Abstract：
Obligatory ant-plant symbioses often appear to be single evolutionary shifts within particular ant lineages; however, convergence can be revealed once natural history observations are complemented with molecular phylogenetics. Here, we describe a remarkable example of convergent evolution in an ant-plant symbiotic system. Exclusively arboreal, Myrmelachista species can be generalized opportunists nesting in several plant species or obligately symbiotic, live-stem nesters of a narrow set of plant species. Instances of specialization within Myrmelachista are known from northern South America and throughout Middle America. In Middle America, a diverse radiation of specialists occupies understory treelets of lowland rainforests. The morphological and behavioural uniformity of specialists suggests that they form a monophyletic assemblage, diversifying after a single origin of specialization. Using ultraconserved element phylogenomics and ancestral state reconstructions, we show that shifts from opportunistic to obligately symbiotic evolved independently in South and Middle America. Furthermore, our analyses support a remarkable case of convergence within the Middle American radiation, with two independently evolved specialist clades, arising nearly simultaneously from putative opportunistic ancestors during the late Pliocene. This repeated evolution of a complex phenotype suggests similar mechanisms behind trait shifts from opportunists to specialists, generating further questions about the selective forces driving specialization.
摘要：
强制性蚂蚁-植物共生通常似乎是特定蚂蚁谱系内的单一进化转变；然而，一旦自然史观察得到分子系统发育的补充，就可以揭示收敛。这里,我们描述了在蚂蚁-植物共生系统中趋同进化的一个显著例子。独家树栖，Myrmelachista物种可以是在几种植物物种中筑巢或强制共生的广义机会主义者，一组狭窄的植物物种的活茎巢。从南美北部和整个中美洲都知道Myrmelachista中的专业化实例。在中美洲，各种各样的专家辐射占据了低地雨林的林下小树。专家的形态和行为一致性表明它们形成了单系组合，在单一专业化起源后实现多元化。使用超保守元素系统基因组学和祖先状态重建，我们表明，从机会主义到强制性共生的转变是在南美和中美洲独立进化的。此外，我们的分析支持了一个显著的中美洲辐射趋同的案例，有两个独立进化的专家分支，几乎同时产生于上新世晚期推定的机会主义祖先。复杂表型的这种重复进化表明，从机会主义者到专家的特质转变背后的类似机制，产生关于推动专业化的选择性力量的进一步问题。
