Evolutionary deja vu. A case of convergent evolution in an ant-plant association. Myrmelachista, Brachymyrmex, and Lasius ants

Obligatory ant-plant symbioses often appear to be single evolutionaryshifts within particular ant lineages; however, convergence can be revealedonce natural history observations are complemented with molecularphylogenetics. Here, we describe a remarkable example of convergentevolution in an ant-plant symbiotic system. Exclusively arboreal,Myrmelachista species can be generalized opportunists nesting in severalplant species or obligately symbiotic, live-stem nesters of a narrow set ofplant species. Instances of specialization within Myrmelachista are knownfrom northern South America and throughout Middle America. In MiddleAmerica, a diverse radiation of specialists occupies understory treeletsof lowland rainforests. The morphological and behavioural uniformityof specialists suggests that they form a monophyletic assemblage,diversifying after a single origin of specialization. Using ultraconservedelement phylogenomics and ancestral state reconstructions (ASRs), weshow that shifts from opportunistic to obligately symbiotic evolvedindependently in South and Middle America. Furthermore, our analysessupport a remarkable case of convergence within the Middle Americanradiation, with two independently evolved specialist clades, arising nearlysimultaneously from putative opportunistic ancestors during the latePliocene. This repeated evolution of a complex phenotype suggests similarmechanisms behind trait shifts from opportunists to specialists, generatingfurther questions about the selective forces driving specialization.