Distribution and phylogenetic analysis of termite egg-mimicking fungi 'termite balls' in Reticulitermes termites

摘要

To understand the evolution of parasitism, a fundamental question is what influences the distribution of globally distributed parasites among different hosts. Reticulitermes termites often harbor brown fungal balls, called "termite balls," alongside their eggs. The termite ball was identified as the selerotium of a parasitic corticioid fungus, an undescribed species of genus Fibularhizoctonia, which mimics termite eggs physically and chemically so as to be protected in termite nests. This phenomenon has been found for Reticulitermes species in Japan and the United States, but not all the Reticulitermes species in these countries have termite balls. To identify factors influencing the distribution of termite balls among their host species, we conducted wide-range sampling in the temperate zone and in subtropical zones in Japan and Taiwan. We also conducted phylogenetic analyses of termite ball fungi and their host termites based on molecular data. In Amami-Oshima Island, R. amamianus Morimoto colonies bad termite balls only in temperate highland regions, but no termite balls were found in its subtropical lowland region. The introduced termite R. kanmonensis Takematsu had termite balls as well as sympatrically occurring R. speratus (Kolbe). The termite ball fungi isolated from these two species showed no significant molecular difference, suggesting no host race formation. Phylogenetic analysis showed that R. kanmonensis in Japan did riot diverge from R. flaviceps (Oshima), which has no termite balls, in Taiwan. Analyses of termite ball distribution among nine Reticulitermes species suggested that climate is the most important factor restricting the distribution of the termite ball fungi.