Every organism on Earth must cope with a multitude of species interactions both directly and indirectly throughout its life cycle. However, how selection from multiple species occupying different trophic levels affects diffuse mutualisms has received little attention. As a result, how a given species amalgamates the combined effects of selection from multiple mutualists and antagonists to enhance its own fitness remains little understood. We investigated how multispecies interactions (frugivorous birds, ants, fruit flies and parasitoid wasps) generate selection on fruit traits in a seed dispersal mutualism. We used structural equation models to assess whether seed dispersers (frugivorous birds and ants) exerted phenotypic selection on fruit and seed traits in the spiny hackberry (Celtis ehrenbergiana), a fleshy‐fruited tree, and how these selection regimes were influenced by fruit fly infestation and wasp parasitoidism levels. Birds exerted negative correlational selection on the combination of fruit crop size and mean seed weight, favouring either large crops with small seeds or small crops with large seeds. Parasitoids selected plants with higher fruit fly infestation levels, and fruit flies exerted positive directional selection on fruit size, which was positively correlated with seed weight. Therefore, higher parasitoidism indirectly correlated with higher plant fitness through increased bird fruit removal. In addition, ants exerted negative directional selection on mean seed weight. Our results show that strong selection on phenotypic traits may still arise in perceived diffuse species interactions. Overall, we emphasize the need to consider diverse direct and indirect partners to achieve a better understanding of the mechanisms driving phenotypic trait evolution in multispecies interactions.

中文翻译：

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果实性状的选择是由食果鸟类、果蝇、寄生蜂和种子传播蚂蚁之间的相互作用介导的

地球上的每一个生物都必须在其整个生命周期中直接和间接地应对多种物种相互作用。然而，从占据不同营养级别的多个物种中进行的选择如何影响弥散共生很少受到关注。因此，一个给定的物种如何结合来自多个互惠者和拮抗者的选择的综合影响来增强其自身的适应度仍然知之甚少。我们研究了多物种相互作用（食果鸟类、蚂蚁、果蝇和寄生蜂）如何在种子传播共生中产生对果实性状的选择。我们使用结构方程模型来评估种子传播者（食果鸟类和蚂蚁）是否对多刺朴树莓（Celtis ehrenbergiana）（一种肉质果树）的果实和种子性状进行表型选择，以及这些选择制度如何受到果蝇侵扰和黄蜂寄生水平的影响。鸟类对果实作物大小和平均种子重量的组合施加负相关选择，有利于具有小种子的大作物或具有大种子的小作物。寄生蜂选择果蝇侵染水平较高的植物，果蝇对果实大小施加正向选择，这与种子重量呈正相关。因此，较高的寄生性与较高的植物适应性通过增加鸟类果实去除率间接相关。此外，蚂蚁对平均种子重量施加负向选择。我们的结果表明，在感知到的扩散物种相互作用中可能仍然会出现对表型性状的强烈选择。全面的，