Am Nat. 2023 Jun;201(6):825-840. doi: 10.1086/724417. Epub 2023 Apr 14.
AbstractEnvironmentally induced reductions in fitness components (survival, fecundity) are generally considered as passive, maladaptive responses to stress. However, there is also mounting evidence for active, programmed forms of environmentally induced cell death in unicellular organisms. While conceptual work has questioned how such programmed cell death (PCD) might be maintained by natural selection, few experimental studies have investigated how PCD influences genetic differences in longer-term fitness across environments. Here, we tracked the population dynamics of two closely related strains of the halotolerant microalga following transfers across salinities. We showed that after a salinity increase, only one of these strains displayed a massive population decline (-69% in 1 h), largely attenuated by exposure to a PCD inhibitor. However, this decline was followed by a rapid demographic rebound, characterized by faster growth than the nondeclining strain, such that sharper decline was correlated with faster subsequent growth across experiments and conditions. Strikingly, the decline was more pronounced in conditions more favorable to growth (more light, more nutrients, less competition), further suggesting that it was not simply passive. We explored several hypotheses that could explain this decline-rebound pattern, which suggests that successive stresses could select for higher environmentally induced death in this system.
摘要 环境引起的适应力成分（生存、繁殖力）下降通常被认为是生物体对压力的被动、适应不良的反应。然而，越来越多的证据表明，单细胞生物中存在着主动的、程序化的环境诱导细胞死亡形式。虽然概念性工作对这种程序化细胞死亡（PCD）如何通过自然选择得到维持提出了质疑，但很少有实验研究调查 PCD 如何影响在不同环境中长期适应力的遗传差异。在这里，我们跟踪了两种耐盐微藻密切相关的品系在盐度变化后的种群动态。我们发现，在盐度增加后，只有其中一种品系的种群大量减少（在 1 小时内减少了 69%），而 PCD 抑制剂的暴露大大减轻了这种减少。然而，这种下降之后是一个快速的人口反弹，其特征是比不下降的品系增长更快，因此在实验和条件下，更明显的下降与随后更快的增长相关。引人注目的是，在更有利于生长的条件下（更多的光、更多的营养物质、更少的竞争），下降更为明显，这进一步表明这并不是简单的被动反应。我们探讨了几种假说，这些假说可以解释这种下降-反弹模式，这表明在这个系统中，连续的压力可能会选择更高的环境诱导死亡。
