Should we sync? Seascape-level genetic and ecological factors determine seagrass flowering patterns [dataset]

Spatial and temporal heterogeneity in flowering occur in many plant species with abiotic pollination and may confer fitness advantages through mechanisms such as predator satiation or pollination efficiency. Environmental factors such as light quality or quantity and temperature play an important role in inducing synchronisation on wide geographic scales. On a smaller geographic scale, external factors such as resource availability and herbivory are theorised to trigger flowering, while genetic factors may also play an important role. In this study, we assessed the importance of ecological and genetic factors in shaping seascape-level spatial heterogeneity in flowering of the seagrass Posidonia oceanica. By investigating spatially close sites ( 20 km) with similar seascape configurations and depth, we assume that major environmental drivers (temperature and light) were equivalent. We assessed four ecological factors (productivity, leaf nitrogen and carbon content and herbivory) and three genetic factors (heterozygosity, relatedness and clonality) to assess three hypotheses for synchronised flowering in P. oceanica: (1) clone synchronisation (internal clock hypothesis), (2) variation in nutrient availability, potentially caused by spatial heterogeneity in herbivory rates or nutrient translocation via clonal integration (resource budget hypothesis) or (3) kin selection and sibling synchronisation. Internal relatedness and heterozygosity had a significant positive effect on the abundance of flowers. Moreover, productivity and genotypic richness (clonality) were negatively associated with flower density, although at a lower level of significance. In addition we found that clones were almost exclusively shared among mass-flowering patches and patches without mass-flowering, respectively. Synthesis. The results shed new light on seagrass flowering patterns and on the mechanisms of flower synchronisation at the patch level within a wider spatial scale. We found support for the kin selection hypothesis and indirect evidence for the resource budget hypothesis. Thus a combination of mainly genetic but also ecological factors causes the observed heterogeneous flowering patterns in Posidonia oceanica seascapes. In addition, we found a strong positive relationship between the number of flowers and heterozygosity, adding evidence to the controversial association between heterozygosity and fitness when a limited number of loci are used. To our knowledge, this study is the first to link both ecological and genetic factors with flower abundance in a species with a presumed masting strategy.

许多非生物传粉（abiotic pollination）的植物类群均存在开花的时空异质性，该特性可通过捕食者饱和效应（predator satiation）或提升传粉效率等机制赋予植株适合度优势（fitness advantage）。在大地理尺度上，光照质量、光照强度与温度等环境因子在诱导开花同步性方面发挥重要作用。而在较小地理尺度下，资源可获得性、植食作用（herbivory）等外源因子被理论认为可触发开花，遗传因子同样可能发挥关键作用。
本研究旨在评估生态与遗传因子在塑造波西多尼亚海草（Posidonia oceanica）开花的海景观尺度（seascape-level）空间异质性中的重要性。通过选取空间距离在20千米以内、海景观配置与水深相似的样地开展调查，本研究假设各采样点的主要环境驱动因子（温度与光照）保持一致。本研究共评估四类生态因子（生产力、叶片氮与碳含量以及植食作用）与三类遗传因子（杂合性（heterozygosity）、亲缘关系（relatedness）以及克隆性（clonality）），旨在验证关于波西多尼亚海草开花同步性的三项假说：（1）克隆同步假说（内源性生物钟假说）；（2）养分可获得性变异假说——该变异可能由植食作用速率的空间异质性或通过克隆整合实现的养分转运所引发（资源预算假说）；（3）亲缘选择（kin selection）与同胞同步假说。
研究结果显示，亲缘关系与杂合性对开花数量具有显著的正向影响。此外，生产力与基因型丰富度（克隆性）与开花密度呈负相关关系，尽管该关联的显著性水平较低。我们还发现，克隆株系几乎仅分别出现在大规模开花斑块与未大规模开花的斑块中。
综合分析。本研究结果为海草开花模式以及更大空间尺度下斑块级别的开花同步机制提供了新的认识。本研究为亲缘选择假说提供了支持证据，同时为资源预算假说提供了间接佐证。由此可见，主要由遗传因子辅以生态因子共同作用，造就了波西多尼亚海草海景观中观测到的异质性开花模式。此外，本研究发现开花数量与杂合性之间存在显著正相关关系，为"当使用有限数量的基因座（locus，复数为loci）时，杂合性与适合度之间存在争议性关联"这一观点补充了证据。据我们所知，本研究首次将生态与遗传因子与具有假定结实同步策略（masting strategy）的物种的开花数量关联起来。