Woods H Arthur, Moran Amy L, Arango Claudia P, Mullen Lindy, Shields Chris
Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA.
Proc Biol Sci. 2009 Mar 22;276(1659):1069-75. doi: 10.1098/rspb.2008.1489.
Compared to temperate and tropical relatives, some high-latitude marine species are large-bodied, a phenomenon known as polar gigantism. A leading hypothesis on the physiological basis of gigantism posits that, in polar water, high oxygen availability coupled to low metabolic rates relieves constraints on oxygen transport and allows the evolution of large body size. Here, we test the oxygen hypothesis using Antarctic pycnogonids, which have been evolving in very cold conditions (-1.8-0 degrees C) for several million years and contain spectacular examples of gigantism. Pycnogonids from 12 species, spanning three orders of magnitude in body mass, were collected from McMurdo Sound, Antarctica. Individual sea spiders were forced into activity and their performance was measured at different experimental levels of dissolved oxygen (DO). The oxygen hypothesis predicts that, all else being equal, large pycnogonids should perform disproportionately poorly in hypoxia, an outcome that would appear as a statistically significant interaction between body size and oxygen level. In fact, although we found large effects of DO on performance, and substantial interspecific variability in oxygen sensitivity, there was no evidence for sizexDO interactions. These data do not support the oxygen hypothesis of Antarctic pycnogonid gigantism and suggest that explanations must be sought in other ecological or evolutionary processes.
与温带和热带的同类物种相比，一些高纬度海洋物种体型巨大，这一现象被称为极地巨大症。关于巨大症生理基础的一个主要假说是，在极地水域，高氧可用性与低代谢率相结合，减轻了对氧气运输的限制，从而使得大型体型得以进化。在此，我们利用南极海蜘蛛来检验这一氧气假说，南极海蜘蛛已经在非常寒冷的条件（-1.8至0摄氏度）下进化了数百万年，其中包含了巨大症的惊人实例。从南极洲麦克默多湾采集了12个物种的海蜘蛛，它们的体重跨越了三个数量级。将单个海蜘蛛逼使其活动，并在不同的溶解氧（DO）实验水平下测量它们的表现。氧气假说预测，在其他条件相同的情况下，大型海蜘蛛在低氧环境中的表现应该会不成比例地差，这一结果将表现为体型大小与氧气水平之间具有统计学意义的相互作用。事实上，尽管我们发现溶解氧对表现有很大影响，并且在氧气敏感性方面存在显著的种间差异，但没有证据表明存在体型大小与溶解氧的相互作用。这些数据不支持南极海蜘蛛巨大症的氧气假说，并表明必须在其他生态或进化过程中寻找解释。
