Symbiodiniaceae is a diverse group of dinoflagellates that form symbioses with marine invertebrates, provisioning energy and nutrients for their hosts. Symbiont diversity is a well-known predictor of host fitness and stress tolerance. Yet, we have a limited understanding of the mechanisms by which in hospite symbiont communities are structured. Therefore, we hypothesized that phylogenetic differences in nitrogen assimilation may affect symbiont dominance, as has been demonstrated in phytoplankton communities. Here, we quantified species-specific rates of nitrate assimilation using stable isotope labeling, and investigated key traits that have been adopted in phytoplankton ecology to explain the fundamental concept of nitrogen acquisition strategies and size-related trade-offs in Symbiodiniaceae. Traits related to structure and function were measured to look for convergent ecological strategies. Despite the limited sample size, we could distinguish two groups among the five species of Symbiodiniaceae with features described by the phytoplankton’s competition theories for resources: the affinity-adapted species which were associated with larger size, higher nitrogen content and nitrate affinity; and the velocity-adapted species which were small size, efficient in maximum nitrate assimilation, specific carbon assimilation rate, and growth. Our work supports the relevance of a functional trait-based approach to describe Symbiodinaceae diversity. The two contrasting nitrogen acquisition strategies identified may be fundamental to explain the composition and dynamics of Symbiodinaceae in hospite, stressing the importance of bottom-up mechanisms in shaping symbiont composition.

中文翻译：

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对共生科养分获取策略的基于性状的理解

Symbiodiniaceae 是一组多样化的甲藻，它们与海洋无脊椎动物形成共生关系，为其宿主提供能量和营养。共生体多样性是宿主健康和压力耐受性的众所周知的预测因子。然而，我们对寄宿共生社区的结构机制了解有限。因此，我们假设氮同化的系统发育差异可能会影响共生体的优势，正如在浮游植物群落中所证明的那样。在这里，我们使用稳定同位素标记量化了特定物种的硝酸盐同化率，并研究了浮游植物生态学中采用的关键特征，以解释共生科中氮获取策略和大小相关权衡的基本概念。测量与结构和功能相关的特征以寻找趋同的生态策略。尽管样本量有限，但我们可以根据浮游植物的资源竞争理论描述的特征，在共生科的 5 种物种中区分出两组：亲和适应物种与较大的体型、较高的氮含量和硝酸盐亲和力相关；和速度适应的物种，它们体积小，在最大硝酸盐同化、特定碳同化速率和生长方面是有效的。我们的工作支持基于功能性状的方法来描述共生科多样性的相关性。确定的两种截然不同的氮获取策略可能是解释寄宿家庭共生菌科的组成和动态的基础，