Life-cycle modification in open oceans accounts for genome variability in a cosmopolitan phytoplankton

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von Dassow, Peter
John, Uwe
Ogata, Hiroyuki
Probert, Ian
Bendif, El Mahdi
Kege, Jessica U.
Audic, Stephane
Wincker, Patrick
Da Silva, Corinne
Claverie, Jean-Michel
Doney, Scott C.
Glover, David M.
Flores, Daniella Mella
Herrera, Yeritza
Lescot, Magali
Garet-Delmas, Marie-Jose
de Vargas, Colomban
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Emiliania huxleyi is the most abundant calcifying plankton in modern oceans with substantial intraspecific genome variability and a biphasic life cycle involving sexual alternation between calcified 2N and flagellated 1N cells. We show that high genome content variability in Emiliania relates to erosion of 1N-specific genes and loss of the ability to form flagellated cells. Analysis of 185 E. huxleyi strains isolated from world oceans suggests that loss of flagella occurred independently in lineages inhabiting oligotrophic open oceans over short evolutionary timescales. This environmentally linked physiogenomic change suggests life cycling is not advantageous in very large/diluted populations experiencing low biotic pressure and low ecological variability. Gene loss did not appear to reflect pressure for genome streamlining in oligotrophic oceans as previously observed in picoplankton. Life-cycle modifications might be common in plankton and cause major functional variability to be hidden from traditional taxonomic or molecular markers.
© International Society for Microbial Ecology, 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in ISME Journal 9 (2015): 1365–1377, doi:10.1038/ismej.2014.221.
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ISME Journal 9 (2015): 1365–1377
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