Amphipod gigantism dictated by oxygen availability?

<jats:p>A recent study of gigantism in amphipods proposes a novel mechanism which could be used to explain Bergmann’s rule, namely differences in environmental O<jats:sub>2</jats:sub> concentration. Consideration of the respiratory biology of this group indicates significant flaws in this proposal. Nonetheless, it is not unreasonable to predict a relationship between ectotherm body size and O<jats:sub>2</jats:sub> partial pressure (<jats:italic>p</jats:italic>O<jats:sub>2</jats:sub>) in some systems, where the partial pressure gradient is steep, either in time (comparison of Carboniferous and Permian atmospheres) or space (animals inhabiting oceanic O<jats:sub>2</jats:sub> minimum layers, and, particularly in freshwaters, living at high altitude). Animal gigantism can be correlated with periods of very high environmental <jats:italic>p</jats:italic>O<jats:sub>2</jats:sub> over geological time. Unfortunately, data for present day spatial patterns are scant.</jats:p>