Data from: The ontogeny of tolerance curves: habitat quality vs. acclimation in a stressful environment

Stressful environments affect life-history components of fitness through (i) instantaneous detrimental effects, (ii) historical (carry-over) effects and (iii) history-by-environment interactions, including acclimation effects. The relative contributions of these different responses to environmental stress are likely to change along life, but such ontogenic perspective is often overlooked in studies of tolerance curves, precluding a better understanding of the causes of costs of acclimation, and more generally of fitness in temporally fine-grained environments.
We performed an experiment in the brine shrimp Artemia to disentangle these different contributions to environmental tolerance, and investigate how they unfold along life. We placed individuals from three clones of A. parthenogenetica over a range of salinities during a week, before transferring them to a (possibly) different salinity for the rest of their lives. We monitored individual survival at repeated intervals throughout life, instead of measuring survival or performance at a given point in time, as commonly done in acclimation experiments. We then designed a modified survival analysis model to estimate phase-specific hazard rates, accounting for the fact that individuals may share the same treatment for only part of their lives.
Our approach allowed us to distinguish effects of salinity on (i) instantaneous mortality in each phase (habitat quality effects), (ii) mortality later in life (history effects) and (iii) their interaction. We showed clear effects of early salinity on late survival and interactions between effects of past and current environments on survival. Importantly, analysis of the ontogenetic dynamics of the tolerance curve reveals that acclimation affects different parts of the curve at different ages.
Adopting a dynamical view of the ontogeny of tolerance curve should prove useful for understanding niche limits in temporally changing environments, where the full sequence of environments experienced by an individual determines its overall environmental tolerance, and how it changes throughout life.

胁迫环境可通过三种途径影响物种适合度的生活史组分：(i) 瞬时有害效应、(ii) 历史（遗留）效应，以及(iii) 历史-环境交互效应（含驯化效应（acclimation））。上述不同响应对环境胁迫的相对贡献度很可能随个体发育进程发生改变，但这类个体发育视角在耐受曲线研究中常被忽视，这不仅阻碍了我们对驯化代价成因的深入理解，更难以解析这类随时间精细变化环境中物种适合度的维持机制。
本研究以卤虫（Artemia）为实验对象，旨在解析环境耐受能力的上述不同贡献来源，并探究其随个体发育的动态变化过程。我们将3株孤雌生殖卤虫（A. parthenogenetica）的个体置于一系列盐度梯度下培养一周，随后将其转移至（可能不同的）盐度环境中直至生命结束。不同于现有驯化实验中常见的单时间点存活或表现测定方式，我们在个体整个生命周期内以固定间隔多次监测其存活情况。此外，我们构建了改良的存活分析模型以估算阶段特异性死亡风险率，该模型考虑了个体仅在生命部分阶段接受相同处理的实际情况。
本研究方法得以区分盐度对以下三方面的影响：(i) 各阶段的瞬时死亡率（生境质量效应）、(ii) 生命后期的死亡率（历史效应），以及(iii) 二者的交互效应。我们发现早期盐度暴露对后期存活具有显著影响，且过往与当前环境的效应之间存在交互作用。值得注意的是，对耐受曲线的个体发育动态分析显示，驯化效应在不同年龄阶段会作用于耐受曲线的不同区段。
采用耐受曲线个体发育的动态视角，将有助于理解随时间变化环境中的物种生态位边界：个体所经历的完整环境序列决定了其整体环境耐受能力，以及该能力随生命进程的动态变化。