Regeneration of Complex Oil-Gland Secretions and Its Importance for Chemical Defense in an Oribatid Mite
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Most oribatid mites possess a pair of opisthonotal exocrine glands that produce mostly complex, species-specific secretions. Such blends may contain more than 10 different compounds, but hardly anything is known about their primary biosynthesis or regeneration. I analyzed recovery of the 6 main components from the 11-compound secretion of the oribatid mite Archegozetes longisetosus Aoki, including the main chemical classes hydrocarbons, aromatics, and terpenes, during a 20-day time course after complete gland depletion. About 10 % of the original total secretion amount was restored after 24 hr, and after 2–6 days, the amount had reached the range of total amount observed in the control group. Most compounds were recovered at similar rates within the first 48 hr. An important exception was pentadecane, which was predominantly produced in the first few hours, suggesting that this compound is the main solvent of the secretion. Although relative amounts of the main compounds differed significantly over time, the complex profile of the whole secretion was stable and not confidently distinguishable among the sampling dates. The general recovery rate was high during the first 48 hr, about 25 times higher than in the remaining 18 days. The biological importance of this high initial investment was supported by predation experiments: the predacious rove beetle Stenus juno was first repelled after 48 hr when at least 25 % of secretions was restored.
KeywordsChemical defense GC/MS Biosynthesis Regeneration Oil-glands Archegozetes longisetosus Acari Oribatida
I thank Günther Raspotnig and Roy Norton for their comments, Paavo Bergmann for information on oil-gland ultrastructure, and Lars Koerner for providing Stenus juno specimens for predation experiments and comments on the manuscript. This study was funded by the German Science Foundation (DFG-Forschungsstipendium HE4593/3-1) and supported by the Styrian language exchange service POTSCHASN (represented by Anna Truck).
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