ALLOMERUS
Molecular and chemical ecology of a tripartite association plant-ant-fungus
[ANR Jeunes Chercheurs Program 2006]
The ubiquity and ecological dominance of ants make them a favoured target of mutualisms. Protective ant-plant mutualisms are always characterized by horizontal transmission, which poses several adaptive problems, such as ant queens finding a host or the exploitation of the mutualism by parasites and cheaters. A possible evolutionary answer to such invasions by non-mutualistic organisms depends on the existence of selective sieves to let filter through the best partners.
We are developing an interdisciplinary research program combining field studies and genetic and chemical analyses in order to obtain a fully comprehensive view of a novel tripartite system between an ant species, a plant and a sooty mould. Our objectives are the study of (i) the nature and roles of selective filters in the observed pattern of association and evolutionary ecology of this ant-plant association; (ii) the nature of the association between the ant and the sooty mould; and (iii) the spatial population genetic structure of the three partners to infer the transmission modes of these associations.
Model system
Hirtella physophora (Chrysobalanaceae) is an ant-plant found in the Amazonian understorey and exclusively inhabited in French Guiana by the ant Allomerus decemarticulatus (Myrmicinae). The plant houses ant colonies in pouches situated at the base of the leaf lamina and furnishes them with extrafloral nectar in exchange for protection from herbivory.
The Allomerus also build galleried structures on their host plant’s stems to trap much larger insects. Allomerus workers hide in the galleries with their heads just under the holes, mandibles wide open, waiting for an insect to land. To construct the galleries, workers begin by cutting the trichomes along the sections of plant stems and bind them together. Later, this structure is reinforced by the mycelium of a sooty mould manipulated by the ants that serves as a more permanent binding material.
