Abstract
Labial glands are present in all castes and developmental stages of all termite species. In workers, their secretion contains a food-marking pheromone and digestive enzymes, while soldier secretion plays a defensive role. However, these functions were studied only in a limited set of species, and do not allow drawing general conclusions. Hence, we have investigated the chemical composition of the labial gland extracts from soldiers and workers in 15 termite species belonging to 6 families using an integrative approach based on proteomic and small-molecule profiling. We confirmed the presence of hydroquinone and cellulase in the labial glands of workers, and we identified new toxic compounds in soldiers and workers of several species. Our results highlight the dual role of labial gland secretion, i.e. the defensive role in soldiers and workers of several termite species, and the digestive function in workers.
Highlights
In contrast to Hymenoptera for which about a hundred different exocrine glands are known [1,2], only 17 exocrine glands have been described in termites [3]
Similar defensive purpose has been attributed to the labial glands of workers in some soldierless termites [22]. These functional differences between castes are coupled with cell morphology [5,23,24,25]; in workers, the labial gland acini are always composed of more types of secretory cells than in soldiers, in which the most abundant cell type is structurally similar in all termite taxa [5,24,26,27,28,29]
All samples used for MALDI-TOF and Gas Chromatography - Mass Spectrometry (GC-MS) were stored in the solvent for 24 hours at 4uC, filtered and kept at 220uC until use, while samples for SDS-PAGE were homogenized with a teflon pestle homogenizer and stored at 280uC till use
Summary
In contrast to Hymenoptera for which about a hundred different exocrine glands are known [1,2], only 17 exocrine glands have been described in termites [3]. Labial glands ( called salivary glands) occur in all castes and developmental stages of all termite species [4,5]. Similar defensive purpose has been attributed to the labial glands of workers in some soldierless termites [22] These functional differences between castes are coupled with cell morphology [5,23,24,25]; in workers, the labial gland acini are always composed of more types of secretory cells than in soldiers, in which the most abundant cell type (the only in Macrotermes) is structurally similar in all termite taxa [5,24,26,27,28,29]
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