LB 25-263 - Going viral: Infections by viruses may affect partner quality in an ant-plant mutualism

Background/Question/Methods:

Some of the most well-studied mutualisms are ant-plant interactions, where partners provide nutrition, protection, or dispersal services to their mutual benefit. Although the ecology and evolution of these interactions has been well studied, how mutualistic traits are molecularly regulated remains largely overlooked. Here, we focused on investigating the molecular basis of bodyguard behavior in the ant species Allomerus octoarticulatus, which aggressively defends its host myrmecophyte, Cordia nodosa, against herbivores. We performed a de novo transcriptome assembly using RNA sequences from 14 ant colonies collected from the Peruvian Amazon. A total of 93,122 transcripts and 67,613 unigenes were generated and functionally annotated using BLAST with the UniProtKB dataset. We obtained 134 Gene Ontology (GO) functional sub-groups in the three main GO categories: ‘biological process (86)’, ‘cell component (17)’ and ‘molecular function (31)’.

Results/Conclusions:

We then analyzed genes that are differentially expressed between high- and low-quality bodyguards and between bodyguards and brood-care workers. We identified 11 genes that were differentially expressed in bodyguards with high and low activity levels. Most of those genes were upregulated (9/11) in ‘good’ bodyguards, including a putative Picorna-like virus. The remaining 2 genes upregulated in ‘bad’ bodyguards corresponded putatively to a Narnavirus and a Dicistrovirus. Potentially, these viruses affect the aggressiveness of ant workers since their expression levels vary with the quality of the mutualist partner. We then performed phylogenetic analysis for the Dicistrovirus we identified using its sequence and sequences of its close relatives previously described infecting Hymenoptera. In the behavioral task comparison, we found 59 differentially expressed genes, most of which were upregulated in brood care workers (58/59) and none of them corresponded to viral expression. Our results provide insights into the molecular bases of ant-plant mutualisms which involve putative viral expression affecting mutualist partner quality. For the first time, our study identified infections by single-stranded RNA viruses in the ant A. octoarticulatus.