“Ants at plant wounds – a little-known trophic interaction with evolutionary implications for ant-plant interactions”

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Michael Staab, Felix Fornoff, Alexandra-Maria Klein, and Nico Blüthgen

Ants visiting plant wounds may have stimulated the evolution of extrafloral nectaries

Polyrhachis dives, the ant species most commonly observed on plant wounds, on a Castanea henryi leaf.
(From figure 1 of Staab et al., © 2017 The University of Chicago Press)

Abstract

Extrafloral nectaries (EFNs) allow plants to engage in mutualisms with ants preventing herbivory in exchange for food. EFNs occur scattered through the plant phylogeny and likely evolved independently from herbivore-created wounds subsequently visited by ants collecting leaked sap. Records of wound-feeding ants are, however, anecdotal. By surveying 38,000 trees from 40 species, we conduct the first quantitative ecological study of this overlooked behavior. Ant-wound interactions were widespread (0.5% of tree individuals) and occurred on 23 tree species. Interaction networks were opportunistic, closely resembling ant-EFNs networks. Fagaceae, a family lacking EFNs, were strongly overrepresented. For Fagaceae, ant occurrence at wounds correlated with species-level leaf damage, potentially indicating that wounds may attract mutualistic ants, supporting the hypothesis of ant-tended wounds as precursors of ant-EFNs mutualisms. Given the commonness of herbivore wounds, wound sap as steadily available food source might furthermore help to explain the overwhelming abundance of ants in (sub)tropical forest canopies. Read the Article