Interactive effects of immediate and ancestral salt stress on fitness in duckweed

AbstractPremise of Research Organisms that reproduce asexually must respond to abiotic stresses in their environment while contending with the potential disadvantage of the reduced ability for genetic variation through recombination. Common duckweed (Lemna minor) is an aquatic plant that reproduces predominantly asexually through the budding of ramets. As a freshwater plant, duckweed experiences stress from salt (e.g., NaCl), which detrimentally affects growth, photosynthesis, and cellular processes. We took a demographic approach to examine whether ancestral exposure to salt stress affects the ability of duckweed offspring to tolerate immediate exposure to the same stress. Methodology We placed three consecutive clonal generations of duckweed in an environment with 2 g L-1 NaCl (non-lethal salt stress) or 0 g L-1 NaCl (control), followed by an additional 0-3 generations in the control environment to vary the presence and schedule of ancestral stress. After these treatments, we used the offspring produced as focal plants for the experiment. Half were placed into the salt-stress environment, and half were placed in control conditions, and focal plants were tracked longitudinally. Pivotal Results Immediate stress decreased fitness, due to a slowing of reproduction, suggesting a cost of stress tolerance. The effects of ancestral stress, and the interaction of immediate and ancestral stress, were more complex. Specifically, recent ancestral stress induced plants to produce offspring more quickly, but with the potential cost of lowered offspring quality. Conclusions Our results amplify findings that responses to, and fitness consequences of, current stressors can be contingent on past exposure.
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摘要：研究背景 进行无性繁殖的生物，在应对环境中非生物胁迫（abiotic stresses）的同时，还需面对因重组导致遗传变异能力降低所带来的潜在劣势。小浮萍（Lemna minor）是一种常见水生植物，主要通过分株（ramets）出芽进行无性繁殖。作为淡水植物，小浮萍会遭受盐胁迫（例如氯化钠NaCl），该胁迫会对其生长、光合作用及细胞过程产生不利影响。本研究采用种群统计学方法，探究祖先暴露于盐胁迫是否会影响小浮萍后代对同一胁迫的即时耐受能力。
研究方法 我们将连续三代克隆世代（clonal generations）的小浮萍置于含有2 g·L⁻¹氯化钠（非致死盐胁迫）或0 g·L⁻¹氯化钠（对照组）的环境中培养，随后在对照环境中继续培养0至3代，以调整祖先胁迫的存在状态与施加时序。经上述处理后，将所得后代作为本实验的目标植株，其中一半被置于盐胁迫环境，另一半置于对照条件下，并对目标植株进行纵向追踪监测。
核心结果 即时盐胁迫会通过延缓繁殖速率降低植株适合度（fitness），这暗示了胁迫耐受存在一定的适应代价。祖先胁迫的影响，以及即时胁迫与祖先胁迫的交互作用则更为复杂。具体而言，近期经历过祖先胁迫的植株会更快产生后代，但这可能伴随后代品质降低的潜在代价。
研究结论 本研究结果进一步证实，生物对当前胁迫的响应及其对适合度的影响，会依赖于过往的胁迫暴露经历。
使用说明 运行本脚本需依赖R软件。