Sex-specific viral susceptibility of Caenorhabditis elegans nematodes

The sex of an organism affects a variety of phenotypes including pathogen susceptibility. Hermaphrodites of the androdioecious model organism Caenorhabditis elegans can be infected by an intestinal virus: the Orsay virus. The viral susceptibility of C. elegans males has not been studied, but it is known that males are more resistant to a pathogenic fungus than hermaphrodites. We investigated the viral susceptibility of C. elegans males and found that male populations are less often successfully infected by the Orsay virus than hermaphrodite populations. Infection in hermaphrodites causes upregulation of genes of the Intracellular Pathogen Response (IPR) which counteracts infection. We have found that several genes in this pathway are constitutively higher expressed in males and that their expression increases even further after infection. Additionally, we infected a strain with a natural mutation in the RNA interference pathway which makes the hermaphrodites highly susceptible. We found that males of this strain are as susceptible as the hermaphrodites. Deep-sequencing of small RNAs from infected populations supports that RNAi processing of the virus differs between the sexes. Therefore, both the RNAi and IPR pathway may determine sex-specific susceptibility. In nature C. elegans males are rarely found among populations, but male frequencies can increase upon experiencing unfavourable conditions which facilitates adaptation in the lab. Preliminary data suggests that males are less attracted to the lysate of infected hermaphrodites than that of uninfected hermaphrodites. The presence of relatively resistant males with a preference for healthy hermaphrodites within a population could facilitate longer-term survival of the species. This may be one of the answers to why males occur in a species that could also exist without them.