Meeting Abstract
‘Polar gigantism’ describes a biogeographic pattern in which ectotherms in polar seas tend to have larger body sizes than do their warmer-water relatives. Although polar gigantism has been ascribed to a variety of mechanisms, one idea—the oxygen-temperature hypothesis—has received significant attention in the past twenty years. The idea is that low temperatures in polar seas depress metabolic demand for oxygen more than they depress supplies of oxygen to and within organisms. This shift, releases polar organisms from oxygen-based constraints on body size. In this talk, we review evidence for and against the hypothesis. Although some data suggest that larger-bodied taxa live closer to an oxygen limit, or that rising temperatures can challenge oxygen delivery systems, other data provide no support. We propose that these findings can be reconciled, in part, by recognizing that the oxygen-temperature hypothesis, in its simplest incarnation, focuses on passive physical transport of oxygen, which implicitly ignores other important processes, including ventilation of respiratory surfaces, internal transport of oxygen, and behavioral choices about positioning within environmental mosaics. Indeed, the oxygen-temperature hypothesis may apply most meaningfully to organisms that are sessile (e.g., nudibranch egg masses, sessile adults) or that have poorly developed physiological and behavioral systems (eggs and embryos). Finally, most tests of the oxygen-temperature hypothesis have involved short-term experiments. Although most complex organisms can mount effective responses to physiological challenges over such time periods, doing so may incur negative energetic consequences that become apparent only over much longer time scales. We therefore advocate a renewed focus on long-term studies of temperature-oxygen interactions.
