From wood- to humus-feeding: an important trend in termite evolution
1992
Noirot, C. (Bourgogne Univ., Dijon (France). Lab. de Zoologie)
The evolution of the Isoptera was strongly constrained by their food and by the symbiotic microorganisms which enable termites to digest lignocellulosic components of the plant biomass. This paper reviews the utilization of the last stage in the degradation of this biomass, the humus. This dietary specialization is observed in more than half the termite genera, but appeared only in the "higher termites" (family Termitidae) with a highly polypeptic pattern. Although the physiology of the humus-feeding termites is hardly known, it involves the utilization (via bacterial fermentations) of aromatic, lignin-derived compounds, in contrast to the predominant use of cellulose in xylophagous or harvesting species. The concomitant modifications of the gut disclose a great diversity, but these are marked by an increase in length, in volume and in compartmentation of the hindgut. Various differentiations of the proctodeal cuticle are frequently (but not always) also present, some of them ("cuticular filaments") being attachment sites for bacteria. In all termite species, the hindgut, with its symbiotic micro-organisms, realizes a complex micro-ecosystem inside the insect. A co-evolution of the termites with their intestinal ecosystem is proposed, with a major breakthrough having occurred when the flagellated Protista, which are dominant in the lower termites, were lost during the differentiation of the higher termites. This allowed the diversifications of the gut and the diet, ending in the humus-feeding adaptation.
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