Wolbachia as a potential driver of chemical character displacement in Crematogaster ants

The endosymbiont Wolbachia infects at least 70% of examined arthropod species, causing a range of effects including cytoplasmic incompatibility (CI). Through CI, the high costs of hybridization may cause divergent selection on the recognition traits of carriers of incompatible strains. However, we still have very limited knowledge of Wolbachia’s effects in most of its hosts, particularly amongst social insects. The Neotropical ant Crematogaster levior is found across Amazonia. In French Guiana, two divergent cuticular hydrocarbon chemotypes are found in complete sympatry, with no morphological, ecological, or behavioral differences. However, in Peru there is only a single chemotype that appears to contain both of the compounds found uniquely on each of the FG chemotypes. Queens of both divergent chemotypes also have a similar ‘hybrid’ chemotype, and are indistinguishable. However, males appear to have a chemotype more closely resembling the worker type within their nest. Of more than 50 examined nests, 100% of the workers harbor Wolbachia. Using multi-locus strain typing, we have found  a single Wolbachia strain in the Peruvian populations, but two divergent Wolbachia strains in French Guiana. Each strain belongs to a different supergroup. Each chemotype carries a different Wolbachia strain. The divergence in Wolbachia strains and chemotypes correlates with genetic differences in the ants. We propose that selection for reproductive isolation between Wolbachia strains may have caused chemical character displacement in C. levior in French Guiana. Given the caste-specific chemistry this effect may be mediated by male-worker interactions and not queen-male interactions. These findings highlight the potential and underexplored role of Wolbachia in ant speciation and chemical evolution.