Plasticity of floral sex allocation within inflorescences of hermaphrodite Aconitum gymnandrum

Aims Sex allocation in plants is often plastic, enabling individuals to adjust to variable environments. However, the predicted male-biased sex allocation in response to low resource conditions has rarely been experimentally tested in hermaphroditic plants. In particular, it is unknown whether distal flowers in linear inflorescences show a larger shift to male allocation relative to basal flowers when resources are reduced. In this study, we measure position-dependent plasticity of floral sex allocation within racemes of Aconitum gymnandrum in response to reduced resource availability.Methods Using a defoliation treatment in the field applied to potted plants from a nested half-sibling design, we examined the effects of the treatment, flower position, family and their interactions.Important findings Allocation to male function increased with more distal flower position, while female allocation either did not change with position or declined at the most distal flowers. Defoliation significantly reduced the mass of both the androecium and gynoecium, but not anther number or carpel number. Gynoecial mass declined more strongly with defoliation than did androecial mass, resulting in a significant increase in the androecium/gynoecium ratio as predicted by sex allocation theory. Plastic responses of androecium mass and gynoecium mass were affected by flower position, with less mass lost in basal flowers, but similar plastic magnitude in both sexual traits across flower position lead to consistent variation in the androecium/gynoecium ratio along the inflorescence. A significant treatment*paternal family interaction for the androecium/gynoecium ratio is evidence for additive genetic variation for plastic floral sex allocation, which means that further evolution of allocation can occur.     

Size-dependent sex allocation in Aconitum gymnandrum (Ranunculaceae): physiological basis and effects of maternal family and environment

Theory predicts size-dependent sex allocation (SDS): flowers on plants with a high-resource status should have larger investment in females than plants with a low-resource status. Through a pot experiment with Aconitum gymnandrum (Ranunculaceae) in the field, we examined the relationship between sex allocation of individual flowers and plant size for different maternal families under different environmental conditions. We also determined the physiological base of variations in plant size. Our results support the prediction of SDS, and show that female-biased allocation with plant size is consistent under different environmental conditions. Negative correlations within families showed a plastic response of sex allocation to plant size. Negative genetic correlations between sex allocation and plant size at the family level indicate a genetic cause of the SDS pattern, although genetic correlation was influenced by environmental factors. Hence, the size-dependency of sex allocation in this species had both plastic and genetic causes. Furthermore, genotypes that grew large also had higher assimilation ability, thus showing a physiological basis for SDS.     

Phytochemical Evidence Related to the Phylogeny of Aconitum gymnandrum Maxim.

From the whole plant of Aconitum gymnandrum Maxim., four diterpene alkaloids have been isolated and identified: talatizamine, 14-acetyltalatizamine, condelphine and isotalatizidine. Thus the species nvestigated, belonging to the monotypic subgenus Gymnaconitum (Stapf) Rapaics, secms to be phytochemically closely related to A. nemorum M. Pop. and A. talassicum M. Pop. From the phytochemical point of view however, A. gymnandrum does not seem to be the most advanced species within the genus Aconitum.     

Insect and wind pollination of an alpine biennial Aconitum gymnandrum (Ranunculaceae)

Wind pollination can provide reproductive insurance for animal‐pollinated dioecious plants in the absence of available pollinators, but combinations of insect and wind pollination (ambophily) have rarely been studied in hermaphrodite herbs. We examined the stable occurrence of insect pollination and wind pollination over 4 years in a population of a biennial Aconitum species (A. gymnandrum) with actinomorphic and degenerate sepals. The total frequency of visits of two bumblebee species showed no distinct fluctuations in the studied population among the 4 years. However, seed production of netted flowers after emasculation indicated wind pollination had occurred. The seed number of bagged flowers with one visit by bumblebees was significantly less than that of netted flowers after one visit, or in control flowers. Both seed number and fruit set of netted flowers were significantly lower than in control flowers. These results suggest that wind pollination provides supplementary pollen to unvisited and/or once‐visited flowers, but accounts for only a small amount of seed production compared to bumblebee pollination in natural conditions. Such a combination of insect and wind pollination might play an important role in maintaining sexual reproduction of this biennial herb, allowing it to persist in arid habitats on the Qinghai‐Tibetan Plateau, especially during Quaternary glacial periods when pollinator populations oscillated extensively.     

