Brocks Jochen J
Research School of Earth Sciences, The Australian National University, Canberra, Australian Capital Territory 2601, Australia.
Emerg Top Life Sci. 2018 Sep 28;2(2):181-190. doi: 10.1042/ETLS20180039.
The Neoproterozoic, 1000-541 million years (Myr) ago, saw the transition from a largely bacterial world to the emergence of multicellular grazers, suspension feeders and predators. This article explores the hypothesis that the first appearance of large, multicellular heterotrophs was fueled by an elevated supply of nutrients and carbon from the bottom of the food chain to higher trophic levels. A refined record of molecular fossils of algal sterols reveals that the transition from dominantly bacterial to eukaryotic primary production in open marine habitat occurred between 659 and 645 Myr ago, in the hot interlude between two Snowball Earth glaciations. This bacterial-eukaryotic transition reveals three characteristics: it was rapid on geological timescales, it followed an extreme environmental catastrophe and it was permanent - hallmarks of an ecological hysteresis that shifted Earth's oceans between two self-stabilizing steady states. More than 50 million years of Snowball glaciations and their hot aftermath may have purged old-world bacterial phytoplankton, providing empty but nutrient-rich ecospace for recolonization by larger algae and transforming the base of the food web. Elevated average and maximum particle sizes at the base of the food chain may have provided more efficient energy and nutrient transfer to higher trophic levels, fueling an arms race toward larger grazers, predators and prey, and the development of increasingly complex feeding and defense strategies.
新元古代，即10亿至5.41亿年前，见证了从以细菌为主的世界向多细胞食草动物、悬浮取食者和捕食者出现的转变。本文探讨了一种假说，即大型多细胞异养生物的首次出现是由从食物链底层到更高营养级的营养物质和碳供应增加所推动的。一份经过完善的藻类固醇分子化石记录显示，开阔海洋栖息地从以细菌为主导的初级生产向真核生物初级生产的转变发生在6.59亿至6.45亿年前，处于两次雪球地球冰川期之间的温暖间隔期。这种细菌向真核生物的转变呈现出三个特征：在地质时间尺度上很迅速，它发生在一场极端环境灾难之后，而且是永久性的——这些都是生态滞后的标志，这种滞后使地球海洋在两种自我稳定的稳态之间转换。超过5000万年的雪球冰川期及其之后的温暖时期可能清除了旧世界的细菌浮游植物，为大型藻类的重新定殖提供了空旷但营养丰富的生态空间，并改变了食物网的基础。食物链底层平均粒径和最大粒径的增加可能为向更高营养级更有效地传递能量和营养物质，推动了朝着更大的食草动物、捕食者和猎物发展的军备竞赛，以及日益复杂的摄食和防御策略的发展。
