Many epiphytic plants have associated with ants to gain nutrients. Here, we report a novel type of ant–plant symbiosis in Fiji where one ant species actively and exclusively plants the seeds and fertilizes the seedlings of six species of Squamellaria (Rubiaceae). Comparison with related facultative ant plants suggests that such farming plays a key role in mutualism stability by mitigating the critical re-establishment step.
We thank J. Aroles for essential help in the field and critical reading of the manuscript; A. Naikatini and M. Tuiwava for help with permissions and voucher collection; V. Mayer, University of Vienna, for instructions and material for the nitrogen isotope experiments; C. Mayr, University of Munich, for the analyses of nitrogen isotope ratios; M. Lehman, Metabolomic facility of the University of Munich (LMU), for the metabolomic analyses; E. Kaufmann and M. Janda for Philidris samples and for discussion; P.I. Garcia, G. Fisher and E. Economo for help with ant identification, P. S. Ward, C.S. Moreau, M. Jebb, A. Wistuba, and D. McKey for discussion; and M. Frederickson, N. Pierce, R. Ricklefs, A. B. F. Ivens and two anonymous reviewers for comments on the manuscript. This work was supported by a grant from the German Research Foundation (DFG), RE 603/20, and grants from the Society of Systematic Biologists and the American Association of Plant Taxonomy to G.C.
Species S. imberbis (Vanua Levu) replicate.