Chemical and evolutionary analysis of the scent gland secretions of two species of Gonyleptes Kirby, 1819 (Arachnida: Opiliones: Laniatores)

Abstract

The subfamily Gonyleptinae is the second largest in Gonyleptidae, harboring over 100 species. Gonyleptinae is polyphyletic, nestled in the clade K92, and despite its richness, several species of that subfamily have not had their chemicals of the defensive secretions analyzed. Among these are Gonyleptes curticornis (Mello-Leitão, 1940) and G. horridus Kirby, 1819, the latter being particularly important, because it is the type species of the genus, which in turn names the subfamily Gonyleptinae. Gonyleptes horridus is also used in many phylogenetic analyses, be it using morphological or molecular data. The chemical study of the secretions of these two species by GC–MS and ¹H NMR showed the presence of 1-(6-isopropyl-3,4-dihydro-2H-pyran-2-yl)-methylbutanone, 1-(6-isopropyl-3,4-dihydro-2H-pyran-2-yl) isobutanone and 4-methyl-1-hepten-3-one in both species. On the other hand, 4-methyl-1-hexen-3-one was observed only in G. curticornis, and 7-methyl-2-octanol is exclusive of G. horridus. All vinyl-ketones identified have already been described for Gonyleptidae. We ran an Ancestral Character State Reconstruction (ASR) analysis under three different conditions to infer the evolution of the identified compounds (based on modified characters of a previous study) and their chemical nature (multistate character, either as alkylphenol, benzoquinone or vinyl-ketone) on a modified Gonyleptidae phylogeny. Our results corroborate previous studies that alkylphenol is the ancestral most condition, changing to benzoquinone in the ancestor of Gonyleptidae or even earlier in a grassatorean ancestor depending on the analysis. Vinyl-ketones are a synapomorphy of K92. We briefly discuss character codifications and use of weights of ASR analyses of specific compounds, which were inconclusive. 1-(6-isopropyl-3,4-dihydro-2H-pyran-2-yl) isobutanone is shared by both Gonyleptes species and described for the genus Sodreana Mello-Leitão, 1922. 1-(6-(1-methyl-propyl)3,4-dihydro-2H-pyran-2yl)2-methylbutanone and 4-methyl-1-hepten-3-one are also shared by both Gonyleptes species and described for Moreiranula saprophila. From a taxonomic standpoint, combinations of specific compounds might help to diagnose supraspecific groups but given our limited sample, such decision should be taken with care and further tested. Finally, 7-methyl-2-octanol is described for the first time in Gonyleptidae, emphasizing the chemical diverse nature in the K92 clade.