Host‐specificity of environmentally transmitted <i>Mycoplasma</i> ‐like isopod symbionts

Summary Mycoplasms are known as pathogens of economic and medical interest in plants, animals and man. Here, we show a positive correlation between the presence of Mycoplasma ‐like symbionts in their isopod hosts and survivorship on low‐quality food. Most isopods that survived feeding on a cellulose‐based low‐quality diet for 90 days harboured ‘ Candidatus Hepatoplasma’ in their midgut glands, while those that died within 90 days mostly either harboured no or other bacterial symbionts. We detected ‘ Candidatus Hepatoplasma’ in all but one of the examined species of terrestrial isopods from different habitats and locations, suggesting an evolutionarily ancient association between terrestrial isopods and their Mycoplasma ‐like symbionts. Phylogenetic analyses clustered symbionts from different populations of the same isopod species together, and clearly distinguished between symbionts of different isopod species, indicating host‐specificity of ‘ Candidatus