O papel das galhas intermediando interações em um sistema multitrófico

Abstract

The galling habit probably was selected by the obtainment of adaptive advantages such as specific substance allocation (nutritional hypothesis), microclimatic stability and protection against natural enemy attack (enemy hypothesis). Galling insects modify the host tissue structure and physiology, and the gall development depends on the galling specific stimulus. Thus, the entry of natural enemies into the system can provoke structural and chemical changes in the gall and consequently, decrease the fitness of the galling. Our study system Palaeomystella oligophaga (Lepidoptera) - Macairea radula (Melastomataceae) showed conspicuous galls, with thick and rigid parenchyma, covered by projections with trichomes, and show a gradient of green to red colorations. Despite these characteristics, they are inserted in a multitrophic context, where the gallings are attacked directly or indirectly by different species of insects. Herein, we investigate the importance of gall traits mediating these interactions, and how these organisms affect their metabolism, which may reveal the true role of the gall as an intermediary of galling-enemy interactions. The aims of this study were to demonstrate the role of galls mediating multitrophic interactions: (i) investigating which traits influence the survival success of P. oligophaga, considering and describing all the different types of enemies present in the community; (ii) what metabolic changes the different groups of natural enemies promote in the chemical and structural composition of these galls, and finally (iii) how specialized tissues depend on the specific stimuli of the galling in the latter stages of development. Among the analyzed characteristics, parenchyma thickness was negatively related to the probability of occurrence of some galling natural enemies, while the height of the gall on plants was positively related. Despite the structural complexity presented by these galls, P. oligophaga is attacked by a variety of organisms. The activities of the natural enemies studied on galls tissues resulted in metabolic collapse and generalized degradation, similar to natural senescence. Thus, only galling is capable of maintaining the metabolism of the gall, with the allocation and accumulation of specific substances identified in the nutritive tissue (lipids and proteins) and storage (starch). The tissues of the galls are, therefore, totally dependent on the stimulus caused by the galling even in mature stages.