Data from: Loss of heterosis and family-dependent inbreeding depression in plant performance and resistance against multiple herbivores under drought stress

1. Inbreeding depression (ID), outbreeding depression (OD) and heterosis can occur concurrently in plant populations. ID often increases under environmental stress, but the combined effects of inbreeding, outbreeding between populations and environmental stress, such as drought, on plant performance and herbivore resistance remain unclear. 2. In order to determine environment-dependent and family-dependent ID, OD and heterosis we conducted a common garden experiment with plants from five populations of Brassica nigra. Inbred, within-population outbred and between-population outbred plant families were exposed to drought or ambient water levels. We recorded the abundance and damage caused by specialist herbivores from contrasting feeding guilds, i.e. the phloem-feeding Brevicoryne brassicae, the leaf-chewing Psylliodes chrysocephalus and the stem-boring Ceutorhynchus quadridens larvae. 3. Drought stress had negative effects on growth, herbivore resistance and resistance against B. brassicae and positive effects on investments in reproductive output and plant secondary metabolites (sinigrin). We found drought stress-induced loss of heterosis for plant height and investment in reproductive output. Between-population outbred plants were more sensitive to drought stress in terms of above-ground biomass compared to within-population outbred plants. 4. Drought and inbreeding synergistically negatively influenced traits related to growth and reproductive output (environment-dependent inbreeding depression, EDID). There was high variation among families within populations in the degree of ID and EDID. Genetic variation in EDID could buffer the negative effects of genetic stress associated with habitat fragmentation and concurrent environmental stress. In order to capture fully the effects of both inbreeding and between-population outbreeding under stress the different spatial scales of the effects of inbreeding and between-population outbreeding should be taken into account. 5. Synthesis. Our results indicate that drought stress influences not only inbreeding depression (ID), but also heterosis. These findings shed new light on the combined effects of anthropogenic environmental change and the genetic consequences of habitat fragmentation on plants and their interactions with other organisms. Conservation programmes aiming to restore genetically degraded populations with the translocation of individuals between populations should consider environmental stress as a risk factor.1. 近交衰退（inbreeding depression, ID）、远交衰退（outbreeding depression, OD）与杂种优势（heterosis）可在植物种群中同时发生。环境胁迫下近交衰退通常会加剧，但近交、种群间远交与干旱这类环境胁迫对植物表现及植食性昆虫抗性的综合效应仍不明晰。 2. 为明确依赖于环境与家系的近交衰退、远交衰退及杂种优势，我们以5个种群的黑芥（Brassica nigra）为材料开展同质园实验。将自交家系、种群内远交家系及种群间远交家系分别置于干旱环境与正常水分条件下。记录了三类取食功能群迥异的专食性植食者的种群丰度与造成的取食损伤：分别为韧皮部取食的甘蓝蚜（Brevicoryne brassicae）、叶食性的油菜蓝跳甲（Psylliodes chrysocephalus）以及蛀茎性的四齿根瘤象幼虫（Ceutorhynchus quadridens）。 3. 干旱胁迫对植物生长、植食性昆虫抗性及抗甘蓝蚜能力产生负面影响，却对繁殖投入与植物次生代谢物黑芥子苷（sinigrin）的积累产生正向效应。本研究发现干旱胁迫诱导了株高与繁殖投入相关的杂种优势丧失。相较于种群内远交植株，种群间远交植株的地上生物量对干旱胁迫更为敏感。 4. 干旱胁迫与近交可协同负向影响生长及繁殖相关性状（即依赖于环境的近交衰退，environment-dependent inbreeding depression, EDID）。种群内不同家系间的近交衰退与依赖于环境的近交衰退程度存在显著变异。依赖于环境的近交衰退的遗传变异可缓冲与生境破碎化及伴随的环境胁迫相关的遗传压力。若要全面解析胁迫条件下近交与种群间远交的综合效应，需考虑近交与种群间远交效应的不同空间尺度。 5. 综合与结论。本研究结果表明，干旱胁迫不仅影响近交衰退（ID），还会调控杂种优势。这些发现为人为环境变化与生境破碎化的遗传效应对植物及其与其他生物互作的综合影响提供了新的研究视角。旨在通过种群间个体迁殖恢复遗传退化种群的保护计划，应将环境胁迫视为一项风险因子。