Dive Performance and Aquatic Thermoregulation of the World’s Smallest Mammalian Diver, the American Water Shrew (Sorex palustris)

Abstract

Jones (1997) formulated the adaptive hypothermia hypothesis to explain why some species routinely exceed their oADL. By intentionally decreasing core T6, divers can theoretically decrease DMR, due to the Q¡6 effect, and thereby extend dive duration while maintaining an aerobic metabolism (Geiser 1988).However, the benefit of increased aerobic dive endurance comes with the mandatory energetic cost of re-warming cooled tissues after immersion. Studies examining the "adaptive hypothermia" argument have yielded mixed results (Hall et al. 1987, Ponganis et a|.2003, Hindle et a|.2006). The water shrew offers an ideal model for testing this hypothesis. This is because it has the largest surface-area-to-volume ratio, smallest onboard Oz stores and the highest mass-specific diving metabolic rate of any diver, all factors that predict rapid cooling and a limited scope for dive endurance.