather close body temperatures which corresponded
well to the environmental conditions on the Earth.
Natural selection allowed animals with high energetic metabolism to increase
their diversity and abundance, but only when homoeothermic animals could
satisfy their demands for food resources, that had risen manifold. That
happened in the middle of Cretaceous, in time with the appearance of
angiosperms and expansion of related fauna of invertebrates.