International Union for the Study of Social Insects (IUSSI2018), August 5-10, 2018 in Guarujá, Brazil.

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Labral gland in termites

Author(s):
Valeria Danae Palma Onetto, Valeria Danae Palma Onetto , Barbora Křížková , Thomas Bourguignon , David Sillam-Dussès , Jan Šobotník
Institution(s):
1 University Paris 13 - Sorbonne Paris Cité, Laboratory of Experimental and Comparative Ethology, Villetaneuse, France; 2 Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic; 1 University Paris 13 - Sorbonne Paris Cité, Laboratory of Experimental and Comparative Ethology, Villetaneuse, France; 2 Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic ; Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic ; 1 Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic; 2 Okinawa Institute of Science & Technology Graduate University, Tancha, Onna-son, Okinawa, Japan ; 1 University Paris 13 - Sorbonne Paris Cité, Laboratory of Experimental and Comparative Ethology, Villetaneuse, France Institute of Research for Development – Sorbonne Universités; 2 Institute of Ecology and Environmental Sciences of Paris, Bondy, France ; Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic
Termites possess a complex communication system due by a rich set of exocrine glands. Among them, the labral gland represents one of the most understudied gland of all. Its presence is well established in termite soldiers of all species studies so far. It has been occasionally reported in alate imagoes, but never in workers until now. Here, we report the development of the labral gland in: workers of 27 species and imagoes of 33 species across Neoisoptera representatives, studied using histological procedures, in order to shed light on the evolution and function of this gland in termites. All investigated species possess a labral gland which consists of class 1 secretory cells. In most cases, it is formed by two secretory regions located at the ventral side of the labrum and dorsal hypopharynx. Some common features of the secretory cells in all castes (including soldiers from previous studies) are the abundance of smooth endoplasmic reticulum, which is an organelle known to produce lipidic and often volatile secretions; presence of apical microvilli, allowing secretion release from the secretory cells; and cuticular modifications at the dorsal side of the labrum and ventral hypopharynx, allowing the secretion to be released from the body. The anatomic homology between the labral gland in imagoes, workers and soldiers, make it likely that the gland appeared during the early evolution of termite ancestors, and remained as an organ of primery importance. Based on our observations, we believe that the labral gland is involved in communication rather than in defence as previously suggested. However, the role of the labral gland remains to be confirmed.
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