Comparative study of forewing surface ultrastructure in Eneopterinae crickets, with possible implication on male song...

Acoustic signals play a key role in animal communication and are shaped by both sexual and natural selection. In crickets, males produce sound using specialized forewing structures, leading to a strong sexual dimorphism in forewing morphology and functioning. While the macroscopic structures of the forewings and sound-production mechanism are well understood, they have been little studied at the microscopic scale. Yet surface ultrastructure of the forewings' membrane likely plays a role in shaping its physical properties and vibratory behavior. In the subfamily Eneopterinae, species belonging to the tribe Lebinthini show remarkable high-frequency calling songs that could be partly explained by differences in terms of surface ultrastructure. In the present study, we used scanning electron microscopy to compare male and female forewing membrane ultrastructure of 33 species of Eneopterinae crickets, including species producing low-frequency and high-frequency calling songs. We highlighted a great diversity of ultrastructure within the subfamily. Our results show remarkable differences between males and females of the non-lebinthini species concerning the hexagonal cells on the dorsal face of the forewings, and between the males of the different tribes. The presence of pronounced hexagonal cells in Lebinthini males (high-frequency singers), in contrast to the flattened harp membrane of non-Lebinthini species (low-frequency singers), added to the strong sexual dimorphism of the structures, suggests a link between the presence of these hexagonal structures and the sound-production mechanisms.