EntomoBrasilis 8 (2): 85-90 (2015) FórumResumo. Uma associação bem conhecida dentre as interações ecológicas é o mutualismo entre plantas do gênero Cecropia e formigas, na maioria das vezes pertencentes ao gênero Azteca. Nesta interação, as formigas nidificam nas domáceas presentes no tronco oco das mirmecófitas e se alimentam de recursos alimentares fornecidos pela planta, conhecidos como corpúsculos mullerianos. Em compensação, as formigas protegem a planta hospedeira contra o ataque de herbívoros e a invasão por trepadeiras, e nutrem-na através de resíduos abandonados no tronco. Entretanto, a efetividade desta associação pode variar em função de vários fatores, como por exemplo, a espécie de formiga associada e o tipo de habitat da planta mirmecófita. Cerca de 10% das espécies de Cecropia perderam suas características atrativas, como por exemplo, espécies que habitam ilhas e altas altitudes. Aspectos como a riqueza de formigas associadas e estudos moleculares evidenciam que a colonização destas plantas ocorreu diversas vezes e independentemente por alguns gêneros de formigas. A pressão de seleção exercida por algumas espécies de formigas pode ter sido um dos fatores decisivos para o desenvolvimento dos traços atrativos para as formigas em Cecropia. Com a evolução destas características as formigas puderam se tornar um parceiro efetivo da planta, facilitando a co-evolução de interações mais específicas. Palavras-chave:Associação; Benefícios; Co-evolução; Formigas; Mirmecófita. Plant-Insect Interactions: Biological and Ecological Aspects of Cecropia-Azteca MutualismAbstract. A well-known association is the mutualism between plants is between plant species of the genus Cecropia and ants, mostly belonging to the genus Azteca. In this association, the ants nest in domatia present in the hollow trunk of this myrmecophytes and feed on food bodies provided by the plant, known as mullerian bodies. In return, the ants protect the host plant against herbivore attacks and invasion by vines, and nourish it through waste laid in the trunk. However, the effectiveness of this association may vary with several factors, such as the associated ant species and the habitat type of the myrmecophyte. About 10% of Cecropia species lost their attractive characteristics, such as species living in high altitude and inhabit islands. Aspects like associated ant richness and molecular studies show that the colonization of these plants by ants occurred several times and independently by different genera. The selection pressure exerted by some species of ants may have been one of the decisive factors for the development of attractive traits for ants in Cecropia. With the evolution of these features ants might become an effective partner of the plant, facilitating the co-evolution of specific interactions.

Although the interactions (including mutualism) between Cecropia and numerous ants have been already well documented, biogeographic studies on the distribution patterns of Cecropia with its associated ants have never been conducted in northeast Brazil. This study evaluates: (1) the regional diversity of Cecropia spp. sheltering ants; (2) the diversity of the ants living in these trees; and (3) the species-specific relationships along a longitudinal east-west transect in southwest Bahia. The ants nesting at the apical stem of 521 Cecropia individuals, mostly C. pachystachya (Trécul 1847), were sampled; 437 trees were occupied by ants belonging to 40 species. The commonest ant species was Azteca alfari (Emery 1893). The abundance of Cecropia, as well as the relative frequency of tree occupation, ant diversity, and association between ant species, were higher at lower altitudes, where rainforest vegetation predominates. Cecropia proved to be an important nesting site for various ant species in this biotope.Résumé. Interactions entre Cecropia (Urticaceae) et les fourmis (Hymenoptera : Formicidae) le long d'un transect longitudinal est-ouest dans le Nord-est du Brésil. Bien que les interactions (dont le mutualisme) entre Cecropia et de nombreuses fourmis aient déjà été bien documentées, aucune étude biogéographique portant sur les modèles de distribution de Cecropia et de ses fourmis associées n'a été menée jusqu'à présent dans le Nord-Est du Brésil. Cette étude évalue : 1) la diversité régionale de Cecropia spp. abritant des fourmis ; 2) la diversité des fourmis qui vivent dans ces arbres ; et 3) la relation de spécificité qui existe dans ces relations le long d'un transect longitudal est-ouest situé dans le sud de Bahia (Brésil). Nous avons échantillonné les fourmis des rameaux apicaux de 521 Cecropia, principalement C. pachystachya (Trécul 1847); 437 arbres étaient occupés par 40 espèces de fourmis. La fourmi la plus fréquente était Azteca alfari (Emery 1893). L'abondance de Cecropia, ainsi que la fréquence relative de l'occupation de l'arbre, la diversité des fourmis et les associations entre espèces de fourmis, étaient plus élevées à basse altitude où la végétation prédominante est du type forêt tropicale. Cecropia est donc un important site de nidification pour de nombreuses espèces de fourmis dans ce biotope.