Integrative and Comparative Biology Advance Access originally published online on January 6, 2006
Integrative and Comparative Biology 2006 46(1):49-61; doi:10.1093/icb/icj007
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Into thin air: Physiology and evolution of alpine insects
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*Department of Biology Box 351800 University of Washington Seattle, Washington 98195-1800
Department of Integrative Biology, University of California Berkeley, California 94720
Smithsonian Tropical Research Institute P.O. Box 2072, Balboa, Republic of Panama
Correspondence: 1E-mail: dillonm{at}u.washington.edu
Numerous physical parameters that influence insect physiology vary substantially with altitude, including temperature, air density, and oxygen partial pressure. Here, we review existing literature and present new empirical data to better characterize the high-altitude environment, and then consider how this environment affects the physiology and evolution of insects. Using weather balloon data from fifty-three sites across the globe, we estimate a mean altitudinal temperature lapse rate of 6.0 °C/km. We also present empirically determined lapse rates for PO2 and air density. The temperature decline with elevation may substantially compromise insect thermoregulation at high altitude. However, heat-transfer models predict that lower air density at elevation reduces convective heat loss of insects by to a surprisingly large degree. This effect combined with behavioral thermoregulation and the availability of buffered microhabitats make the net thermal consequences of high-altitude residence strongly context-specific. The decline in PO2 with elevation may compromise insect development and physiology, but its effects are difficult to predict without simultaneously considering temperature and air density. Flying insects compensate for low air densities with both short-term responses, such as increased stroke amplitude (but not wingbeat frequency), and with long-term developmental and/or evolutionary increases in wing size relative to body size. Finally, in contrast to predictions based on Bergmann's Rule, a literature survey of thirty-six insect species suggests that those living in colder, higher altitudes do not tend to have larger body sizes.