露蕊乌头(毛茛科)不同海拔居群的传粉生态学

对青藏高原东北部两个不同海拔地点（互助,2460m和海北,3200m）的露蕊乌头Aconitum gymnandrum的传粉生态学进行了比较研究。研究结果表明高海拔居群的单花花期、雄性期持续时间、雌性期持续时间比低海拔长。露蕊乌头不存在无融合生殖现象,尽管高度自交亲和,但产生种子必须依赖传粉媒介。熊蜂是露蕊乌头的主要传粉昆虫,两个居群均存在传粉限制。熊蜂取食花蜜为主,在同一个花序上的访问顺序以由下向上为主,但在互助居群和海北居群有3．9％和2．7％的访花是由上向下进行的。统计发现有37．7％和29．3％的访问行为发生在同一植株内;因此,同株异花传粉造成的自交在露蕊乌头中仍然不能避免。低海拔居群的熊蜂种类和访花频率均高于高海拔居群,但自然状态下两个居群的结实率并没有显著差异。高海拔露蕊乌头居群可能具有较长的柱头持续时间,从而补偿了由于访花频率低带来的结实率降低。     

雌雄异熟植物露蕊乌头开花时间对雌雄功能期及表型性别的影响

开花时间决定了植物雌雄功能的交配机会, 最终影响繁殖成功。交配环境假说认为雌雄异熟植物开花时间的差异能引起植物表型性别的变异, 改变种群内的交配环境, 影响植物对雌雄功能的最佳性分配。为了研究开花时间对雌雄异熟植物的雌雄性别时期及表型性别的影响, 本文以毛茛科雄性先熟植物露蕊乌头(Aconitum gymnandrum)为实验材料, 记录了雄性和雌性功能期, 分析了植株开花时间、花的雌雄功能期和表型性别的关系。结果表明: 在植物同一花序内, 较晚开放的花有更长的雄性期和更短的雌性期, 性分配在时间上偏雄。雌雄功能期在时间上的相对分配随植物开花时间的变化表现出相似的趋势： 较晚开的花或较晚开花的个体, 花的雄性功能期相对于雌性功能期更长, 在时间上更偏向雄性功能。而且, 开花时间的差异影响种群内花的性比和植物个体的表型性别动态。随着开花时间由早到晚的变化, 种群内早期以雄花为主,末期以雌花为主, 种群内性别环境由偏雄向偏雌变化, 因此植株个体的平均表型性别则从偏雌转向偏雄。本文结果支持交配环境假说, 雄性先熟的露蕊乌头开花早期, 种群内花的性别比偏雄, 种群表型性别环境偏雄, 因而植物个体平均表型性别偏雌, 性别分配(即时间分配)偏向雌性功能, 而晚开花个体的平均性别偏雄, 更偏向雄性功能的分配。     

Variation of nectar production in relation to plant characteristics in protandrous Aconitum gymnandrum

Aims Floral nectar plays a vital role in plant reproductive success by attracting pollinators. Nectar traits of a flower can depend directly on plant characteristics other than environmental factors and exhibit extensive flower- and plant-level variations. Studies on nectar traits frequently focused on intraplant variation for dichogamous plants, but few have paid attention to both intra- and interplant nectar variations in relation to plant characteristics. Revealing within- and among-plant variation and its relative magnitude is important for our understanding of how pollinator-mediated selection can act on nectar traits and evolution of nectar traits.Methods Through investigating protandrous Aconitum gymnandrum populations at the Alpine Meadows and Wetland Ecosystems Research Station of Lanzhou University, we examined the relationships between nectar production per flower and plant characteristics (e.g. flower position within inflorescences, floral sexual phases, flowering time, inflorescence size and floral attractive traits).Important findings A. gymnandrum exhibited a declining gradient in the nectar volume along inflorescences, with more nectar in basal flowers than distal ones. Protandrous flowers of A. gymnandrum did not show gender-biased nectar production while the nectar volume varied with different stages of floral sexual phases. The significant correlation between the first flowering date of individuals and the mean nectar volume per flower was positive in 2013, but became negative in 2014, suggesting complex effects of biotic and abiotic factors. The mean nectar volume per flower was not related to inflorescence size (the number of total flowers per plant). Furthermore, nectar production was weakly associated with floral attractive traits (the petal width and the galea height), even if the effect of flowering time of individuals was removed, suggesting that the honesty of floral traits as signals of nectar reward for pollinators is not stable in this species.     

喜树花序内性别表达及性别分配

 花序内性别表达和性别分配的差异在被子植物中非常普遍。常见的变化模式是: 在顺次开放的花序内, 从早开的花到晚开的花, 生殖结构大小和数量依次减少, 晚开的花偏向雄性。通常认为资源竞争和位置效应是形成这种差异的主要原因。在喜树(Camptotheca acuminata)的聚伞花序内, 早开的头状花序在花序直径、小花直径、短雄蕊长度、坐果率、果序重量等方面与晚开的头状花序差异显著。通过去除喜树聚伞花序一级或一级和二级头状花序来控制花序内的资源分配, 从而分析影
响喜树花序内花性状、性别分配及生殖能力的主要因子。结果显示, 去除部分头状花序后, 剩余头状花序的花序直径、小花直径明显增加, 短雄蕊长度明显缩短, 位置间差异消失; 而坐果率、果序重量的位置间差异依然显著。表明资源限制对花序直径、小花直径和短雄蕊长度等影响显著, 而坐果率和果序重量受位置效应影响明显。喜树雄全同株的性别分配可能是对特定生殖状况和资源状况适应的结果。