Genotype and social environment influence female-female interactions in a non-social insect

Factors shaping social interactions between females are understudied in non-social insects. We tested whether female–female investigation, aggression and same-sex sexual behaviour (SSB) are influenced by genotypic and environmental factors in the Hawaiian field cricket, Teleogryllus oceanicus. Males ordinarily sing to attract females, but some are silenced by an X-linked mutation (flatwing) that protects males against an eavesdropping parasitoid fly and impacts female gene expression. To test how the rapid evolution of silence impacts female social behaviour, we matched or mismatched females by genotype and observed them in paired trials exposed to male song or silence. The song treatment mimicked normal cricket populations versus those in which flatwing has fixed. Most female–female interactions involved social investigation characterized by unescalated antennal contact. Aggression and SSB also occurred but were less frequent. Female pairs interacted more in the presence of male song, and this plasticity was augmented when female genotypes matched. This implies that male song is a catalyst for female social interaction, and its evolved loss may reduce investment in female intrasexual interactions in a genotype-dependent manner. We advocate for wider investigation of the function and fitness consequences of female–female behaviour, a phenomenon likely to be neglected in many taxa.