Symbionts in Hodgkinia-free cicadas and their implications for co-evolution between endosymbionts and host insects.

Symbiotic systems of sap-feeding auchenorrhynchan insects of the order Hemiptera provide a unique perspective for uncovering complicated insect-microbe symbiosis. Previous evidence suggested that cicadas lacking the symbiont Hodgkinia harbor Sulcia in the bacteriomes and the yeast-like fungal symbiont (YLS) in the fat bodies; however, YLSs were also detected from the bacteriome sheath in three cicada species which separately belong to two phylogenetically closely related tribes, Sonatini and Polyneurini. We comprehensively investigated the symbionts associated with bacteriomes and fat bodies in Sonatini and Polyneurini and analyzed the co-phylogeny between 65 cicada species and related symbionts (Sulcia and YLSs). We revealed that YLSs can commonly colonize the bacteriome sheath besides the fat bodies in these two tribes. Although the phylogeny of YLSs associated with Sonatini, Polyneurini, and some other taxa is locally concordant with that of host cicadas, relationships of YLSs harbored in different host lineages are generally incongruent with that of Cicadidae. More independent replacement events in the loss of Hodgkinia/acquisition of YLS were revealed in Cicadidae, reinforcing the hypothesis that the pathogenic ancestor of YLSs independently infected different lineages of host cicadas. The phylogeny of the very conservative Sulcia generally mirrors the host phylogeny, but Sulcia associated with some taxa (e.g., Sonatini, Platypleurini) of Cicadidae are incongruent with their hosts. This indicates that genetic variation of Sulcia occurred in these cicada lineages. Results of this study contribute to a better understanding of symbiont colonization in the symbiotic system of auchenorrhynchan insects and co-evolutionary relationships between Auchenorrhyncha and related symbionts. IMPORTANCE Obligate symbionts in sap-sucking hemipterans are harbored in either the same or different organs, which provide a unique perspective for uncovering complicated insect-microbe symbiosis. Here, we investigated the distribution of symbionts in adults of 10 Hodgkinia-free cicada species of 2 tribes (Sonatini and Polyneurini) and the co-phylogeny between 65 cicada species and related symbionts (Sulcia and YLSs). We revealed that YLSs commonly colonize the bacteriome sheath besides the fat bodies in these two tribes, which is different with that in most other Hodgkinia-free cicadas. Co-phylogeny analyses between cicadas and symbionts suggest that genetic variation of Sulcia occurred in Sonatini and some other cicada lineages and more independent replacement events in the loss of Hodgkinia/acquisition of YLS in Cicadidae. Our results provide new information on the complex relationships between auchenorrhynchans and related symbionts. [ABSTRACT FROM AUTHOR]