New reports on the association between eggs and sclerotium-forming fungi in Neotropical termites with insights into this mutualistic interaction

Abstract

Over many years of co-evolution, termites and fungi have developed varied interactions. Sclerotia, termed termite balls, are fungal resting structures often mixed with termite eggs, with many reports in temperate areas. Here, we show that this interaction is more widespread than suggested, by reporting the occurrence of fungal sclerotia harboured in the nests of four Neotropical termitids: Cornitermes cumulans, Silvestritermes euamignathus (Syntermitinae), Velocitermes heteropterus, and Nasutitermes corniger (Nasutitermitinae). We performed termite–fungus recognition bioassays and carried out morphometrical, histological, and histochemical analyses on the sclerotia, assuming that they vary in their stored materials according to the maturation stage. Morphometrical and morphological features varied among the sclerotia associated with the different termite species. Moreover, workers preferentially carried related sclerotia, suggesting a species-specific interaction, and did not mistake them for eggs. Immature and mature sclerotia varied in the concentration of stored proteins, polysaccharides, and melanin. This facultative mutualism is advantageous for the sclerotia because they are kept in a competitor-free environment and, in turn, are likely to serve as an additional source of termite digestive enzymes. We provide new findings concerning the geographical distribution, termite species, and nesting habits related to this termite–fungus association, reinforcing its parallel evolution.