Origin and Evolution of Coccolithophores. From Coastal Hunters to Oceanic Farmers.

Abstract

This chapter discusses the origin and evolution of coccolithophores and presents an up-to-date summary of coccolithophore evolution, integrating recent stratophenetic, molecular phylogenetic, biogeochemical, and biological data. A discussion is presented on the origin and nature of the haptophyte ancestors of coccolithophores, the origin of coccolithophores, and the onset of calcification. The chapter also illustrates different evolutionary trajectories that succeeding lineages have followed. This evolutionary scheme is then correlated to abiotic and biotic records of historical change in the Earth system, allowing us to evaluate the various extrinsic and possibly intrinsic genomic forces that have driven coccolithophore evolution and the resulting feedbacks of their evolution on the ecosystem. Finally, based on the interpretations of coccolithophore evolutionary history, an uncertain future for this clade in the high CO2 and high Mg/low Ca world of the Anthropocene is envisioned. This emerging monophyletic entity of potentially calcifying haptophytes has no formal scientific name, and here the erection of a new subclass, the Calcihaptophycidae is proposed. Further justification of this new taxonomic designation is provided in the chapter. An increasing number of species from across the phylogeny of the Prymnesiophyceae have been shown to exhibit haplodiploid life cycles. Furthermore, the seawater Mg: Ca ratio has shown a significant increase since the K/T, with the onset of a new, Neogene, Aragonite ocean. The modern Mg: Ca ratio of ∼5 is higher than ever before in the Phanerozoic and may significantly increase the metabolic cost to the Calcihaptophycidae of producing calcite coccoliths. © 2007 Elsevier Inc. All rights reserved.