Chemical Defense in Harvestmen (Arachnida, Opiliones): Do Benzoquinone Secretions Deter Invertebrate and Vertebrate Predators?

Abstract

Abstract-Two alkylated 1,4-benzoquinones were identified from the defensive secretion produced by the neotropical harvestman Goniosoma longipes (Gonyleptidae). They were characterized as 2,3-dimethyl-1,4-benzoquinone and 2-ethyl-3-methyl-1,4-benzoquinone. We tested the effectiveness of these benzoquinone secretions against several predator types, including invertebrates and vertebrates. Different predators were exposed to the harvestmen's gland secretion or to distilled water in laboratory bioassays. Our results indicate that secretions containing the 1,4-benzoquinones released by G. longipes can be an effective defense against predation, and that the effectiveness of the secretion is dependent on the predator type. The scent gland secretion repelled seven ant species, two species of large wandering spiders, and one frog species, but was not an effective defense against an opossum. Our study also demonstrates that the scent gland secretion of G. longipes can work as a chemical shield preventing the approach of three large predatory ants for at least 10 min. The chemical shield may protect the harvestman against successive attacks of the same ant worker and also allow the harvestman to flee before massive ant recruitment. Our data support the suggestion that chemical defenses may increase survival with some but not all potential predators. This variation in defense effectiveness may result from many interacting factors, including the attack strategy, size, learning ability, and physiology of the predators, as well as the chemical nature of the defensive compounds, type of emission, and amount of effluent released by the prey.

Harvestman Phenols and Benzoquinones: Characterisation and Biosynthetic Pathway

“…Gonyleptid scent gland exudates are mainly composed of vinyl ketones and their hetero-Diels-Alder adducts [3][4][5], alkyl phenols [3,[6][7][8][9][10] and benzoquinones [3,6,[11][12][13][14].…”

“…They are known to be toxic and therefore are employed by beetles [17][18][19][20], earwigs [21], termites [22] and harvestmen [12,13] as a defence against natural predators. Additionally, their antimicrobial activity protects cockchafer larvae [23] and adult harvestmen [11] against pathogens, such as bacteria and fungi.…”

“…Additionally, the biosynthetic pathway of the 2-ethyl-1,4-benzoquinone produced by Magnispina neptunus (Gonyleptidae) was investigated using 13 C-labelled precursors.…”

Foraging, oviposition sites and notes on the natural history of the harvestman Heteromitobates discolor (Opiliones, Gonyleptidae)

“…The latter are probably more humid because they are by the river and also probably less visited by predators than the vegetation. Although larger trechaleid spiders are also found on such boulders, harvestmen might be chemically and mechanically protected from their attacks (Machado et al 2005;Souza & Willemart 2011;Dias & Willemart 2013;Segovia et al 2015a, b). It is still not clear why some harvestmen forage on the vegetation and others on the floor.…”

Exploring the global animal biodiversity in the search for new drugs – Spiders, scorpions, horseshoe crabs, sea spiders, centipedes, and millipedes

“…Harvestmen of the genus Goniosoma (Arachnida, Opiliones: Gonyleptidae) secrete volatile alarm substances as well as alkylated 1,4-benzoquinones from exocrine glands on their cephalothorax when confronted with impending danger [43,44]. [57].…”