Research ArticleAQUATIC ECOLOGY

Long-term dynamics of adaptive evolution in a globally important phytoplankton species to ocean acidification

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Science Advances  08 Jul 2016:
Vol. 2, no. 7, e1501660
DOI: 10.1126/sciadv.1501660
  • Fig. 1 Long-term phenotypic changes in replicated batch cultures of E. huxleyi under control and OA conditions.

    (A and B) Time course of specific daily growth rate (A) and cell diameter (B) over 4 years of selection to three different Pco2 levels, simulating OA. Growth rates and cell sizes were calculated every 5 days upon transfer of batch cultures. All lines reveal highly significant slopes that are not significantly different among CO2 treatments. Because we were not specifically interested in detecting a response level difference but differences in the time trends (that is, slopes), and as temporal variables are usually autocorrelated, the trend lines were not estimated on the basis of simple regression but using a series of ARMAX models (including transfer functions; for details, see Materials and Methods).

  • Fig. 2 Adaptive response of E. huxleyi to selection under three Pco2 levels simulating OA.

    Adaptive response over 4 years measured during assay experiments at five time points (x axis, average generations of all three CO2 treatments), always comparing medium CO2–adapted (left) and high CO2–adapted (right) versus nonadapted populations of E. huxleyi in three different CO2 environments, when assayed under elevated CO2 (mean ± SD, n = 5). (A and B) Exponential growth rate. (C and D) Cell diameter. (E and F) POC per cell. (G and H) PIC per cell. (I and J) Ratio of PIC/POC. Significant results of main and interaction effects are depicted with asterisks (*0.05 ≥ P > 0.01, **0.01 ≥ P > 0.001, ***P < 0.001). Complete rmANOVA results are given in table S1. The correlated response, that is, the performance of all high CO2 selection treatments under ambient CO2, is presented in fig. S1.

  • Fig. 3 End-point reaction norms of E. huxleyi populations selected under ambient and high CO2 conditions as a function of the assay condition.

    (A to H) Daily growth rate (A and B), POC (C and D), PIC (E and F), and PIC/POC ratio (G and H) after 2100 generations of evolution (~4 years). Given are means (±1 SD, n = 5). Significant results of planned contrasts are given only for the adaptation response (that is, under elevated CO2) and are indicated by asterisks (*0.05 ≥ P > 0.01, **0.01 ≥ P > 0.001, ***P < 0.001).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/7/e1501660/DC1

    fig. S1. Correlated response of E. huxleyi adapted to elevated CO2 levels.

    fig. S2. Adaptive response of E. huxleyi: PIC and POC cell quotas standardized to cell volume.

    table S1. Statistical analysis (rmANOVA) of the adaptive response of E. huxleyi (cf. Fig. 2 and fig. S2).

    table S2. Statistical analysis (two-way ANOVA) of the reciprocal assay in E. huxleyi at the end of the experiment (cf. Fig. 3).

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Correlated response of E. huxleyi adapted to elevated CO2 levels.
    • fig. S2. Adaptive response of E. huxleyi : PIC and POC cell quotas standardized to cell volume.
    • table S1. Statistical analysis (rmANOVA) of the adaptive response of E. huxleyi (cf. Fig. 2 and fig. S2).
    • table S2. Statistical analysis (two-way ANOVA) of the reciprocal assay in E. huxleyi at the end of the experiment (cf. Fig. 3).

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