Super-Species in the calcareous plankton

Abstract

SummaryThe most successful groups of pelagic protists in the modern Ocean have evolved convergent phenotypic traits, including the presence of hard skeletons enclosing the cell. These micro-skeletons -tests, coccoliths, frustules, theca -have accumulated kilometers of deep-sea sediments since the Jurassic, the most complete and continuous fossil record widely used for reconstructing Earth systems dynamics and microbial evolution. The use of the traditional morphological species concepts in those groups indicates that the relatively few species living at a given time have huge, often circum-global biogeographic distributions, and commonly last for many million years in the sediment record, which contrasts with the hectic biological pace of life occurring in the oceanic water masses, leading to one of the highest organismic turnover that any ecosystem sustains. Here we review all recent genetic data on coccolithophore and foraminifer biodiversity. In both groups, the sequencing of various genes shows that the morphological 'species' are in fact monophyletic assemblages of sibling species which diverged several million years ago according to molecular clock calculations. Furthermore the sibling species within a morphological entity may systematically occupy restricted geographic or temporal allopatric subdivisions of the total ecological range attributed to the traditional morphospecies. They display also stable and subtle -despite million years of genetic isolation -morphological differences that have been previously overlooked or interpreted as ecophenotypic variations. Obviously, various selective forces related to life in the marine planktic realm impose a strong stabilizing selection on pelagic organisms that maintains "optimal" phenotypes through the origination and possibly extinction of sibling species. We propose that this mode of evolution is characteristic of most marine planktic taxa, including metazoans, and we introduce a concept of 'planktic super-species' to describe these constrained morphological monophyletic entities that include several sibling species H. R. Thierstein et al. (eds.), Coccolithophores

Morphometric and stable isotopic differentiation of Orbulina universa morphotypes from the Cariaco Basin, Venezuela

“…Marine Micropaleontology 120 (2015) [46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] However, the significance of morphological variation was not apparent until the first genetic studies of foraminifera. These studies revealed that many morphologically defined species are complexes of cryptic genetic variants (Darling et al, 1996(Darling et al, , 1999de Vargas et al, 1997de Vargas et al, , 1999de Vargas et al, , 2003Huber et al, 1997;Kucera and Darling, 2002;Darling and Wade, 2008). For example, fifty-four cryptic species have been identified among nine modern planktonic foraminiferal morphospecies commonly used for paleoceanographic reconstructions (Kucera and Darling, 2002;Darling and Wade, 2008;Morard et al, 2013).…”

“…For example, fifty-four cryptic species have been identified among nine modern planktonic foraminiferal morphospecies commonly used for paleoceanographic reconstructions (Kucera and Darling, 2002;Darling and Wade, 2008;Morard et al, 2013). Several studies suggest that cryptic species can differ in their ecological preferences (Huber et al, 1997;Darling et al, 1999;de Vargas et al, 1999de Vargas et al, , 2003Stewart et al, 2001;Kuroyanagi and Kawahata, 2004;Morard et al, 2009Morard et al, , 2013Aurahs et al, 2011) and emphasize the importance of distinguishing between genotypes for paleoceanographic reconstructions (Kucera and Darling, 2002). Based on these findings, it is likely that a morphotype/genotype "lumping" approach for geochemical, morphometric and distribution analyses introduces a significant amount of noise into paleoclimate records.…”

Methodology for Single-Cell Genetic Analysis of Planktonic Foraminifera for Studies of Protist Diversity and Evolution

“…The term "single-cell approach" refers to a method, which involves the extraction, amplification and sequencing of DNA from an individual living unicellular organism. Using this approach in marine protists with skeletal frameworks, DNA sequences can be directly associated with morphology, allowing the revision of species limits (e.g., Harper et al, 2009) and discovering the extent of cryptic diversity within morphologically defined species (e.g., de Vargas et al, 1999Vargas et al, , 2004. The application of a single-cell approach is a necessity in all groups of protists that cannot be cultured to the stage of reproduction in the laboratory.…”

Morphological variation in the deep ocean-dwelling coccolithophoreFlorisphaera profunda(Haptophyta)

“…Such morphological groups may in fact represent different species which diverged several million years ago, as already demonstrated for other microscopic planktonic organisms e.g., planktonic foraminifera (Darling et al, 1996;Norris & de Vargas, 2000;de Vargas et al, 2004). These findings are crucial to understanding the biodiversity, ecology and evolution of coccolithophores as well as for their application as proxies in palaeoenvironmental reconstructions (Bollmann et al, 2002).…”

“…20%) of all living coccolithophore species have so far been cultured (Probert & Houdan, 2004) and the taxonomy of this phytoplankton group therefore remains mainly based on the morphology of their calcareous skeletons. Nevertheless, the application of new techniques for the combined morphometric and molecular genetic analysis of microscopic plankton (de Vargas et al, 2004) is likely to improve this situation.…”