Morphology and closing mechanism of the mandibular gland orifice in ants (Hymenoptera: Formicidae)

Abstract

The mandibular gland of ants releases chemical compounds with functions ranging from nestmate alarm and recognition to antimicrobial defense. While the morphology of this ethologically important gland is well investigated in several species, the mechanism of secretion release in ants was not explicitly addressed so far. To clarify this question, we examined the anatomy of the gland orifice in ant species from 14 different subfamilies employing different techniques. The orifice close to the mandibular base is located on an area called mandalus. Our investigations revealed variation in mandalar shape, with clear trends in different subfamilies. By contrast, the internal organization is remarkably congruent across all investigated species. The thin external mandalar cuticle is always connected to the mandibular gland duct by a cuticular lamella, visible as a characteristic anchor-shaped structure in cross section. The slit-like gland orifice at the distal end of the mandalus is usually crescent-shaped. In some ant species with specialized mandibles such as trap-jaws, the organization of the orifice area is adapted to the mandibular shape, but always retains the general internal organization. No muscles were found in association with the orifice, nor with any other part of the mandibular gland. However, the base of the mandalus is connected to the prepharyngeal sucking pump by a cuticular ligament. Additionally, it is continuous with the conjunctiva connecting the mandible to the head capsule. We propose that retraction of the sucking pump by the muscle M. tentoriobuccalis, potentially in concert with opening of the mandible, stretches out the ligament and thus pulls on the mandalus and mandalar lamella to open the gland orifice and allow for secretion release. This hypothesis is congruent with findings on other aculeate Hymenoptera and expands our knowledge on the function of an important gland of ants.

Survey of the exocrine glands in workers of the ant Leptanilla clypeata

“…The long lamella occupies a considerable part of the mandible lumen (Fig. 2c), which is typical for Leptanillinae (Richter et al 2021a). The secretory part of the gland is made up by a large reservoir in which 13 gland cells open at each side (Fig.…”

The feeding apparatus of ants: an overview of structure and function

“…To visualize the ant feeding system, we created 3D renders based on micro-computed tomography (µCT) scans of Leptomyrmex unicolor Emery, 1895 (Formicidae, Dolichoderinae) and Formica rufa Linnaeus, 1761 (Formicidae, Formicinae), both used in previous work [ 21 , 45 ] and published on Zenodo. Both species are omnivores, with a significant amount of arthropod prey but also nectar and in the case of Formica aphid exudates as part of their diet.…”

Anti-Adhesive Surfaces Inspired by Bee Mandible Surfaces

“…There is vast literature on Hymenoptera-mandibles [12][13][14]. However, a detailed anatomical investigation of honeybee mandibles, which frequently come into contact with sticky propolis and plant resins, was only recently conducted [15].…”