Oak galls exhibit ant-dispersal convergent with myrmecochorous seeds

Ants disperse oak galls of some cynipid wasp species similarly to how they disperse seeds with elaiosomes. We conducted choice assays in field and lab settings, with ant-dispersed seeds and wasp-induced galls found in ant nests and found that seed-dispersing ants retrieve these galls as they do myrmecochorous seeds. We also conducted manipulative experiments in which we removed the putative ant-attracting appendages (“kapéllos”) from galls and found ants are specifically attracted to kapéllos. Finally, we compared chemical composition and the histology of ant-attracting appendages on seeds and galls, and they both had similar fatty-acid compositions as well as morphology. We also observed seed-dispersing ants retrieve oak galls to their nests, and rodents and birds consuming oak galls that were not retrieved by ants. These results suggest convergence in ant-mediated dispersal between myrmecochorous seeds and oak galls. Based on our observations, a protective advantage for galls retrieved to ant nests seems a more likely benefit than dispersal distance, as also has been suggested for myrmecochorous seeds. These results require reconsideration of established ant-plant research assumptions as ant-mediated seed and gall dispersal appear strongly convergent and galls may be far more abundant in eastern North American deciduous forests than myrmecochorous seeds.