Leys Sally P, Kahn Amanda S
Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada.
Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039, USA.
Integr Comp Biol. 2018 Oct 1;58(4):666-676. doi: 10.1093/icb/icy051.
The appearance of multicellular animals during the Neoproterozoic Era is thought to have coincided with oxygenation of the oceans; however, we know little about the physiological needs of early animals or about the environment they lived in. Approaches using biomarkers, fossils, and phylogenomics have provided some hints of the types of animals that may have been present during the Neoproterozoic, but extant animals are our best modern links to the theoretical ancestors of animals. Neoproterozoic oceans were low energy habitats, with low oxygen concentrations and sparse food availability for the first animals. We examined tolerance of extant ctenophores and sponges-as representatives of extant lineages of the earliest known metazoan groups-to feeding and oxygen use. A review of respiration rates in species across several phyla suggests that suspension feeders in general have a wide range of metabolic rates, but sponges have some of the highest of invertebrates and ctenophores some of the lowest. Our own studies on the metabolism of two groups of deep water sponges show that sponges have different approaches to deal with the cost of filtration and low food availability. We also confirmed that deep water sponges tolerate periods of hypoxia, but at the cost of filtration, indicating that normal feeding is energetically expensive. Predictions of oxygen levels in the Neoproterozoic suggest the last common ancestor of multicellular animals was unlikely to have filtered like modern sponges. Getting enough food at low oxygen would have been a more important driver of the evolution of early body plans.
新元古代多细胞动物的出现被认为与海洋的氧化作用同时发生；然而，我们对早期动物的生理需求或它们所生活的环境知之甚少。利用生物标志物、化石和系统发育基因组学的方法已经提供了一些关于新元古代可能存在的动物类型的线索，但现存动物是我们与动物理论祖先的最佳现代联系。新元古代海洋是低能量栖息地，氧气浓度低且最早的动物食物供应稀少。我们研究了现存栉水母和海绵（作为已知最早后生动物类群现存谱系的代表）对摄食和氧气利用的耐受性。对几个门的物种呼吸速率进行综述表明，一般来说悬浮取食者具有广泛的代谢率，但海绵具有一些最高的无脊椎动物代谢率，而栉水母具有一些最低代谢率。我们自己对两组深水海绵代谢的研究表明，海绵有不同方法来应对过滤成本和低食物供应。我们还证实深水海绵能够耐受缺氧期，但代价是过滤，这表明正常摄食在能量上是昂贵的。对新元古代氧气水平的预测表明，多细胞动物的最后共同祖先不太可能像现代海绵那样进行过滤。在低氧环境下获取足够食物可能是早期身体结构进化更重要的驱动力。
