Abstract
The use of regulatory and obligatory heat production mechanisms were
studied in
juvenile birds during the development of endothermy.
The development of shivering thermogenesis was studied in the pectoral and
gastrocnemius muscles of the altricial domestic pigeon and in three precocial
galliforms (Japanese quail, grey partridge and domestic fowl). The development of
shivering was the determinant for the beginning of endothermy. Homeothermy also
necessitated avoidance of excess heat loss by insulation and behavioural
thermoregulation. In the precocial species, shivering thermogenesis was present
in the leg muscles of the youngest age groups (1-2 d) studied. Breast muscles
contributed shivering from the second post-hatching week. In the altricial
pigeons, significant thermogenesis was apparent later than in the precocials, at
the age of 6 d. In contrast to the precocials, the pectoral muscles of the
altricials were the most significant heat production tissues. In newly-hatched
partridges and pigeons, incipient shivering did not result in significant heat
production.
The ability to produce heat in cold by putative nonshivering thermogenesis
was
studied in Japanese quail chicks and domestic ducklings. In both species,
three-week cold acclimation resulted in morphometric and physiological changes,
but there was no clear evidence of nonshivering thermogenesis. The lack of NST
was evident because an increase in shivering amplitude at least in one of the
muscles studied paralleled an increase in oxygen consumption. Consequently,
shivering thermogenesis was probably the only mode of regulatory heat
production.
The amplitudes of shivering EMGs measured during cold exposure were
dependent on
the coexistence of postprandial thermogenesis or exercise. Japanese quail chicks
were able to substitute shivering thermogenesis partially with postprandial heat
production when nourished. Bipedal exercise both inhibited shivering in pectorals
directly via inhibitory neural circuits and stimulated it indirectly via
decreased body temperature. Because of increased heat loss, exercise was not used
as a substitute for shivering.
Shivering is a flexible mode of thermogenesis and its magnitude can be
adjusted
according to the magnitude of obligatory thermogenesis. The adjustment works
towards energy saving by avoidance of the summation of different modes of heat
production. The prerequisite for successful adjustment of shivering is adequate
insulation, whose role in preventing excessive heat loss is pronounced during
exercise. It is concluded that the energetics of posthatching thermoregulation
includes the potential for optimizations in energy use in order to avoid
dissipation of waste energy as heat.
| Identifer | oai:union.ndltd.org:oulo.fi/oai:oulu.fi:isbn951-42-6542-4 |
| Date | 30 October 2001 |
| Creators | Marjoniemi, K. (Kyösti) |
| Publisher | University of Oulu |
| Source Sets | University of Oulu |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess, © University of Oulu, 2001 |
| Relation | info:eu-repo/semantics/altIdentifier/pissn/0355-3191, info:eu-repo/semantics/altIdentifier/eissn/1796-220X |
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