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Oak galls exhibit ant-dispersal convergent with myrmecochorous seeds

Citation

Warren, Robert et al. (2022), Oak galls exhibit ant-dispersal convergent with myrmecochorous seeds , Dryad, Dataset, https://doi.org/10.5061/dryad.9ghx3ffk2

Abstract

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.