Differential phoretic host use among sympatric Caenorhabditis nematodes and an association with invasive nitidulid beetles in southwestern Germany

Little is known about the natural history of most Caenorhabditis nematodes, despite their importance as a model system in biology. While these nematodes rely on invertebrate hosts to disperse to new habitats, host use for most species has not been characterized. We surveyed the invertebrate community of a habitat containing three sympatric Caenorhabditis in southwestern Germany, determining differential and specific host use for each of these co-occurring species. We documented a specific association between C. sp. 8 and two species of invasive nitidulid beetles, and a particularly strong association of the nematode with the beetle Stelidota geminata , where we recovered more nematodes per individual beetle and a higher proportion of beetles carrying nematodes for S. geminata than for the co-occurring Epuraea ocularis . Our results provide evidence for group dispersal using beetles in C. sp. 8, supporting previous observations of collective dispersal behavior in this species, and establish a starting point for further dissecting the evolutionary and mechanistic causes and consequences of interactions between Caenorhabditis nematodes and their host species in ecologically relevant conditions.