A preadaptation for fungal gardening in Coptotermes formosanus Shiraki as a result of tunnel excavation

When encountering wood, Coptotermes formosanus workers do not simply “eat” their way through. Instead, they tunnel through wood according to the same mechanics described for soil excavation. The process involves a queue of excavators that remove parcels of soil or wood from the burgeoning ends of tunnels, and then deposit these along tunnel walls. The result is that tunnels within wood and in soil near wood sources become lined, and lengths of unused tunnels become packed, with excavated wood fragments and subsequently coated with a fecal carton envelope. This fecal envelope consists of a mixture of feces, saliva, soil, wood particles, and cuticular remnants of dead nest mates, and may be considered an extended refuse pile. The evolution of the termite/fungus symbiosis in the subfamily Macrotermitinae (Termitidae) is unclear, but it has been suggested that the evolution of the fungal garden system seen in the Macrotermitinae today originated in a Coptotermes-like ancestor when the carton of central mound nests was opportunistically invaded by soil fungi.  Areas of tunnel where wood fragments are placed in contact with soil then covered in feces present an invasion route that may be more likely in light of the known fungistatic properties of termite fecal carton.  The manner in which the simple mechanics of tunnel excavation create this novel microbial microniche, the consumption of the sequestered wood and carton, and the fungus and nematodes that inhabit it will be discussed.