Abstract
Army ants are keystone species in many tropical ecosystems. Yet, little is known about the chemical compounds involved in army ant communication. In the present study, we analyzed the volatile mandibular gland secretions—triggers of ant alarm responses—of six Neotropical army ant species of the genus Eciton (outgroup: Nomamyrmex esenbeckii). Using solid-phase microextraction, we identified 12 chemical compounds, primarily ketones with associated alcohols, one ester and skatole. Most compounds were shared among species, but their relative composition was significantly different. By comparing chemical distances of mandibular gland secretions to species divergence times, we showed that the secretions’ compositions are not strictly determined by phylogeny. By identifying chemical bouquets of seven army ant species, our study provides a valuable comparative resource for future studies aiming to unveil the chemicals’ precise role in army ant alarm communication.
Highlights
Exocrine gland secretions play fundamental roles in interactions of arthropods with each other and with their environment (Eisner, 2003)
Majors are known to emit alarm pheromones from their mandibular glands when disturbed and our study focused on this particular caste (Brown, 1959)
Compared to the study of Keegans et al (1993), our analyses revealed a more complex chemical blend of mandibular gland volatile organic compounds (VOCs) in Eciton ants, which might be attributed to the development of more enhanced chemical analytical techniques
Summary
Exocrine gland secretions play fundamental roles in interactions of arthropods with each other and with their environment (Eisner, 2003). Common are defensive secretions, which often are evolutionarily conserved (Hefetz, 1993; but see Brand, 1978) Besides their role in repelling opponents, defensive secretions in social insects often serve as alert signals to nestmates (e.g., formic acid in formicine ants; Wilson & Regnier, 1971). In contrast to these unspecific alarm-defense compounds, many social insects evolved specific alarm signals aiming to recruit nestmates (“aggressive alarm” sensu Wilson & Regnier, 1971). Natural selection drives such aggressive alarm signals to diversify among sympatric ant species (see Leonhardt et al, 2016; Wilson & Regnier, 1971)
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