Nicholls James A, Melika George, Stone Graham N
Am Nat. 2017 Jan;189(1):67-77. doi: 10.1086/689399. Epub 2016 Nov 2.
Many herbivores employ reward-based mutualisms with ants to gain protection from natural enemies. We examine the evolutionary dynamics of a tetra-trophic interaction in which gall wasp herbivores induce their host oaks to produce nectar-secreting galls, which attract ants that provide protection from parasitoids. We show that, consistent with other gall defensive traits, nectar secretion has evolved repeatedly across the oak gall wasp tribe and also within a single genus (Disholcaspis) that includes many nectar-inducing species. Once evolved, nectar secretion is never lost in Disholcaspis, consistent with high defensive value of this trait. We also show that evolution of nectar secretion is correlated with a transition from solitary to aggregated oviposition, resulting in clustered nectar-secreting galls, which produce a resource that ants can more easily monopolize. Such clustering is commonly seen in ant guard mutualisms. We suggest that correlated evolution between maternal oviposition and larval nectar induction traits has enhanced the effectiveness of this gall defense strategy.
许多食草动物与蚂蚁建立基于奖励的互利共生关系，以获得免受天敌侵害的保护。我们研究了一种四营养级相互作用的进化动态，其中瘿蜂食草动物诱导其宿主橡树产生分泌花蜜的虫瘿，这些虫瘿吸引蚂蚁，蚂蚁提供免受寄生蜂侵害的保护。我们发现，与其他瘿防御特征一致，花蜜分泌在橡树瘿蜂部落中反复进化，在一个包括许多诱导花蜜的物种的单一属（Disholcaspis）中也有进化。一旦进化，花蜜分泌在Disholcaspis中就不会消失，这与该特征的高防御价值一致。我们还表明，花蜜分泌的进化与从单独产卵到聚集产卵的转变相关，导致分泌花蜜的虫瘿聚集，产生一种蚂蚁可以更容易垄断的资源。这种聚集在蚂蚁保护互利共生关系中很常见。我们认为，母体产卵和幼虫花蜜诱导特征之间的协同进化增强了这种瘿防御策略的有效性。
