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

Abstract

Phytoplankton may evolve complex plasticity that can affect biogeochemically important traits such as calcification.

Adaptive evolution in the coccolithophore Gephyrocapsa oceanica following 1,000 generations of selection under elevated CO2

“…This might impose a potential competitive disadvantage on G. oceanica and could have major ecological implications for this biogeochemically critical coccolithophore in the future high CO 2 ocean. In contrast, in the extensively studied E. huxleyi , the populations selected at increased CO 2 level exhibited higher growth rates after 500 asexual generations, and in the subsequent 4 years of selection, the growth rate adaptation continually increased (Schlüter et al., ). In these two closely related coccolithophore species, both of their growth rates decreased when exposed to elevated CO 2 for several generations, while long‐term exposure brought about completely opposite responses between them.…”

“…However, the response pattern was later reversed. By the end of the 4 years of selection, high CO 2 ‐adapted populations displayed more than 20% lower PIC compared to the immediate physiological decline of PIC in ambient CO 2 ‐selected populations (Schlüter et al., ). In G. oceanica , the long‐term exposure to high CO 2 resulted in a further 55% decrease in cellular PIC compared to the physiological decline, and outside the range of responses reported for both G. oceanica and E. huxleyi in previous short‐term studies (Beardall & Raven, ; Bodt, Oostende, Harlay, Sabbe, & Chou, ; Borchard, Borges, Händel, & Engel, ).…”

“…Their results demonstrated the possibility for adaptation to ocean acidification in this key phytoplankton species both through de novo mutations in single clone assays, and genotypic selection in multiclone assays (Lohbeck et al., ; Schlüter et al., ). In the subsequent years, however, no further fitness increases were observed in high CO 2 ‐selected populations, and calcification in particular reverted to a level lower than that of the ambient CO 2 ‐selected populations (Schlüter, Lohbeck, Gröger, Riebesell, & Reusch, ).…”

Over-calcified forms of the coccolithophore <i>Emiliania huxleyi</i> in high-CO<sub>2</sub> waters are not preadapted to ocean acidification

“…Such adaptive capacity to high-CO 2 -low-pH conditions has been suggested for E. huxleyi in long-term lab-based experimental evolution studies (up to 2000 generations) on clonal strains (Lohbeck et al, 2012;Schlüter et al, 2016). It is still difficult to know to which extent such experiments reflect real-world adaptation processes.…”

“…For example, in paleo-oceans, it might have helped alleviate toxicity from Ca 2+ when levels reached up to 4-fold higher than in the modern ocean during the Cretaceous (Müller et al, 2015b). The long-term and nonlinear declines in calcification observed in experimental adaptation to high CO 2 and low pH (Schlüter et al, 2016) thus might have a high potential cost if such changes occurred in nature.…”