title: Variable but persistent coexistence of Prochlorococcus ecotypes along temperature gradients in the ocean's surface mixed layer.
abstract: The vast majority of the phytoplankton communities in surface mixed layer of the oligotrophic ocean are numerically dominated by one of two ecotypes of Prochlorococcus, eMIT9312 or eMED4. In this study, we surveyed large latitudinal transects in the Atlantic and Pacific Ocean to determine if these ecotypes discretely partition the surface mixed layer niche, or if populations exist as a continuum along key environmental gradients, particularly temperature. Transitions of dominance occurred at approximately 19-21°C, with the eMED4 ecotype dominating the colder, and eMIT9312 ecotype dominating the warmer regions. Within these zones of regional dominance, however, the minority ecotype was not competed to extinction. Rather, a robust log-linear relationship between ecotype ratio and temperature characterized this stabilized coexistence: for every 2.5°C increase in temperature, the eMIT9312:eMED4 ratio increased by an order of magnitude. This relationship was observed in both quantitative polymerase chain reaction and in pyrosequencing assays. Water column stratification also contributed to the ecotype ratio along the basin-scale transects, but to a lesser extent. Finally, instances where the ratio of the eMED4 and eMIT9312 abundances did not correlate well with temperature were identified. Such occurrences are likely due to changes in water temperatures outpacing changes in community structure.
authors.affiliation: Department of Microbiology, The University of Tennessee, M409 WLS, Knoxville, TN, 37966, USA.
authors.forename: Jeremy W
authors.initials: JW
authors.lastname: Chandler
authors.affiliation: Nicholas School of the Environment and Earth Sciences, Duke University, 135 Marine Lab Rd., Beaufort, NC, 28516, USA.
authors.forename: Yajuan
authors.initials: Y
authors.lastname: Lin
authors.affiliation: Department of Microbiology, The University of Tennessee, M409 WLS, Knoxville, TN, 37966, USA.
authors.forename: P Jackson
authors.initials: PJ
authors.lastname: Gainer
authors.affiliation: Graduate School of Oceanography, The University of Rhode Island, 220 South Ferry Road, Narragansett, RI, 02882, USA.
authors.forename: Anton F
authors.initials: AF
authors.lastname: Post
authors.affiliation: Nicholas School of the Environment and Earth Sciences, Duke University, 135 Marine Lab Rd., Beaufort, NC, 28516, USA.
authors.forename: Zackary I
authors.initials: ZI
authors.lastname: Johnson
authors.affiliation: Department of Microbiology, The University of Tennessee, M409 WLS, Knoxville, TN, 37966, USA.
authors.forename: Erik R
authors.initials: ER
authors.lastname: Zinser
mesh_terms: D001267:Atlantic Ocean; D058448:Biota; D060146:Ecotype; D010140:Pacific Ocean; D048929:Prochlorococcus / Q000145:classification* / Q000302:isolation & purification* / Q000528:radiation effects; D060888:Real-Time Polymerase Chain Reaction; D012623:Seawater / Q000382:microbiology*; D017422:Sequence Analysis, DNA; D013696:Temperature