Gregory K. Snyder

Respiratory adaptations in diving mammals

This report examines the evidence for the presence of oxygen stores in the lungs, blood and systemic musculature of diving mammals, the modifications in the respiratory functions of blood that may be important in utilizing the lung and blood oxygen stores, and the potential importance of the oxygen stores and the respiratory functions of blood in supporting short-duration, aerobic dives. Increasing oxygen stores by increasing lung volume does not occur in diving mammals. The long-duration diving whales have small lung volumes which results in lung collapse during dives and the seals dive following partial expiration which produces the same effect. The short-duration diving dolphins, porpoises and rodents have lung volumes comparable to terrestrial mammals, dive following inspiration and appear to use the lungs as an oxygen store. Adaptations in the oxygen affinity of the blood parallel the modifications in lung volume. Where the lungs do not represent a potential oxygen store the oxygen affinity is low, maximizing the unloading of oxygen while maintaining a high tissue oxygen tension. Where the lungs do represent an oxygen store, the affinity is high, maximizing the uptake of oxygen from the alveolar space. Increases in the concentration of respiratory pigment in the blood and in muscle are important adaptations in diving mammals. The blood oxygen stores in diving mammals vary from near normal to over three times normal for terrestrial mammals while the muscle oxygen stores vary from near normal to nearly ten times normal. The degree to which the blood and muscle oxygen stores are increased can be equated to the duration of the dive and demands for oxygen; longer duration divers and those with higher metabolic demands have greater oxygen stores than divers that remain submersed for shorter periods or have lower rates of oxygen utilization.

TEMPERATURE ADAPTATIONS IN AMPHIBIANS

Past studies of ecogeographic character variations have failed to provide a quantitative relationship between the character being measured and the environmental parameter which impinges upon that character. We offer an example in amphibians directly relating a character variation, the range of temperature tolerance, and the critical environmental parameter for that character, the environmental temperature variation. In this example, the range of temperature tolerance is closely related to the environmental temperature variations. Where the environmental temperature variation increases so does the range of temperature tolerance. In addition, where environmental temperatures decrease, the capacity to tolerate such temperatures is lost. These data are consistent with the thesis that congeneric and conspecific populations in different habitats have partially independent evolutionary pathways and that where populations have been displaced from a less to a more uniform environment, characters which are no longer maintained by selection pressure are lost.

Effects of hypoxia on tissue capillarity in geese.

Tissue capillarity in the gastrocnemius and myoglobin concentrations in the gastrocnemius and heart were determined for hatchling Canada geese, Branta canadensis, following incubation of the embryos under either normoxic (Po2 = 120 torr) or hypoxic (Po2 = 94 torr) conditions. Similar observations were made on a limited number of hatchling bar-headed geese, Anser indicus, a species native to high altitude. Capillary densities were higher and diffusion distances shorter in the hypoxic Canada geese and the bar-headed geese than in the normoxic Canada geese. The concentrations of myoglobin in the heart and gastrocnemius increased with mass, but not as a function of hypoxia. We conclude that bird embryos respond to hypoxia by increasing capillarity. The increased capillarity is found in species native to high altitude when incubated under conditions of normoxia and can be induced in species native to sea level by exposure to hypoxia during development.

Effects of hypoxia on muscle capillarity in rats

Capillary density, fiber cross-sectional area, capillary/fiber ratio and fiber composition were determined in gastrocnemius and diaphragm muscles of laboratory rats following five weeks at 350 Torr ambient pressure. Growth rates of hypoxic rats were lower than normoxic controls, but the periods of sacrifice were adjusted to achieve similar body masses for the two groups. Hypoxic rats had significantly higher hematocrits and heart masses, characteristic of acclimation to hypoxia. However, capillary/fiber ratios in gastrocnemius and diaphragm were similar for hypoxic and normoxic rats suggesting that hypoxia did not stimulate capillarity in either muscle. In diaphragm, but not gastrocnemius, diffusion distances were significantly shorter in hypoxic rats than in controls. We conclude that the differences in diffusion distances represent an important secondary effect of hypoxia on the diaphragm associated with changes in demands on ventilation in response to low oxygen pressures.

Capillarity and diffusion distances in skeletal muscles in birds.

SummaryTissue capillarity and diffusion distances were determined for red and white skeletal muscles of adult birds ranging in mass from 10.8 to 6200 g. In addition, literature values for capillarity and diffusion distances in skeletal muscles of mammals were incorporated into the data set. Muscle mass was closely coupled to body mass. However, no significant allometric relations were found for any of the other variables measured. Number of capillaries per fiber was not correlated with cross sectional area of individual muscle fibers. Thus, capillary density decreased in a hyperbolic manner against fiber area and diffusion distance decreased in a hyperbolic manner against the number of capillaries per muscle fiber. Red muscles had significantly higher numbers of capillaries per fiber and significantly shorter diffusion distances than did white muscles. The patterns for tissue capillarity and diffusion distances in avian muscle reported here are similar to values reported previously for mammalian muscles. In both taxanomic groups capillarity and diffusion distances are independent of body mass. In addition, diffusion distances are characteristic of capillaries distributed in random arrays through the muscle cross section.

