Comparative morphology and chemical profile of the metapleural gland in two ants: Paraponera clavata and Pachycondyla crassinoda.

Ants possess a pair of metapleural glands whose secretions are associated with antimicrobial defense and colony hygiene. Despite their importance, comparative studies integrating morphology and chemical characterization of these glands remain limited, particularly among poneromorph ants. This study investigated the hypothesis that species belonging to different ant lineages exhibit differences in the morphology and chemical composition of the metapleural glands. These features were evaluated in workers of Paraponera clavata (Fabricius, 1775) (Paraponerinae) and Pachycondyla crassinoda (Latreille, 1802) (Ponerinae), two phylogenetically distant species with distinct ecological habits. Histological and morphometric analyses were conducted to describe gland structure, including secretory cells, reservoir, and sieve plates, and gland extracts were analyzed by gas chromatography-mass spectrometry (GC-MS) to identify chemical compounds. The metapleural glands of both species share the same general organization but differ in ostiole morphology, the number of sieve plates, and reservoir size, with the latter being larger in P. clavata. GC-MS analyses revealed both shared and species-specific compounds, with P. clavata exhibiting a greater chemical diversity, including the long-chain alcohols 1-octacosanol and 1,30-triacontanediol. Notably, 1-octacosanol has rarely been reported in ants, whereas 1,30-triacontanediol appears to have not been previously documented in the family Formicidae. These results demonstrate that the metapleural gland shows some morphological and chemical variation between phylogenetically distant species and provide new data that contribute to the understanding of the diversity and evolution of exocrine glands in Formicidae.