Abstract
The overall mean levels of different environmental variables are changing rapidly in the present Anthropocene, in some cases creating lethal conditions for organisms. Under this new scenario, it is crucial to know whether the adaptive potential of organisms allows their survival under different rates of environmental change. Here, we used an eco‐evolutionary approach, based on a ratchet protocol, to investigate the effect of environmental change rate on the limit of resistance to salinity of three strains of the toxic cyanobacterium Microcystis aeruginosa. Specifically, we performed two ratchet experiments in order to simulate two scenarios of environmental change. In the first scenario, the salinity increase rate was slow (1.5‐fold increase), while in the second scenario, the rate was faster (threefold increase). Salinity concentrations ranging 7–10 gL‐1 NaCl (depending on the strain) inhibited growth completely. However, when performing the ratchet experiment, an increase in salinity resistance (9.1–13.6 gL‐1 NaCl) was observed in certain populations. The results showed that the limit of resistance to salinity that M. aeruginosa strains were able to reach depended on the strain and on the rate of environmental change. In particular, a higher number of populations were able to grow under their initial lethal salinity levels when the rate of salinity increment was slow. In future scenarios of increased salinity in natural freshwater bodies, this could have toxicological implications due to the production of microcystin by this species.
Highlights
The response of organisms to increasing selection pressure initially occurs through the modification of gene expression during a period extending from hours to few days
Does the rate of environmental change modulate the limit of resistance to salinity? We found that the cultures of M. aeruginosa exposed to a slow rate of salinity increase were the least likely to become extinct and showed a higher limit of resistance to salinity than the cultures exposed to a fast rate of salinity increase
This is in agreement with other experimental studies, which demonstrated that slow rates of environmental change lead to less extinction, or better adapted populations (Collins & de Meaux, 2009; Perron et al, 2008,2006; Bell & Gonzalez, 2011; Killeen et al, 2017)
Summary
Recombination between and de novo mutation within individually selected genotypes becomes necessary for population survival (i.e., adaptation, Belfiore & Anderson, 2001; Borowitzka, 2018). It must be highlighted that most of the studies focused on the effect of increased salinity on M. aeruginosa assessed the performance of cells after only a few generations (less than ten) submitted to high salinity (Martínez de la Escalera et al, 2017; Miller et al, 2010; Rosen et al, 2018; Orr, Jones, & Douglas, 2004; Otsuka et al, 1999; Prinsloo & Pieterse, 1994; Tonk, Bosch, Visser, & Huisman, 2007; Verspagen et al, 2006; Zhang, Xu, & Xi, 2013) These results could be interpreted as evidence of cell regulation and acclimation (Borowitzka, 2018). A complementary experiment was performed to disentangle whether the observed limit of resistance to salinity was due to acclimation or to the selection of new genetic variants
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