An ant symbiont directly and indirectly limits its host plant’s reproductive success
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In theory, mutualisms are intrinsically unstable, and the search for the maximum profit at the minimum cost should lead every mutualist to become a parasite. From an empirical point of view, mutualisms are ubiquitous and of major importance to ecosystems, suggesting the existence of mechanisms that enhance the maintenance of such relationships. We focused on the obligatory myrmecophytic association between the Neotropical plant Hirtella physophora (Chrysobalanaceae) and the ant Allomerus decemarticulatus (Myrmicinae). The plant shelters the ants in leaf pouches in exchange for protection from phytophagous insects. We experimentally demonstrated that the ants partially castrate their host plant by destroying almost two-thirds of its floral buds. The ants also impede pollination through their presence and interactions with pollinators. These results reveal that ant activity negatively affects the plant’s reproduction both directly and indirectly. This dual negative effect does not result in the complete castration of the plant. We also highlight major limitations to plant reproduction due to the spontaneous abscission of flowers and to the limited quantity and/or poor quality of the pollen. These limitations must not be overlooked since they can alter the outcome of the association of H. physophora with its ant partner. We therefore conclude that the evolutionary fate of the relationship depends on both ant castration intensity and obstacles to plant fertilization not related to the presence of ants.
KeywordsEvolutionary conflict Cheater Pollination Mutualism breakdown Myrmecophyte
We are grateful to the Laboratoire Environnement de Petit Saut for furnishing logistical help, to Isabelle Henry for her help in the field, to Jean-Baptiste Ferdy for statistical help and to Andrea Yockey-Dejean for editing the manuscript. Financial support for this study was provided by a research program of the French Agence Nationale de la Recherche (research agreement n°ANR-06-JCJC-0109-01), by the ESF-EUROCORES/TECT/BIOCONTRACT program, by the Programme Convergence 2007-2013 Région Guyane from the European Community (Project DEGA), and by the Programme Amazonie II of the French Centre National de la Recherche Scientifique (Project 2ID).
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