|Deer mice (Peromyscus maniculatus) populate much of
the United States at high and low altitudes (Snyder, 1981). This
species is particularly suitable for studies on hypoxic stress because
it inhabits the widest range of altitudes of any North American mammal,
and it has a large degree of genetic variation for hemoglobin (Snyder,
1982). Seemingly these characteristics make deer mice an ideal
species to study the adaptations of animals to altitude.
Image courtesy of Washington Public Health Information Service.
|In a comprehensive study by Snyder et al. it was
demonstrated that a strong correlation exists between blood oxygen
affinity and altitude. Mice at high altitude exhibited the strongest
blood-oxygen affinity, corresponding to a lower P50 value and a
shift in the oxygen dissociation curve to the left (1982). The trend
exhibited by the deer mice is similar to the llama; deer mice have an
increased ability to extract oxygen from low pressure areas.
However, it is critical that the deer mice and llama not shift the oxygen
dissociation curve too far to the left because that would result in an
inability to release oxygen to the tissues.
A generic oxygen dissociation curve graph for deer mice. Deer mice at increased altitudes show a lower P50 value.
|The ability for the llama and deer mice,
adapted to high altitude, to extract a sufficient amount of oxygen is due
to the concentration of DPG. High ratios of DPG to hemoglobin reduce
the blood-oxygen affinity, while low ratios of DPG to hemoglobin
correspond to a high blood-oxygen affinity (Snyder et al.,1982).
Further, Snyder et al. found that the characteristic DPG to hemoglobin
ratios were passed on to progeny despite a change in native
elevation. This finding suggests the adaptation of altering DPG to
hemoglobin ratios is genetic (1981).
A graph of DPG to hemoglobin ratio versus P50 value. The positive linear relationship demonstrates that as DPG increases the affinity of hemoglobin for oxygen decreases. Image adapted from Snyder et al. (1982).
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Last Updated November 28, 1999