Environmental stability affects phenotypic evolution in a globally distributed marine picoplankton

Abstract

Marine phytoplankton can evolve rapidly when confronted with aspects of climate change because of their large population sizes and fast generation times. Despite this, the importance of environment fluctuations, a key feature of climate change, has received little attention-selection experiments with marine phytoplankton are usually carried out in stable environments and use single or few representatives of a species, genus or functional group. Here we investigate whether and by how much environmental fluctuations contribute to changes in ecologically important phytoplankton traits such as C:N ratios and cell size, and test the variability of changes in these traits within the globally distributed species Ostreococcus. We have evolved 16 physiologically distinct lineages of Ostreococcus at stable high CO 2 (1031 ± 87 μatm CO 2 , SH) and fluctuating high CO 2 (1012 ± 244 μatm CO 2 , FH) for 400 generations. We find that although both fluctuation and high CO 2 drive evolution, FHevolved lineages are smaller, have reduced C:N ratios and respond more strongly to further increases in CO 2 than do SH-evolved lineages. This indicates that environmental fluctuations are an important factor to consider when predicting how the characteristics of future phytoplankton populations will have an impact on biogeochemical cycles and higher trophic levels in marine food webs.

Highest plasticity of carbon‐concentrating mechanisms in earliest evolved phytoplankton

“…Plasticity of traits can evolve through fluctuations in the environment (Agrawal ; Schaum et al ). Consequently, the ability to regulate CCMs may possibly also have been maintained under dynamic CO 2 concentrations.…”

Experimental strategies to assess the biological ramifications of multiple drivers of global ocean change—A review

“…In contrast, other studies show loss of function, or even trait reversion. In the marine alga Ostreococcus , an initial response to high CO 2 eventually reverses to some degree under constant high CO 2 conditions, and more or less completely under fluctuating CO 2 conditions (Schaum & Collins, ; Schaum, Rost, & Collins, ). Finally, traits may evolve to surpass the plastic response, which is the expected outcome under directional selection in an environment where fitness is initially low (Elena & Lenski, ).…”

Geographical CO2 sensitivity of phytoplankton correlates with ocean buffer capacity

“…Within experimental studies, significant physiological responses to altered carbonate chemistry for any given organism might be expected under those conditions where the magnitude and/or frequency of any imposed change exceeds that of current acclimative tolerance (Boyd et al., ; Denman, Christian, Steiner, Pörtner & Nojiri, ; Joint, Doney & Karl, ; Lewis, Brown, Edwards, Cooper & Findlay, ; Richier et al., ). In addition to dictating the response to experimental manipulation (Richier et al., ), differential acclimative potential across organisms may also influence the emergent outcome of community responses to the longer term environmental perturbation represented by OA (Hendricks et al., ; Lohbeck, Riebesell & Reusch, ; Reusch & Boyd, ; Schaum, Rost & Collins, ; Schaum, Rost, Millar & Collins, ). Indeed, differential sensitivity to dynamic changes in carbonate chemistry might be expected on the basis of theoretical considerations (Flynn et al., ) and has recently been demonstrated for phytoplankton, specifically between coastal and open ocean diatom taxa (Li, Wu, Hutchins, Fu & Gao, ).…”

“…Understanding the fundamental controls on acclimative tolerance to carbonate chemistry variability and adaptive differences in such tolerances between groups and across environmental gradients is essential for predicting natural phytoplankton community responses to OA‐type perturbations over space and time (Flynn et al., , ; Lewis et al., ; Li et al., ; Schaum et al., ). We, therefore, investigated whether differential responses in the sensitivity of phytoplankton to short‐term changes in the CCS were observable within natural communities, and whether such variability related to ocean‐scale gradients in environmental conditions.…”