Evolution Biochemical and physiological correlates of deer mouse a - chain hemoglobin polymorphisms ( hemoglobin oxygen affinity / high - altitude adaptation / maximum oxygen consumption / cold exposure exercise )

AIBSTRACT The a-hemoglobin chains in adult deer mice are usually encoded by two tightly linked loci. Because of strong linkage disequilibrium, almost all a-globin haplotypes fall into just two classes. The a0co class predominates in highaltitude populations, whereas the aYcl class is generally fixed in low-altitude populations. Here we show that the a-globin genotype has effects at both the biochemical level [on blood oxygen affinity (P50)] and at the level of whole-anmal physiology [on maximum rate of oxygen consumption (V02..O ) during both exercise and cold exposure]. The ac/a'c' genotype mice have the highest P50 values and show the highest Vo2.,,. values at low altitude (340 m) but the lowest VO2, values at high altitude (3800 m). The a0c0/a' c0 mice have the lowest Pso, and show the highest V02max at high altitude but usually have the lowest V021,,X at low altitude. The adc0/lacl heterozygotes have an intermediate P50 and are generally intermediate in Voice: at both altitudes. Since high V02m., is advantageous for aerobic exercise and thermogenesis, the physiological data provide a potential explanation for the correlation of haplotype frequencies with altitude.