Kucera Michal, Darling Kate F
Department of Geology, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK.
Philos Trans A Math Phys Eng Sci. 2002 Apr 15;360(1793):695-718. doi: 10.1098/rsta.2001.0962.
Shells of planktonic foraminifera recovered from marine sediments provide a multitude of important palaeoproxies. Most of these proxies are based on the assumption that each morphospecies of planktonic foraminifera represents a genetically continuous species with a unique habitat. Recent discovery of hitherto hidden genetic diversity among modern planktonic foraminifera has significant repercussions on palaeoproxies derived from their fossil shells. We have compiled all available data on this genetic diversity. To date, 33 cryptic genetic types were found in 9 out of the 22 sequenced morphospecies of modern planktonic foraminifera. An examination of this database suggests that cryptic genetic diversity may be a prevalent pattern among modern planktonic foraminifera, but that the total number of cryptic genetic types per morphospecies is not large and that most genetic types show a non-random pattern of distribution in the oceans. Using modern distribution data from the Atlantic Ocean as constraints, the relationship between abundances of three genetic types of Globigerina bulloides and sea-surface temperature has been modelled and this model has been applied to a database of species counts in Atlantic coretops (761 samples). Trials with artificial neural networks (ANNs), the modern analogue technique and Imbrie-Kipp transfer functions showed that the splitting of G. bulloides into three genetic types resulted in substantial reduction in the prediction error rate (by 5 to 34%) and that this improvement was by far greatest in ANN trials (on average more than 20%). We conclude that such a large reduction in error rate occurred because the models resonated with a real pattern in the original data. This study indicates that genetic diversity among planktonic foraminifera may become more of a gift than malaise to palaeoproxies. If it becomes possible to distinguish these genetic types in the fossil record, the accuracy of proxies based on planktonic foraminifera will indeed substantially increase.
从海洋沉积物中回收的浮游有孔虫壳提供了许多重要的古环境指标。这些指标大多基于这样一种假设，即浮游有孔虫的每个形态物种都代表一个具有独特栖息地的基因连续的物种。最近在现代浮游有孔虫中发现的迄今隐藏的遗传多样性，对源自其化石壳的古环境指标产生了重大影响。我们汇编了关于这种遗传多样性的所有可用数据。迄今为止，在现代浮游有孔虫的22个已测序形态物种中的9个中发现了33种隐性遗传类型。对该数据库的检查表明，隐性遗传多样性可能是现代浮游有孔虫中的普遍模式，但每个形态物种的隐性遗传类型总数并不多，而且大多数遗传类型在海洋中呈现非随机分布模式。利用来自大西洋的现代分布数据作为约束条件，对布氏球石藻三种遗传类型的丰度与海面温度之间的关系进行了建模，并将该模型应用于大西洋岩芯顶部物种计数数据库（761个样本）。使用人工神经网络（ANN）、现代类比技术和英布里 - 基普传递函数进行的试验表明，将布氏球石藻分为三种遗传类型导致预测误差率大幅降低（降低了5%至34%），并且这种改进在ANN试验中最为显著（平均超过20%）。我们得出结论，误差率如此大幅降低是因为模型与原始数据中的真实模式相契合。这项研究表明，浮游有孔虫中的遗传多样性对古环境指标而言可能更多是一种恩赐而非麻烦。如果能够在化石记录中区分这些遗传类型，基于浮游有孔虫的指标的准确性确实将大幅提高。
