Ultramorphology, diversity and quantitative analysis of antennal sensilla in Diacamma ants (Formicidae: Hymenoptera: Ponerinae)

Abstract

Abstract Background Antennal sensilla are vital sensory organs that facilitate communication, navigation, and environmental adaptation in ants. Variations in sensillar organization are often associated with ecological and behavioral differences among species. The queenless ponerine genus Diacamma provides an important model for examining sensory adaptation because its species occupy distinct microhabitats while maintaining complex social communication through gamergate-based reproductive systems. The present study compares the antennal sensilla of Diacamma scalpratum and Diacamma rugosum jerdoni using scanning electron microscopy (SEM). Results Both species share common sensillar types, Böhm bristles, sensilla chaetica (long, distal, and stout forms), sensilla trichodea, sensilla basiconica, sensilla trichodea curvata, sensilla coeloconica, and sensilla ampullacea, yet differ in their density and subtype diversity. Diacamma scalpratum has a higher percentage of sensilla chaetica on the apical antennal segment (71.23% of the total sensillar count versus 64.90% in D. rugosum jerdoni ), with the long and stout forms, together with sensilla coeloconica I and sensilla trichodea curvata II, characteristic of this species. In contrast, D. rugosum jerdoni possesses a greater number of sensillar subtypes (Shannon H′ = 1.69 versus 1.42), including additional sensilla basiconica and trichodea subtypes. Quantitative analysis of the apical antennal segment revealed significant interspecific variation in sensillar composition (χ 2 = 17.86, df = 8, p < 0.05). Peg morphometry further demonstrated an inverse relationship between peg length and width across sensillar subtypes. Conclusions The comparative differences observed between the two Diacamma species suggest that antennal sensillar organization may vary in association with habitat structure, foraging ecology, and species-specific sensory demands. Although functional interpretations are inferred from external morphology and require physiological validation, the present study expands current knowledge of ponerine antennal ultrastructure and provides a comparative framework for future investigations of sensory evolution and ecological adaptation in ants.