Probert Ian

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Probert
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Ian
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  • Article
    Decrease in coccolithophore calcification and CO2 since the middle Miocene
    (Nature Publishing Group, 2016-01-14) Bolton, Clara T. ; Hernandez-Sanchez, Maria T. ; Fuertes, Miguel-Ángel ; Gonzalez-Lemos, Saul ; Abrevaya, Lorena ; Mendez-Vicente, Ana ; Flores, Jose-Abel ; Probert, Ian ; Giosan, Liviu ; Johnson, Joel E. ; Stoll, Heather M.
    Marine algae are instrumental in carbon cycling and atmospheric carbon dioxide (CO2) regulation. One group, coccolithophores, uses carbon to photosynthesize and to calcify, covering their cells with chalk platelets (coccoliths). How ocean acidification influences coccolithophore calcification is strongly debated, and the effects of carbonate chemistry changes in the geological past are poorly understood. This paper relates degree of coccolith calcification to cellular calcification, and presents the first records of size-normalized coccolith thickness spanning the last 14 Myr from tropical oceans. Degree of calcification was highest in the low-pH, high-CO2 Miocene ocean, but decreased significantly between 6 and 4 Myr ago. Based on this and concurrent trends in a new alkenone εp record, we propose that decreasing CO2 partly drove the observed trend via reduced cellular bicarbonate allocation to calcification. This trend reversed in the late Pleistocene despite low CO2, suggesting an additional regulator of calcification such as alkalinity.
  • Article
    Life-cycle modification in open oceans accounts for genome variability in a cosmopolitan phytoplankton
    (Nature Publishing Group, 2014-12-02) 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
    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.