Meeting Abstract
Compared to their temperate and tropical relatives, polar marine taxa often reach unusually large body sizes. This phenomenon, known as polar gigantism may be explained by the oxygen hypothesis of Chapelle & Peck (1999, Nature), which states that, in polar conditions, high oxygen availability and low metabolic rates allow larger body sizes. We tested the oxygen hypothesis using sea spiders (pycnogonids), which are small-bodied in temperate regions but reach enormous sizes in polar regions and at great depths. Using temperate and Antarctic species (n = 14 species, varying from 2 mg to 12 g wet weight), we measured the scaling relationships of key aspects of oxygen consumption and transport, including metabolic rate, cuticular conductance, levels of oxygen in the blood, and rates of internal circulation. To integrate these data, we developed a mathematical model describing the radial transport of oxygen from the environment into the tissues. The model accurately predicted the observed concentrations of internal oxygen, which was significantly lower in the largest-bodied Antarctic species > 1 g). Using the established scaling relationships to project the model out to still larger body sizes, we showed that even modestly larger individuals would not obtain sufficient oxygen in the Antarctic, demonstrating that the largest Antarctic taxa are approaching an oxygen-based limit to body size. Additional model simulations suggest even smaller maximum sides at warmer temperatures, which may explain the observed global gradients in pycnogonid body size. NSF PLR-1341485.
