Interação cupim – líquen em ecossistema semiárido do nordeste brasileiro

Abstract

Wood is the main dietary item of most termites, but supplementation through assimilation of some nutrients may occur from ingestion of other food resources available in the ecosystem, such as lichens. This study evaluated the effect of the nutritional and chemical composition of lichens on the consumption by C. cyphergaster, besides verifying the dispersal potential of lichen symbionts by these termites. Studies were carried out at RPPN Fazenda Almas, PB, where the foraging of fifteen colonies was monitored for fifteen days by identifying the lichens consumed. Food preference testing and consumption estimates were conducted in the laboratory. The content of N, C, P and secondary compounds were measured. Termites kept in bioassays under a diet exclusive of lichens were dissected for analysis of their food content, and the presence of viable lichen structures for dispersion was verified through staining tests. Fourteen species of lichens were recorded on the C. cyphergaster diet. The mean total lichen consumption was 0.032 mg lichen/g termite (fresh weight)/day, accounting for 105.12g of lichen/ha/yr. The consumption of lichens was significantly affected by the N content and by the C: N and C: P ratios, with N being the element that best explained the consumption by the termites. The distribution of the secondary compounds of the lichens differs significantly between the regions that make up the lichen thallus (thallus blade, apothecium margin and apothecium disc), affecting their consumption by termites. The thallus blade presented the highest content of compounds, followed by the apothecium margin, which are the most consumed regions by the termites, respectively. There was no consumption of apothecium discs. The consumption of lichen layers (upper cortex, algae layer and medulla) by termites was also selective. The most consumed layers in the stems were the upper cortex and the algae layer, with rejection of the medullary layer. In the alimentary canal of the termites, broken spores and algae with potential vitality for relichenization were found. Progressive growth in algal mortality along the termite alimentary canal (foregut, gut and rectum) was observed. The photobiont morphology was also different between cells extracted from in natura thallus and algae present in the feces of termites. Results indicate the balance between nutrients and secondary metabolites play a fundamental role in food preferences and consumption rates by C. cyphergaster. The hardness and roughness of lichen tahllus structures can also modulate consumption strategies. The vitality of photobionts dispersed by termites was confirmed, demonstrating the dispersal potential of lichens via feces of these insects.