Feeding Dimorphism in a Mycophagous Nematode, Bursaphelenchus sinensis

Phenotypic plasticity has been widely reported in animals and can drive investment in new biological characters that engender ecological adaptability. The nematode family Diplogastridae, especially Pristionchus pacificus with its dramatic stomatal (feeding) dimorphism, has become an important model system to analyze the evolutionary and developmental aspects of polyphenism. However, this plasticity has not been confirmed in other nematode groups. In the present study, we experimentally examined the feeding dimorphism of a fungal feeding free-living nematode, Bursaphelenchus sinensis. In a laboratory culturing experiment, the nematode expressed dimorphism, i.e., a small proportion of the population manifested as a predatory form. This form only occurred in females and was not clearly influenced by the presence of potential prey species. In addition, the ratio of the predatory form to the mycophagous form varied among different fungal food species grown in monoculture on different culture media. The predatory form of B. sinensis was typologically similar to the monomorphic (specialized) predators belonging to the same family. However, some essential morphological characters were slightly different from the specialized predators, and their behaviours were clearly disparate, suggesting that predation in B. sinensis is derived from a different phylogenetic origin than that of the specialized predators.