Abstract
The monophyly of a clade consisting of Astigmata and some of the glandulate Oribatida is supported by a synapomorphic set of five oil gland-derived secretion compounds (neral, geranial, neryl formate, 2-hydroxy-6-methylbenzaldehyde (=2,6-HMBD) and 2-formyl-3-hydroxybenzaldehyde (=gamma-acaridial)), known as ‘Astigmata compounds’. Another aromatic compound, 7-hydroxyphthalide, was reported for Astigmata and Oribatida, but is not known from any other source in nature. It was discussed whether this compound was a ‘natural’ part of oil gland secretions (and thus probably of phylogenetic significance) or an artifact. Here, we show that 7-hydroxyphthalide is the result of a post-extraction chemical transformation of gamma-acaridial, and not a natural compound of oil gland secretions. We compared time series of raw extracts from Archegozetes longisetosus stored at -20°C with extracts stored at +23°C and show that storage at room temperature conditions promotes the transformation. However, since this reaction is quantitatively coherent, summing the amounts of both components seems to be a suitable approximation for the quantity of gamma-acaridial in natural secretions, even if 7-hydroxyphthalide is found in the analyses.
Highlights
Most sarcoptiform mites possess a large pair of exocrine opisthonotal glands, commonly termed oil glands (Sakata and Norton, 2001)
These consisted of the 9 components already described by Sakata and Norton (2003), the additional heptadecane found by Raspotnig and Föttinger (2008) and tridecane as a newly discovered component
Compounds were identified as: 2,6HMBD (=2-hydroxy-6-methyl-benzaldehyde, peak a, 13% of whole secretion (=WS)), neral, geranial, neryl formate, γ-acaridial (=3hydroxybenzene-1,2-dicarbaldehyde; peak e, main component with 29% of WS), tridecane, pentadecene, pentadecane, heptadecadiene, heptadecene and heptadecane
Summary
Most sarcoptiform mites possess a large pair of exocrine opisthonotal glands, commonly termed oil glands (Sakata and Norton, 2001). The chemical composition and biological function of secretions from these glands have been well studied in Astigmata since the 1970s (reviewed in Kuwahara, 2004), and substantial knowledge of oribatid mite oil gland chemistry has accumulated in the last 15 years ISSN 2107-7207 (electronic) are mostly species-specific and highly reproducible, so it has been suggested that these profiles might be a valuable set of characters for phylogenetic inference (Sakata and Norton, 2001). It has been hypothesized that all oil-gland bearing sarcoptiform mites (Astigmata and Oribatida) form a monophyletic group (Norton, 1998), a hypothesis that is strongly supported by morphology and oil gland chemistry
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