Lazarus David B, Kotrc Benjamin, Wulf Gerwin, Schmidt Daniela N
Museum für Naturkunde, Berlin, Germany.
Proc Natl Acad Sci U S A. 2009 Jun 9;106(23):9333-8. doi: 10.1073/pnas.0812979106. Epub 2009 May 20.
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 approximately 0.18 (shell volume fraction) in the basal Cenozoic to modern values of approximately 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 approximately 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.
据推测，水柱分层加剧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，新生代放射虫壳重逐渐降低，这表明对溶解硅（一种共享营养物质）的竞争导致了放射虫与海洋硅藻之间的生物共同进化，而海洋硅藻在新生代急剧扩张。我们展示了关于新生代放射虫壳重变化的两个组成部分——大小和硅化作用——的数据。在低纬度地区，新生代硅藻向深水输出的硅增加，以及水柱分层加剧导致营养物质上升流减少，造成了现代贫硅的表层水。在这里，放射虫的硅化作用显著降低（r = 0.91，P < 0.001），从新生代早期的约0.18（壳体积分数）降至现代的约0.06。总变化的三分之一在3500万年前迅速发生，与水柱分层和硅藻丰度的大幅增加相关。在高南纬地区，自始新世晚期以来存在的南大洋环流维持了表层水显著的硅可用性。在这里，放射虫的硅化作用下降不显著（r = 0.58，P = 0.1），从3500万年前的约0.13降至如今的0.11。两个时间序列中壳大小的趋势在统计上不显著，且彼此不相关。我们得出结论，在新生代海洋浮游生物中不存在改变细胞大小的普遍驱动因素。此外，生物和物理因素共同作用，通过降低表层水中硅的可用性，迫使新生代低纬度放射虫发生宏观进化变化。
