Scent gland chemistry and chemosystematics in harvestmen

Abstract

This review focuses on advances in opilionid scent gland research between the years 2005 and 2012, along with an evaluation of all currently available chemical information from different groups of Opiliones from a phylogenetic perspective. To date, examples of scent gland secretions from all four suborders of Opiliones have been published, including: 4 species of Cyphophthalmi, 12 species of Eupnoi, 1 species of Dyspnoi, 4 species of insidiatorean Laniatores, and 42 species of grassatorean Laniatores. In addition, preliminary data are given for another 20 species (mainly Insidiatores and Eupnoi). From all species, more than 70 scent gland-derived components from different chemical classes have so far been identified. Secretion profiles appear to be highly specific, and well-suited for both the characterization of phyletic groups as well as for the distinction of closely related species. Secretions may contain more than 20 components (e.g. Cyphopththalmi), or consist of only a few, or even a single compound (e.g. some Insidiatores and early-derivative Grassatores). With respect to gross systematics, the suborders of Opiliones can be chemically characterized as follows: naphthoquinones and acyclic compounds (mainly ketones) appear to be widespread in the secretions of a proposed clade of Cyphophthalmi + Palpatores (Eupnoi, Dyspnoi). For this clade, naphthoquinones are considered synapomorphic, since they have not been detected in the laniatores. Although the phyletic status of acyclic compounds in cyphophthalmid and palpatorean secretions remains unclear, these acycles may also have a common origin. A sub-class of these acycles, the so-called “sclerosomatid compounds”, may represent a chemical synapomorphy of the monophyletic Palpatores. Deep chemical divergence is evident in secretions from the Laniatores, along with a split of laniatorean secretions into at least two chemically distinct groups: travunioid Insidiatores mainly produce an array of nitrogen-containing compounds, whereas phenol- and benzoquinone-rich secretions are characteristic of grassatorean Laniatores. However, a link between the chemistry of laniatoreans and the secretions of Cyphophthalmi-Palpatores is still missing.