Plant water limitation and its impact on the oviposition preferences of the monarch butterfly, Danaus plexippus (Lepidoptera: Nymphalidae)

Intensifying drought conditions across the western United States due to global climate change are altering plant-insect interactions. Specialist herbivores must find their host plants within a matrix of nonhosts, and thus often rely upon specific plant secondary chemistry for host location and oviposition cues. Climate-induced alterations to plant chemistry could thus affect female selection of larval food-plants. Here, we investigated whether host-plant water limitation influenced oviposition preference in a threatened invertebrate: the monarch butterfly (Danaus plexippus). We found that females deposited more eggs on reduced-water than on well-watered narrowleaf milkweed plants (Asclepias fascicularis), but we could not attribute this change to any specific change in plant chemistry. Specialist herbivores, such as the monarch butterfly, which are tightly linked to specific plant cues, may experience a shift in preferences under global-change conditions. Understanding oviposition prefe..., Seeds of A. fascicularis were collected from Reno, NV (39.49361, -119.85459) in 2018 and 2019 and germinated in May 2020. Plants were grown in 164 mL treepots with 50% peat moss: 34% vermiculite: 16% perlite. To manipulate water availability, soil saturation was maintained at 70% field capacity in control (well-watered) plants and at 30% in reduced-water plants for 1–3 weeks using a gravitational dry-down method following Diethelm et al. (2022). The variation in dry-down time is due to initially high dieback in the reduced-water group, which led us to add more plants to that treatment group, with the treatment maintained for 1 week. The 70% control level reflects what plants typically experience at agricultural field edges, whereas 30% represents a dry treatment that does not induce wilting (Diethelm et al. 2022). We avoided wilting because females may discriminate against wilted plants, independent of plant chemistry (Aikins et al. 2023). To allow female monarchs to select a mate, each..., Instrument- or software-specific information needed to interpret the data: -R Core Team (2023). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL https://www.R-project.org/.-RStudio (2023) URL http://www.rstudio.com/-Rstudio packages: tidyvers, ggplot, ggforce (for jitter plot), Hmisc, Rmisc (for SE summary), lmtest (for model comparisions), glmmTMB (for mixed models), MuMin, DHARMa, BBmisc, hillR, ggpubr全球气候变化导致美国西部干旱状况持续加剧，正改变着植物与昆虫的相互作用关系。专食性草食动物（specialist herbivores）需要在非寄主植物的群落矩阵中定位其寄主植物，因此通常依赖特定的植物次生化学物质作为寄主识别与产卵的线索。气候变化引发的植物化学组成改变，可能会影响雌性昆虫对幼虫食料植物的选择。 本研究以一种受威胁的无脊椎动物——黑脉金斑蝶（Danaus plexippus）为对象，探究寄主植物的水分限制是否会对其产卵偏好产生影响。我们发现，相较于浇水充足的窄叶马利筋（Asclepias fascicularis），雌性黑脉金斑蝶会在水分胁迫组的植株上产下更多卵，但无法将这一偏好变化归因于植物化学物质的某一特定改变。与特定植物线索紧密绑定的专食性草食动物（如黑脉金斑蝶），在全球变化的环境条件下可能会出现产卵偏好的偏移。对产卵偏好的了解…… 窄叶马利筋的种子于2018年和2019年从美国内华达州里诺市（39.49361, -119.85459）采集，并于2020年5月进行萌发。植株种植于164 mL的育苗盆中，培养基质配比为50%泥炭藓、34%蛭石、16%珍珠岩。为调控土壤水分可用性，参照Diethelm等人（2022）提出的重力干燥法，对照组（浇水充足）植株的土壤饱和度维持在田间持水量的70%，水分胁迫组维持在30%，处理时长为1至3周。干燥处理的时长存在差异，原因是水分胁迫组初期出现了较高比例的枯梢现象，因此我们向该处理组补充了更多植株，并将处理时长统一调整为1周。70%的对照水平反映了植株在农田边缘的典型生长水分条件，而30%的水平代表不会引发植株萎蔫的干旱处理（Diethelm et al. 2022）。本研究避免植株出现萎蔫，因为雌性昆虫可能会基于植物化学物质以外的因素对萎蔫植株产生排斥性选择（Aikins et al. 2023）。 为使雌性黑脉金斑蝶能够完成交配，每…… 用于解读本研究数据的仪器与软件专属信息如下： - R核心团队（2023）。《R：一种统计计算语言与环境》。奥地利维也纳统计计算R基金会。网址：https://www.R-project.org/ - RStudio（2023） 网址：http://www.rstudio.com/ - RStudio扩展包：tidyverse（原文笔误为tidyvers）、ggplot、ggforce（用于绘制抖动图）、Hmisc、Rmisc（用于标准误汇总）、lmtest（用于模型比较）、glmmTMB（用于构建混合效应模型）、MuMIn、DHARMa、BBmisc、hillR、ggpubr