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.

摘要

当适应防止致命选择下的灭绝时，就会发生进化拯救（ER）。然而，缺乏实证研究来解决促成 ER 的可能因素限制了我们在全球变化背景下对当前生物多样性危机的理解。在这里，我们讨论了环境恶化率和聚集种群的分散对暴露于致命盐度水平的淡水蓝藻铜绿微囊藻中 ER 动力学的作用。我们将M. aeruginosa暴露于两种环境恶化率的六种组合（控制 = 无恶化和渐进恶化）。逐渐恶化的人群开始使用五种不同的 NaCl 浓度（从 0 到 4 gl ^–1 NaCl），其中 2 gl ^–1每隔 4 周添加两次 NaCl，最后增加 4 g ^–1 NaCl。实验中的最终浓度范围为 8 至 12 g ^–1氯化钠。没有恶化治疗的人群在初始浓度下花费了 12 周，然后突然转移到最终浓度范围内。为了确定分散对 ER 事件数量的影响，实施了三种分散模式：（i）种群不混合（不分散）；(ii) 将 6 个具有相同 NaCl 浓度的重复种群混合在一起（局部分散）；(iii) 同一集合种群的所有种群混合在一起（全球扩散）。扩散模式和恶化率都是每个元种群中 ER 结果的非常强的预测因子。具体来说，人群之间的分散和先前的压力暴露有利于 ER 事件的发生。