Oxygen, temperature and the deep-marine stenothermal cradle of Ediacaran evolution
Oxygen, temperature and the deep-marine stenothermal cradle of Ediacaran evolution
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DOI：
10.1098/rspb.2018.1724
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发表时间：
2018-12-01
影响因子：
4.7
通讯作者：
Sperling, Erik A.
中科院分区：
文献类型：
--
作者：
Boag, Thomas H.;Stockey, Richard G.;Sperling, Erik A.
埃迪卡拉纪化石记录了复杂的巨型生命的早期演化，与广泛的海洋缺氧的地球化学证据同期。这些数据表明，早期动物经历了频繁的缺氧。因此，研究的重点是早期动物所需的分子氧(O-2)浓度，同时也考虑了气候的影响。一种名为冷摇篮假说的模型认为，埃迪卡拉纪生物群起源于寒冷的浅水环境，原因是O-2的溶解度增加。首先，我们利用气体交换原理证明，温度在控制O-2的生物利用率方面确实起着关键作用--但在较凉爽的水中，O-2的供应量实际上较低。其次，化石记录表明，埃迪卡拉生物群最初出现在深水相约571 Ma，然后出现在陆架环境约555 Ma。我们提出了这种模式的生态生理学基础。通过结合海洋资料和新的呼吸测量实验，我们发现在季节温度波动较大的浅混合层中，温度和分压(Po(2))的影响是高度协同的。结果是，远离物种特有的最适温度的变化削弱了对低Po(2)的耐受性。我们假设，埃迪卡拉海的深部和特别狭窄的(狭窄温度范围)环境是躲避温度和低Po(2)协同作用的生理避难所。
Ediacaran fossils document the early evolution of complex megascopic life, contemporaneous with geochemical evidence for widespread marine anoxia. These data suggest early animals experienced frequent hypoxia. Research has thus focused on the concentration of molecular oxygen (O-2) required by early animals, while also considering the impacts of climate. One model, the Cold Cradle hypothesis, proposed the Ediacaran biota originated in cold, shallow-water environments owing to increased O-2 solubility. First, we demonstrate using principles of gas exchange that temperature does have a critical role in governing the bioavailability of O-2-but in cooler water the supply of O-2 is actually lower. Second, the fossil record suggests the Ediacara biota initially occur approximately 571 Ma in deep-water facies, before appearing in shelf environments approximately 555 Ma. We propose an ecophysiological underpinning for this pattern. By combining oceanographic data with new respirometry experiments we show that in the shallow mixed layer where seasonal temperatures fluctuate widely, thermal and partial pressure (pO(2)) effects are highly synergistic. The result is that temperature change away from species-specific optima impairs tolerance to low pO(2). We hypothesize that deep and particularly stenothermal (narrow temperature range) environments in the Ediacaran ocean were a physiological refuge from the synergistic effects of temperature and low pO(2).