La fonction myrmécophile de Cecropia obtusa Trecul (Cecropiaceae) en Guyane française

Abstract

Summary Cecropia obtusa Trecul is a myrmecophytic plant associated in a strict relation with the ants Azteca (A. alfari Emery and A. traili Emery). The ants inhabit the internodes of the tree and feed on nutritive bodies or müllerian bodies. These multicellular corpuscles are produced on the abaxial face of the base of the petiole. This région is covered with a velutinous mat of multicellular but uniseried trichomes called trichilium. The production activity of müllerian bodies and the activity of the ants are synchronous: three hours before the sundown. A Phycitinae caterpillar may occupy the Cecropia internodes and consumes müllerian bodies exclusively. A fungus, Fusarium moniliforme, grows on the trichilium in the absence of ants. The distribution of Cecropia obtusa is homogeneous in space and time but its growth is under control of topographic, edaphic and climatic factors. The comparison between trees occupied by ants and inoccupied ones shows that these last ones grow less quickly and that the müllerian production is smaller. Cecropia trees cultivated in greenhouse show the same behaviour than inoccupied ones in the field with, however, a greater production rate of müllerian bodies. When caterpillars inhabit the plant the production of müllerian bodies is higher than in the case of inoccupied Cecropia. The part of ants and caterpillars in the plant growth and müllerian bodies production is discussed. The partial chimical analyze of food bodies shows a clear dominance of glycogen which add simple sugars, lipids, proteins and C and E vitamins. The differences between the guiana food bodies and müllerian bodies producted in greenhouse are discussed. The histological and cytological studies of müllerian body place in a prominent position its development and the origin of the principal synthetized substances which have a trophic part for ants and caterpillars.