Genetic Differences in Physiological Tolerances of Amargosa Pupfish ( Cyprinodon nevadensis ) Populations

Amargosa pupfish from a constant-temperature spring have a narrower range of temperature and oxygen tolerances than pupfish from the much more variable Amargosa River, indicating that the two populations have diverged genetically since their isolation. The reduced tolerances of the fish inhabiting a constant environment support the predictions of evolution theory.