Upregulation of juvenile hormone signaling-related gene expression in non-reproductive individuals of the queenless ant Pristomyrmex punctatus

In major eusocial species of Hymenoptera, regulatory mechanisms of queen/worker differentiation have been studied a lot. From the results, it was proved that juvenile hormones (JHs) act as one of a key endocrine factor for reproductive division of labor. However, most past studies dealt with species with clearly differentiated and fixed castes between reproductive and non-reproductive individuals. In such cases, although we want to explore factors regulating reproduction, these may be masked by a lot of molecular differences derived from various caste specific phenotypes. In order to solve this problem, in this study, we focused on the queenless ant Pristomyrmex punctatus, which showed reproductive division of labor between morphologically and genetically uniform workers. To elucidate molecular mechanisms of reproduction in P. punctatus, we first isolated a vitellogenin gene (PripuVTG1) and established it as a molecular marker for egg production which is necessary for convenient determination of reproductive states and discrimination between reproductive and non-reproductive individuals. Subsequently, we analyzed gene expression correlations between this reproductive marker gene and candidate regulatory genes consisting of major components of JH and insulin/insulin-like growth factor signaling (IIS) signaling, which regulate reproduction upstream of JH signaling. As a result, Expressions of JH signaling-related genes correlated negatively to PripuVTG1 expression, suggesting the negative regulatory relationship between JH signaling and reproduction. Our findings are expected to be useful for understanding how various styles of sociality have evolved in insects.