Few studies investigated the phenotypic plasticity of extrafloral nectary (EFN) functioning associated with indirect plant defense across species. Here, we experimentally investigate in three sympatric legume species the role of EFNs, hypothesizing that plant species with larger EFNs have higher induced nectar secretion after herbivory events, greater control over secretion, and are more likely to interact with more protective ant partners. We targeted 30 individuals of each legume species and estimated EFN size and activity in the field. We conducted field experiments to evaluate the phenotypic plasticity of nectar production after leaf damage and censused ant species feeding on EFNs. Plant species increased nectar after leaf damage but in different ways. Supporting our hypothesis, C. duckeana, with the largest EFNs, increased all nectar descriptors, taking its place as the most productive and intense post-herbivory induced response, attracting more dominant ants than the other plant species. The higher control over reward production in plant species with larger-sized EFN reflects an induction mechanism under damage that reduces costs and increases the potential benefits of indirect biotic defences. Together, these plant traits shape the patterns of ant attendance and defence against herbivores, possibly favouring the maintenance of plant protection mutualisms widespread in nature.

The research was carried out in a ​​seasonally dry tropical forest area in the Caatinga domain, Vale do Curu Experimental Farm (3º48'43''S and 39º20'42''W, 80 m asl), municipality of Pentecoste, State of Ceará, Brazil. Three species of Chamaecrista native to the Brazilian northeastern semiarid region were selected: Chamaecrista diphylla (L.) (Fig. 1I-L); Chamaecrista duckeana (P. Bezerra & Afr. Fern.) H. S. Irwin & Barneby (Fig. 1M-R) and Chamaecrista calycioides (DC. ex Collad.) Greene. Field collection on the three Chamaecrista species was carried out between January and June of 2020. 

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