Detritivory, coprophagy, and the evolution of digestive mutualisms in Dietyoptera

We review literature on extant detritivores, including cockroaches and term ites, and conclude that coprophagy was the key behavior leading to the evol ution of hindgut fermentation systems in the stem group of Dictyoptera. Cop rophagy exploits concentrated microbial consortia on cellulose based substr ates. These microbes are potential mutualists and food, but they also initi ate degradation of cellulose, detoxify allelochemicals and soften the subst rate, a phenomenon known as the "external rumen". We suggest that the evolu tion of a sophisticated hindgut fauna is a process of internalizing this se lf-assembled microbial community, accompanied by changes in host-microbe in terdependence, the source of microbial inoculum for neonates, and host soci al behavior. Proctodeal trophallaxis evolved from pre-existing intraspecifi c coprophagous behavior when termite ancestors became subsocial, because th e physiology of encystment in oxymonad and hypermastigid flagellates preclu des their transfer via cysts in adult feces. The behavior was reinforced by the benefits of using the trophic stages of flagellates as food. The assoc iation of these flagellates with the dictyopteran lineage is an ancient one , and may have originated as part of the external rumen in the Carboniferou s coal swamps.