Comparative morphology of the labial gland in Formicidae

The labial gland is an important exocrine gland in ants and is thought to contribute to food processing and trophallaxis. In this study, the morphology of the labial gland was examined in 12 species from 4 subfamilies-Ponerinae, Formicinae, Dolichoderinae, and Myrmicinae-using light and electron microscopy (SEM, TEM). Our results reveal that gland morphology is more similar among closely related species, suggesting a stronger correlation with phylogeny than with diet. The morphology also appears to relate to social behavior, particularly trophallaxis. Formicine species, which rely heavily on trophallaxis, possessed the largest relative reservoir size, whereas the two examined myrmicine species, which have reservoirs absent, are known to rely little or not at all on this behavior. Ultrastructural observations showed abundant rough endoplasmic reticulum in all species, indicating protein-rich secretions in the labial gland. Ponerine species displayed the acinar type, characterized by short microvilli in the apical cell region and a ramified canaliculi system that delivers secretion to the duct. Species from other subfamilies exhibited the tubular type, with long apical microvilli that increase the apical surface and appear to facilitate secretion discharge. This study provides new comparative data on labial gland morphology and reveals potential phylogenetic, behavioral, and ecological variation that will require further study to confirm and fully understand.