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Annual Review of Physiology papers



Something from beyond the Florida debacle [abstracts follow]....

Dudley, R. 2000. The Evolutionary Physiology of Animal Flight:
Paleobiological and Present Perspectives. Annual Review of Physiology
62: 135-155.

  Recent geophysical analyses suggest the presence of a late Paleozoic
oxygen pulse beginning in the late Devonian and continuing through to
the late Carboniferous. During this period, plant terrestrialization
and global carbon deposition resulted in a dramatic increase in
atmospheric oxygen levels, ultimately yielding concentrations
potentially as high as 35% relative to the contemporary value of 21%.
Such hyperoxia of the late Paleozoic atmosphere may have
physiologically facilitated the initial evolution of insect flight
metabolism. Widespread gigantism in late Paleozoic insects and other
arthropods is also consistent with enhanced oxygen flux within
diffusion-limited tracheal systems. Because total atmospheric pressure
increases with increased oxygen partial
pressure, concurrently hyperdense conditions would have augmented
aerodynamic force production in early forms of flying insects. By the
late Permian, evolution of decompositional microbial and fungal
communities, together with disequilibrium in rates of carbon
deposition, gradually reduced oxygen concentrations to values possibly
as low as 15%. The disappearance of giant insects by the end of the
Permian is consistent with extinction of these taxa for reasons of
asphyxiation on a geological time scale. As with winged insects, the
multiple historical origins of vertebrate flight in the late Jurassic
and Cretaceous correlate temporally with periods of elevated
atmospheric oxygen. Much discussion of flight performance in
Archaeopteryx assumes a contemporary atmospheric composition. Elevated
oxygen levels in the mid- to late Mesozoic would, however, have
facilitated aerodynamic force production and enhanced muscle power
output for ancestral birds, as well as for precursors to bats and
pterosaurs.

Also, perhaps overlooked, but relevant:

Farmer, C.G. 1999. Evolution of the Vertebrate Cardio-Pulmonary System.
Annual Review of Physiology 61: 573-592.

  Vertebrate lungs have long been thought to have evolved in fishes
largely as an adaptation for life in hypoxic water. This view overlooks
the possibility that lungs may have functioned to supply the heart with
oxygen and may continue to serve this function in extant fishes. The
myocardium of most vertebrates is avascular and obtains oxygen from
luminal blood. Because oxygen-richpulmonary blood  mixes with
oxygen-poor systemic blood before entering the heart of air-breathing
fishes, lung ventilation may supply the myocardium with oxygen and
expand aerobic exercise capabilities. Although sustained exercise in
tetrapods is facilitated by septation of the heart and the formation of
a dual pressure system, a divided cardio-pulmonary system may conflict
with myocardial oxygenation because the right side of the heart is
isolated from pulmonary oxygen. This may have contributed to the
evolution of the coronary circulation.

Harrison, J.F. and Roberts, S.P. 2000. Flight Respiration and
Energetics. Annual Review of Physiology 62: 179-205.

  We use a comparative approach to examine some of the physiological
traits that make flight possible. Comparisons of related fliers and
runners suggest that fliers generally have higher aerobic metabolic
capacities than runners but that the difference is highly dependent on
the taxa studied. The high metabolic rates of fliers relative to
runners, especially in insects, are correlated with high locomotory
muscle cycle frequencies and low efficiences of conversion of metabolic
power to mechanical power. We examine some factors that produce
variation in flight respiration and energetics. Air temperature
strongly affects the flight metabolic rate of some insects and birds.
Flight speed interacts with flier mass, so that small fliers tend to
exhibit a J-shaped power curve and larger fliers a U-shaped power
curve. As body size increases, mass-specific aerobic flight metabolism
decreases in most studies, but mass-specific power output is constant
or increases, leading to an increase in efficiency with size.
Intraspecific studies have revealed specific genetically based effects
on flight metabolism and power output and multiple ecological
correlates of flight capabilities.

=====
Jaime "James" A. Headden

  Dinosaurs are horrible, terrible creatures! Even the
  fluffy ones, the snuggle-up-at-night-with ones. You think
  they're fun and sweet, but watch out for that stray tail
  spike! Down, gaston, down, boy! No, not on top of Momma!

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