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Ants Disperse Oak Leaf Galls Just Like Herbaceous Seeds

Speaker: Dr. Robert Warren II, SUNY Buffalo State College

That some ants will disperse herbaceous seeds with elaiosomes (fatty acid appendages that attract ants) was first reported in 1906. However, a parallel process, in which the same ants collect and disperse oak leaf galls, has gone undetected. As it turns out, ants disperse oak galls (induced by cynipid wasp species) very similarly to how they disperse seeds. 

Indeed, (i) choice assays in field and laboratory settings showed that seed-dispersing ants prefer and retrieve wasp-induced galls as they do the seeds of ant-dispersed plants (myrmecochores); (ii) manipulative experiments in which the putative ant-attracting appendage (kapéllo) was removed from the galls showed that ants are specifically attracted to kapéllos (as they are elaiosomes on ant-dispersed seeds); (iii) the chemical composition and histology of ant-attracting appendages on seeds and galls have similar fatty acid compositions as well as morphology and (iv) oak galls not retrieved to ant nests were consumed by rodents and birds. 

These results suggest convergence in ant-mediated dispersal between myrmecochorous seeds and oak galls. A protective advantage for galls retrieved to ant nests seems a more likely benefit than dispersal distance, as has also 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 oak galls may be far more abundant in eastern North American deciduous forests than myrmecochorous seeds.