Benzoquinones from scent glands of phalangiid harvestmen (Arachnida, Opiliones, Eupnoi): a lesson from Rilaena triangularis

Abstract

In case of disturbance, the phalangiine harvestman Rilaena triangularis (Eupnoi, Phalangiidae) emits a directed jet from large prosomal scent (“defensive”) glands. The pungent-smelling secretion was analyzed by gas chromatography–mass spectrometry and found to contain mainly 1,4-benzoquinone along with 1,4-naphthoquinone and caprylic (=octanoic) acid. While various alkylated benzoquinones are characteristic for the scent gland secretions of many grassatorean Laniatores, this is the first incidence of benzoquinone-based chemical defense in palpatorean harvestmen.

A Model for Phylogenetic Chemosystematics: Evolutionary History of Quinones in the Scent Gland Secretions of Harvestmen

“…Among a multitude of components found in the extracts of eupnoans and dyspnoans herein analyzed (will be published elsewhere), nine quinonic compounds were detected, namely 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), 1,4-naphthalendiol (ND), 6-methyl-1,4-naphthoquinone (MNQ), 2-methoxy-1,4-naphthoquinone (MOQ), 2-methoxy-6-methyl-1,4-naphthoquinone (MMOQ), 4-chloro-1,2-naphthoquinone (CNQ), 2-methyl-9,10-anthraquinone (MAQ), and 2,3-dimethyl-9,10-anthraquinone (DMAQ) (Figure 1). All compounds were already known to us from previous studies (e.g., Raspotnig et al, 2005, 2010, 2015b) and were readily identified by comparison of GC-MS data to authentic reference compounds (analytical data in Table 1). For MMOQ, no authentic reference was available and the position of substituents (methoxy-group in position 2; methyl-group in position 6) is tentatively proposed in analogy to the substitution pattern of the remaining naphthoquinones (e.g., MNQ, MOQ).…”

“…Secretion-loaded filter paper pieces were transferred into 50 µl of hexane and extracted for 30 min. This method of direct sampling of secretion was suitable for many Eupnoi, was applied to confirm the scent gland origin of certain compounds and has already been described in a previous paper in detail (Raspotnig et al, 2015b). The method could not be applied for Dyspnoi (that are reluctant to emit secretion).…”

“…From previous studies we know that the composition of secretions clearly characterizes different opilionid lineages. For instance, and very roughly, alkaloids and terpenes appear characteristic for travunioid Insidiatores, phenolics for lower Grassatores, and a number of acyclic compounds (mainly ketones) as well as quinones have been reported from Cyphophthalmi, Eupnoi, Dyspnoi, and Laniatores (e.g., Eisner et al, 1977; Roach et al, 1980; Duffield et al, 1981; Ekpa et al, 1984; Raspotnig et al, 2011, 2014, 2015a,b; Raspotnig, 2012; Wouters et al, 2013).…”

“…While the distribution of quinones in these two groups is fairly well documented and conclusive (Raspotnig, 2012; Raspotnig et al, 2015a), quinone-production and distribution is almost unknown for suborders Eupnoi and Dyspnoi. Generally, chemical data for the secretions of only a handful of eupnoan and dyspnoan species is available (Wiemer et al, 1978; Ekpa et al, 1985; Raspotnig et al, 2014, 2015b), and these do not indicate ubiquitous, but sporadic quinone-occurrence in a distinct taxonomic pattern. However, this pattern in Eu- and Dyspnoi appears to be highly convoluted with quinone-occurrence being restricted to particular subgroups.…”

Methyl-ketones in the scent glands of Opiliones: a chemical trait of cyphophthalmi retrieved in the dyspnoan Nemastoma triste

“…Regarding scent gland secretions, the chemical composition of exudates appears to reflect the phyletic lineages among opilionids. In detail, suborders are characterized by the presence of (1) naphthoquinones and methyl-ketones in the Cyphophthalmi (Raspotnig et al 2005 , 2012 ; Jones et al 2009 ); (2) naphthoquinones, anthraquinones, and certain acyclic ketones in the Dyspnoi (Raspotnig et al 2010 , 2014 ); (3) naphthoquinones and ethyl-ketones in the Eupnoi (Blum and Edgar 1971 ; Meinwald et al 1971 ; Jones et al 1976 , 1977 ; Wiemer et al 1978 ; Ekpa et al 1985 ; Raspotnig et al 2015 ), and (4) phenols, benzoquinones, terpenes, vinyl-ketones and nitrogen-containing compounds in the Laniatores (e.g., Eisner et al 1971 ; Segovia et al 2015 ; summarized in Raspotnig 2012 ).…”