Radiolarians decreased silicification as an evolutionary response to reduced Cenozoic ocean silica availability
Radiolarians decreased silicification as an evolutionary response to reduced Cenozoic ocean silica availability
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放射虫减少硅化是对新生代海洋二氧化硅可用性减少的进化反应
DOI：
10.1073/pnas.0812979106
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
D. Schmidt
中科院分区：
文献类型：
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作者：
D. Lazarus;Benjamin Kotrc;G. Wulf;D. Schmidt
据推测，水柱分层的增加是影响新生代海洋浮游生物平均细胞大小的非生物“普遍驱动因素”。相比之下，新生代放射虫壳重量的逐渐减少表明，对溶解的二氧化硅（一种共享营养物质）的竞争导致了放射虫和海洋硅藻之间的生物协同进化，这种进化在新生代急剧扩大。我们提供了新生代放射虫壳重量变化的两个组成部分——尺寸和硅化的数据。在低纬度地区，新生代硅藻向深水区输出二氧化硅的增加，以及水柱分层增加导致营养物上涌的减少，造成了现代贫硅地表水。在此，放射虫硅化显着降低（r = 0.91，P < 0.001），从基底新生代的约 0.18（壳体积分数）降至现代值约 0.06。总变化的三分之一在 35 Ma 时迅速发生，与水体分层和硅藻丰度的大幅增加相关。在南部高纬度地区，自始新世晚期以来就存在的南大洋环流维持着大量的地表水二氧化硅可用性。在此，放射虫硅化程度微弱下降（r = 0.58，P = 0.1），从 35 Ma 时的 ≈0.13 下降到今天的 0.11。两个时间序列中壳尺寸的趋势在统计上并不显着，并且彼此不相关。我们的结论是，不存在改变新生代海洋浮游生物细胞大小的通用驱动因素。此外，生物和物理因素共同减少了地表水中的二氧化硅含量，迫使新生代低纬度放射虫发生宏观进化变化。
It has been hypothesized that increased water column stratification has been an abiotic “universal driver” affecting average cell size in Cenozoic marine plankton. Gradually decreasing Cenozoic radiolarian shell weight, by contrast, suggests that competition for dissolved silica, a shared nutrient, resulted in biologic coevolution between radiolaria and marine diatoms, which expanded dramatically in the Cenozoic. We present data on the 2 components of shell weight change—size and silicification—of Cenozoic radiolarians. In low latitudes, increasing Cenozoic export of silica to deep waters by diatoms and decreasing nutrient upwelling from increased water column stratification have created modern silica-poor surface waters. Here, radiolarian silicification decreases significantly (r = 0.91, P < 0.001), from ≈0.18 (shell volume fraction) in the basal Cenozoic to modern values of ≈0.06. A third of the total change occurred rapidly at 35 Ma, in correlation to major increases in water column stratification and abundance of diatoms. In high southern latitudes, Southern Ocean circulation, present since the late Eocene, maintains significant surface water silica availability. Here, radiolarian silicification decreased insignificantly (r = 0.58, P = 0.1), from ≈0.13 at 35 Ma to 0.11 today. Trends in shell size in both time series are statistically insignificant and are not correlated with each other. We conclude that there is no universal driver changing cell size in Cenozoic marine plankton. Furthermore, biologic and physical factors have, in concert, by reducing silica availability in surface waters, forced macroevolutionary changes in Cenozoic low-latitude radiolarians.