Meeting Abstract
In the rove beetle subfamily Aleocharinae (Coleoptera: Staphylinidae) symbiosis with ants (myrmecophily) has evolved independently dozens of times. The predisposition to evolve myrmecophily has been attributed to an abdominal defensive gland in free-living species that equips the beetles for entry and exploitation of ant colonies. In some symbiotic species, the gland has undergone further specialization to synthesize and secrete compounds that manipulate ant behavior. The tergal gland is therefore a substrate for selection that has likely facilitated the repeated emergence of myrmecophily in Aleocharinae. Despite being a pivotal structure for this remarkable convergence towards myrmecophily, the molecular architecture of the gland and its chemical evolvability are poorly understood. We exploited a free-living aleocharine, Dalotia coriaria, to ask how this evolutionary novelty arises developmentally. The gland consists of two exocrine cell types: epithelial secretory cells (termed D2) that form a reservoir into which fatty acid derivatives are secreted, and classical glandular units (termed D1), composed of a biosynthetic bulb and duct cell, which synthesize irritant benzoquinones. The benzoquinones are trafficked into the D2 reservoir where they dissolve, creating a defensive secretion. Using RNAi, we find that development of both D1 and D2 cell types requires the cooperative activity of the posterior Hox proteins abdominal A and Abdominal B. Strikingly, we find that the thoracic Hox protein Ultrabithorax is also involved: Ubx knockdown causes loss of benzoquinone-producing D1 cells. Hence, evolution of an unusual Hox code in aleocharines underlies the capacity of these beetles to manufacture defensive chemicals, and consequently, their convergent infiltration of ant colonies.
