Thin Air: A Cyclist's Camp and the Mountain Mice

Breathing High in the Mountains

1Freya Mbatha, a fourteen-year-old cyclist, spent three summer weeks at a junior team training camp in a mountain town about 2,800 m above sea level. The air there is thinner than at her home, which sits only 200 m above sea level, so each breath brings in less oxygen. On her first rides up the long climbs, Freya ran out of breath much sooner than usual. The team doctor, Dr. Leonie Brachmann, measured the hemoglobin in Freya's blood. Hemoglobin is the protein in red blood cells that carries oxygen to the muscles.

2Higher up the valley, at 3,800 m, a university field station studies deer mice. This species lives from near sea level to high mountain slopes. Winter nights at the station often fall below −10 °C, and a mouse stays warm by using oxygen to release energy from its food as body heat. Blood tests show that each deer mouse has one of two forms of hemoglobin. The highland form picks up oxygen more easily from thin air than the lowland form does.

3Station biologist Dr. Santiago Huerta explained how the team knows the hemoglobin form is passed from parents to young. In the lab, mouse pairs were raised and bred at the same low elevation for several generations. Young mice still had the same hemoglobin form as their parents. Moving an adult mouse to a new elevation did not change its form.

4Each October, the team traps adult mice at the high station and at a second station at 400 m. They test a drop of blood from each mouse, put a small tag in its ear and release it where it was caught. In May they trap again to find out which tagged mice survived the winter. Over the summer, they check nest boxes at the high station to count the litters each surviving female raises and the young in each litter.