HEMOGLOBIN POLYMORPHISMS IN DEER MICE (PEROMYSCUS MANICULATUS): PHYSIOLOGY OF BETA-GLOBIN VARIANTS AND ALPHA-GLOBIN RECOMBINANTS.

Abstract

Wild populations of deer mice (Peromyscus maniculatus) contain hemoglobin polymorphisms at both alpha-globin (Hba, Hbc) and beta-globin (Hbd) loci. Population gene frequencies of beta-globin variants (d0 and d1 haplotypes) are not correlated with altitude, whereas a1 c1 alpha-globin haplotypes are fixed in low-altitude populations, and a0 c0 haplotypes reach near fixation at high altitudes. We examined the effects of alpha- and beta-globin variants on blood oxygen affinity and on aerobic performance, measured as maximum oxygen consumption (V˙O2max). Exercise and cold exposure were used to elicit V˙O2max. Experiments were performed at low (340 m) and high (3,800 m) altitude to include the range of oxygen partial pressures encountered by wild deer mice. Beta-globin variants had little effect on blood oxygen affinity or V˙O2max. Oxygen-dissociation curves from a0 c0 and a1 c1 homozygotes and heterozygotes had similar shapes, but the P50 of a0 c0 homozygotes was significantly lower than that of other genotypes. Mice carrying a1 c1 /a1 c1 genotypes had the highest V˙O2max at low altitude, but mice with a0 c0 /a0 c0 genotypes had the highest V˙O2max at high altitude. Mice carrying rare recombinant alpha-globin haplotypes (a0 c1 ) had lower V˙O2max than nonrecombinant genotypes as a whole but in most cases were not significantly different from nonrecombinant heterozygotes (a0 c0 /a1 c1 ). We conclude that genetic adaptation to different altitudes was important in the evolution of deer mouse alpha-globin polymorphisms and in the maintenance of linkage disequilibrium in the alpha-globin loci but was not a significant factor in the evolution of beta-globin polymorphisms.