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The Journal of Experimental Biology 204, 1991-2000 (2001)
© 2001 The Company of Biologists Limited

Effects of Altitude and Temperature on Organ Phenotypic Plasticity Along an Altitudinal Gradient

Kimberly A. Hammond^1,2,*, Joe Szewczak² and Elbieta Król^1,3

¹ Department of Biology, University of California, Riverside, CA 92521, USA,
² University of California White Mountain Research Station, 3000 East Line Street, Bishop, CA 93514, USA
³ Department of Zoology, University of Aberdeen, Aberdeen AB24 2TZ, Scotland, UK

*e-mail: khammond{at}ucrac1.ucr.edu

Accepted March 13, 2001

Small mammals living in high-altitude environments must endure decreased ambient temperatures and hypoxic conditions relative to sea-level environments. Previously, it was noted that heart, lung and digestive tract masses and blood hematocrit increase along an altitudinal gradient in small mammals. Increases in digestive organ mass were attributed to lower ambient temperatures and greater food intake, and increases in lung mass and hematocrit were attributed to hypoxia, but these assumptions were not explicitly tested. In addition, it was not clear whether changes in heart and lung mass were a function of an increase in organ blood content or of an increase in organ tissue mass. We used captive deer mice (Peromyscus maniculatus sonoriensis) to determine the relative effects of ambient temperature and oxygen concentration (P_O2) on organ mass and blood hematocrit along an altitudinal gradient. We also exsanguinated hearts and lungs to determine whether changes in mass were associated with the blood content or with increases in tissue mass. We found that small intestine mass was, as expected, correlated positively with energy intake and negatively with ambient temperature. Heart mass was also negatively correlated with temperature. Lung mass and hematocrit were, as expected, positively correlated with altitude (and P_O2). Interestingly, the masses of both small intestine and kidney were negatively correlated with altitude. For kidney mass, this correlation was apparent in cold-exposed mice but not in warm-exposed mice. We also found that changes in both heart and lung mass were mainly a function of changes in tissue mass rather than blood content. These data show that different abiotic variables have different effects on organ masses at high altitude, but also that phenotypic plasticity in response to cold temperatures and low oxygen pressures at altitude is widespread across several different organ systems, suggesting a general elevated whole-body response.

Key words: deer mouse, Peromyscus maniculatus sonoriensis, phenotypic plasticity, lung mass, heart mass, small intestine mass, altitude, temperature, hypoxia

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