1 Department of Biology, University of Hawai'i at Mānoa , Honolulu, HI 96822 , USA.
2 Division of Biological Sciences, University of Montana , Missoula, MT 59812 , USA.
Proc Biol Sci. 2019 Apr 10;286(1900):20190124. doi: 10.1098/rspb.2019.0124.
The extreme and constant cold of the Southern Ocean has led to many unusual features of the Antarctic fauna. One of these, polar gigantism, is thought to have arisen from a combination of cold-driven low metabolic rates and high oxygen availability in the polar oceans (the 'oxygen-temperature hypothesis'). If the oxygen-temperature hypothesis indeed underlies polar gigantism, then polar giants may be particularly susceptible to warming temperatures. We tested the effects of temperature on performance using two genera of giant Antarctic sea spiders (Pycnogonida), Colossendeis and Ammothea, across a range of body sizes. We tested performance at four temperatures spanning ambient (-1.8°C) to 9°C. Individuals from both genera were highly sensitive to elevated temperature, but we found no evidence that large-bodied pycnogonids were more affected by elevated temperatures than small individuals; thus, these results do not support the predictions of the oxygen-temperature hypothesis. When we compared two species, Colossendeis megalonyx and Ammothea glacialis, C. megalonyx maintained performance at considerably higher temperatures. Analysis of the cuticle showed that as body size increases, porosity increases as well, especially in C. megalonyx, which may compensate for the increasing metabolic demand and longer diffusion distances of larger animals by facilitating diffusive oxygen supply.
南大洋极端且持续的寒冷导致了南极动物群的许多不寻常特征。其中之一是极地巨型化，据认为这是由寒冷驱动的低代谢率和极地海洋中高氧气含量的结合（“氧气-温度假说”）所致。如果氧气-温度假说确实是极地巨型化的基础，那么极地巨兽可能特别容易受到温度升高的影响。我们使用两种巨型南极海蜘蛛（Pycnogonida）属 Colossendeis 和 Ammothea，在一系列体型范围内，通过测试温度对性能的影响来检验这一假说。我们在四个温度下测试了性能，范围从环境温度（-1.8°C）到 9°C。两个属的个体对高温都非常敏感，但我们没有发现证据表明大型 Pycnogonida 比小个体更容易受到高温的影响；因此，这些结果并不支持氧气-温度假说的预测。当我们比较两种物种，即 Colossendeis megalonyx 和 Ammothea glacialis 时，C. megalonyx 在更高的温度下保持了性能。对表皮的分析表明，随着体型的增大，多孔性也会增加，尤其是在 C. megalonyx 中，这可能通过促进扩散氧气供应来补偿较大动物不断增加的代谢需求和更长的扩散距离。
