Dispersal of populations and environmental deterioration rate influence evolutionary rescue under selection by salinity in the freshwater cyanobacterium Microcystis aeruginosa

ABSTRACT

Evolutionary rescue (ER) occurs when adaptation prevents extinction under lethal selection. However, the lack of empirical studies addressing the possible factors enabling ER limits our understanding of the current biodiversity crisis in the context of global change. Here we addressed the roles of environmental deterioration rate and dispersal of metapopulations on the dynamics of ER in the freshwater cyanobacterium Microcystis aeruginosa exposed to lethal salinity levels. We exposed M. aeruginosa to six combinations of two environmental deterioration rates (control = no deterioration, and progressive deterioration). Populations under progressive deterioration started with five different NaCl concentrations (from 0 to 4 g l^–1 NaCl), with 2 g l^–1 NaCl added twice at 4-week intervals, followed by a final increase of 4 g l^–1 NaCl. Final concentrations in the experiment ranged from 8 to 12 g l^–1 NaCl. Populations with no deterioration treatment spent 12 weeks in the initial concentration and were suddenly shifted to the final range concentration. To determine the effects of dispersal on the number of ER events, three dispersal modes were implemented: (i) populations were not mixed (no dispersal); (ii) six replicate populations of the same NaCl concentration were mixed together (local dispersal); and (iii) all populations of the same metapopulation were mixed together (global dispersal). Both dispersal mode and deterioration rate were very strong predictors of the ER outcome in each metapopulation. Specifically, dispersal among populations and prior stress exposure favoured the occurrence of ER events.

KEYWORDS:

• Evolutionary rescue
• experimental evolution
• metapopulation
• Microcystis aeruginosa
• salinity

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary information

The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at https://doi.org/10.1080/09670262.2021.1896787

Supplementary table S1. Gross data for the first experiment of evolutionary rescue. Data are the weekly growth rate of the six experimental populations (m1–m6; units on day^–1) at different initial salinities (S; from 0 to 4 g l^–1 NaCl), under the six combinations of dispersal and deterioration rates (A–E). Grey background (weeks 13–16) corresponds to the evolutionary rescue phase. (A) Without dispersal and without deterioration. (B) Local dispersal and without deterioration. (C) Global dispersal and without deterioration. (D) Without dispersal and progressive deterioration. (E) Local dispersal and progressive deterioration. (F) Global dispersal and progressive deterioration.

Supplementary table S2. Gross data for the second experiment of evolutionary rescue. Data are the weekly growth rate of the six experimental populations (m1–m6; units in day^–1) at different initial salinities (S; from 0 to 4 g l^–1 NaCl), under the six combinations of dispersal and deterioration rates (A–F). Grey background (weeks 13–16) corresponds to the evolutionary rescue phase. (A) Without dispersal and without deterioration. (B) Local dispersal and without deterioration. (C) Global dispersal and without deterioration. (D) Without dispersal and progressive deterioration. (E) Local dispersal and progressive deterioration. (F) Global dispersal and progressive deterioration.

Supplementary table S3. Gross data for the third experiment of evolutionary rescue. Data are the weekly growth rate of the six experimental populations (m1–m6; units in day⁻¹) at different initial salinities (S; from 0 to 4 g l^–1 NaCl), under the six combinations of dispersal and deterioration rates (A–F). Grey background (weeks 13–16) corresponds to the evolutionary rescue phase. (A) Without dispersal and without deterioration. (B) Local dispersal and without deterioration. (C) Global dispersal and without deterioration. (D) Without dispersal and progressive deterioration. (E) Local dispersal and progressive deterioration. (F) Global dispersal and progressive deterioration.

Supplementary table S4. Gross data for the fourth experiment of evolutionary rescue. Data are the weekly growth rate of the six experimental populations (m1–m6; units in day⁻¹) at different initial salinities (S; from 0 to 4 g l^–1 NaCl), under the six combinations of dispersal and deterioration rates (A–F). Grey background (weeks 13–16) corresponds to the evolutionary rescue phase. (A) Without dispersal and without deterioration. (B) Local dispersal and without deterioration. (C) Global dispersal and without deterioration. (D) Without dispersal and progressive deterioration. (E) Local dispersal and progressive deterioration. (F) Global dispersal and progressive deterioration.

Author contributions

IJM-J performed the experiments, analysed the data, wrote the paper, prepared figures and tables, and reviewed drafts of the paper; EM-C performed the experiments; AR wrote the paper and reviewed drafts of the paper; MJG-S and AF-M conceived and designed the experiments, analysed the data, contributed reagents/materials/analysis tools, wrote the paper and reviewed drafts of the paper; EBE conceived and designed the experiments, analysed the data and reviewed drafts of the paper.

Additional information

Funding

This work was financially supported by the project CGL2014-53862-P (Ministerio de Economía y Competitividad) and the project CGL2017-87314-P (Ministerio de Economía, Industria y Competitividad). EM-C was funded by BES-2015-072984 grant. Dr Eric C. Henry kindly revised the English style and usage.