Living Environment and Basic Features of the Nematodes Associated with Dung Beetle Onthophagus atripennis

Viviparity is a very rare reproductive mode in nematodes, having been documented in only six species. Five of these species have been isolated among the dung beetles Onthophagus, suggesting that studying the environments associated with dung beetles may help shed light on why viviparity evolved in these particular species. Onthophagus atripennis is often closely associated with the viviparous nematode Tokorhabditis atripennis, as well as some other oviparous nematodes. Hence, the system involving T. atripennis and dung beetles could provide valuable insights into the adaptive significance of viviparity in nematodes. To explore this idea, it is essential to first gain a better understanding of the natural habitats of T. atripennis, which remain poorly understood. Therefore, we investigated the nematode communities associated with O. atripennis and identified potential habitats for T. atripennis in environments used by dung beetles. Nematodes associated with O. atripennis and those inhabiting its rearing cases were isolated from samples. Two Tokorhabditis species were isolated from the rearing cases of O. atripennis, suggesting that they inhabit environments used by O. atripennis. Regarding other oviparous nematodes, some appeared to have relatively strong associations with dung beetles, but more detailed studies are needed to confirm their specific habitats. Although further investigations are necessary, the fact that nematodes, including viviparous species, were isolated from environments used by dung beetles provides important information about the potential competitors or predators of T. atripennis in such environments.