Development and Metabolism during Hypoxia in Embryos of High Altitude Anser indicus versus Sea Level Branta canadensis Geese

The yolk-free body mass, the mass of selected organs, the rates of oxygen consumption, and the air cell gas tensions were measured throughout incubation in embryos of the bar-headed goose, Anser indicus, and the Canada goose, Branta canadensis. The embryo mass for both species increased exponentially with incubation time to a stage just prior to pipping when growth appeared to stop. The rates of oxygen consumption for the embryos paralleled the rate of growth for the first 40%-50% of the increase in embryo mass, followed by a period when the rate of oxygen consumption plateaued at a value of 43.9 ± 0.7 cm³ O₂/h for the embryos of the Canada goose and 39.1 ± 1.7 cm³ O₂/h for the embryos of the bar-headed goose. The oxygen tensions in the air cell decreased with time concomitant with the increase in oxygen consumption to a value of 96.3 ± 2.0 torr for the Canada goose and 88.0 ± 1.0 torr for the bar-headed goose. The lower air cell oxygen tensions in the bar-headed goose reflect a lower eggshell permeability and smaller egg size. When acutely exposed to hypoxic hypoxia, the normoxic embryos of the bar-headed goose were able to maintain rates of oxygen consumption at significantly lower oxygen tensions than were the embryos of the Canada goose. However, the embryos of the Canada goose were able to acclimate to incubation under conditions of hypoxic hypoxia as evidenced by a shift to the left in the oxygen tension necessary to reduce the rate of oxygen consumption.

Effects of hypoxia, hypercapnia, and pH on ventilation rate in Nauphoeta cinerea.

Abstract Injecting 50 μl of a phosphate-buffered Ringers solution with adjusted oxygen pressure (PO 2 ), Carbon dioxide pressure (PCO 2 ) or hydrogen ion concentration (pH) stimulates ventilation in the cockroach, Nauphoeta cinerea . When the pH of the buffered Ringers is held at 7.08, the observed pH of our cockroach haemolymph, neither a reduced PO 2 nor an elevated PCO 2 produced responses that could account for the observed changes in ventilation in insects during exercise or when exposed to elevated ambient CO 2 . Ventilation changes produced by altering the pH of the injected saline are comparable to those observed in active insects and in insects exposed to elevated ambient CO 2 . We show that the effect of an elevated ambient CO 2 on ventilation can be accounted for by changes in haemolymph pH.

Oxygen permeability of the shell and membranes of chicken eggs during development

Oxygen permeability (KO2) was measured through the shell and shell membranes of chicken eggs throughout incubation. Shell KO2 was constant at 1.90 x 10(-6) cm3 O2 STP . sec-1 . cm-2 . Torr-1. Outer shell membrane KO2 was constant at 1.78 x 10(-6) cm3 O2 STP . sec-1 . cm-2 . Torr-1. Inner membrane KO2 increased from 0.11 x 10(-6) cm3 O2 STP . sec-1 . cm-2. Torr-1 to 1.56 x 10(-6) cm3 O2 STP . sec-1 . cm-2 . Torr-1. Calculations of KO2 from oxygen uptake rates and air cell PO2s were in close agreement with direct measurement of KO2. Resistance to oxygen flux was partitioned at each level. The outer membrane added 6% to the resistance of the shell. The inner membrane initially accounted for 88% of the shell/membrane complex resistance, but fell to 12% of the resistance by the end of incubation. The hypothesis is discussed that the increased permeability of the inner membrane is related to the evaporation of water from the membrane surface. The possibility is rejected that the shell membranes may be potential sites for respiratory adaptation to incubation at altitude.

Adaptations in skeletal muscle capillarity following changes in oxygen supply and changes in oxygen demands

SummaryThe effects of changes in oxygen supply and oxygen demands on fiber cross-sectional areas, capillary dersities and capillary to fiber ratios were determined in three skeletal muscles of rat. The muscles examined were the vastus lateralis, soleus, and diaphragm. Reduced oxygen supply was produced by subjecting rats to ambient hypoxia, and increased oxygen demands were produced by subjecting rats to low ambient temperatures or treatment with thyroxin. Capillaries were visualized by injecting fluorescent dyes into the circulation. Muscles were quick frozen at resting lengths to preserve normal fiber geometry and were subsequently sectioned on a cryostat. All of the muscles sampled from animals in the experimental groups had elevated capillary densities. However, capillary to fiber ratios were not increased significantly in any muscle, for any experimental condition. Thus, all of the observed differences in capillarity were due to changes in the intrinsic rate of muscle fiber growth. Further, the relations of capillary density and capillary to fiber ratio to fiber area were the same as those obtained during normal maturation, suggesting that capillary growth is closely linked to the intrinsic rate of fiber growth.

Olfactory sensitivity in the black-billed magpie and in the pigeon

Abstract 1. 1. Changes in respiration frequency were used to evaluate the olfactory sensitivity of the black-billed magpie and the pigeon to ethanethiol, butanethiol, menthol and putrid meat odorants. 2. 2. The threshold concentrations of ethanethiol and butanethiol, but not menthol, were lower in the magpies than in the pigeons. Only the magpies responded to the putrid meat odorant. 3. 3. The greater responsiveness of the magpies to ethanethiol, butanethiol and putrid meat odorants is attributed to the biological relevance which these odors have for them.