Chrysomelidial in the Opisthonotal Glands of the O

Authors: Günther Raspotnig Rene Kaiser Edith Stabentheiner HansJörg Leis

Publish Date: 2008/07/10

Volume: 34, Issue: 8, Pages: 1081-

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Abstract

Gas chromatographic–mass spectrometric analyses of whole body extracts of Oribotritia berlesei a largesized soildwelling oribatid mite revealed a consistent chemical pattern of ten components probably originating from the welldeveloped opisthonotal glands The three major components of the extract were the iridoid monoterpene 3S8Schrysomelidial about 45 of the extract the unsaturated hydrocarbon 69heptadecadiene and the diterpene βspringene the latter two each about 20–25 of the extract The remaining minor components together about 10 of the extract included a series of hydrocarbons tridecene tridecane pentadecene pentadecane 8heptadecene and heptadecane and the tentatively identified 917octadecadienal In contrast analysis of juveniles showed only two compounds namely a 21 mixture of 3S8Schrysomelidial and its epimer epichrysomelidial 3S8Rchrysomelidial Unexpectedly neither adult nor juvenile secretions contained the socalled astigmatid compounds which are considered characteristic of secretions of oribatids above moderately derived Mixonomata The chrysomelidials as well as βspringene and octadecadienal are newly identified compounds in the opisthonotal glands of oribatid mites and have chemotaxonomic potential for this group This is the first instance of finding chrysomelidials outside the ColeopteraThe largest and most conspicuous exocrine system in the acariform mite suborders Oribatida and Astigmata is the paired opisthonotal glands syn oil glands These glands according to a current and widely accepted hypothesis evolved only once within ancient Oribatida after the nearbasal oribatid groups Palaeosomata and Enarthronota had splitoff and are considered characteristic of the four morederived oribatid groups Parhyposomata Mixonomata Desmonomata Brachypylina and also of astigmatid mites The presence of opisthonotal glands not only constitutes a major argument for a proposed monophyletic unit of socalled glandulate Oribatida including Astigmata Norton 1998 but also provides evidence for the evolutionary origin of astigmatid mites in an ancient opisthonotal glandbearing oribatid groupIn addition to the presence or absence of opisthonotal glands the secretions of these glands provide phylogenetic information as they include a rich variety of hydrocarbons terpenes aromatics and alkaloids in speciesspecific or groupspecific patterns These secretions derived from a homologous gland system allow the tracing of evolutionary lineages from nearbasal to morederived glandulate Oribatida Apart from the wellstudied opisthonotal gland secretions of Astigmata Kuwahara 2004 the secretions of a selection of species of several major groups of glandulate oribatids have been investigated including representatives of Parhyposomata Sakata and Norton 2001 a few species of Mixonomata and Desmonomata Sakata et al 1995 2003 Raspotnig et al 2001 2005a b Shimano et al 2002 Sakata and Norton 2003 and also examples of Brachypylina Takada et al 2005 Saporito et al 2007 While Parhyposomata produce phenols and naphthols the socalled astigmatid compounds sensu Sakata and Norton 2001 evolved within ancient mixonomatans and hence are possibly found in all the above groups These astigmatid compounds comprise a set of terpenes and aromatics namely neral geranial neryl formate 2hydroxy6methylbenzaldehyde and γacaridial The distribution of astigmatid compounds in oribatids is of special interest since these compounds not only provide chemical support for the evolutionary origin of astigmatid mites within ancient Oribatida Norton 1998 but also define a presumably monophyletic subunit within glandulate Oribatida the “astigmatid compoundsbearing” oribatids Raspotnig 2006Several chemotaxonomic studies that examined these presumptive astigmatid compoundbearing groups have been undertaken and have yielded a fragmented picture of the distribution of astigmatid compounds These compounds are difficult to detect in the more derived groups of Desmonomata apart from Trhypochthoniidae and generally in Brachypylina suggesting that in these groups astigmatid compounds have been prone to evolutionary reduction and replacement In some cases desmonomatan and brachypyline species are chemically “dimorphic” with astigmatid compounds present only in juveniles and completely replaced in adults by novel compounds such as toxic alkaloids Takada et al 2005 Saporito et al 2007 In contrast the full or nearly full set of astigmatid compounds seems to characterize highly derived mixonomatans low to moderately derived representatives of Desmonomata and Astigmata Specifically these compounds have been detected in opisthonotal gland secretions of Collohmannia gigantea Raspotnig et al 2001 in all Trhypochthoniidae so far investigated eg Sakata et al 1995 2003 and in astigmatid mites eg Kuwahara 2004 However there are large gaps in our knowledge of the distribution of astigmatid compounds the most conspicuous gap being in the Euphthiracaroidea a speciose group of box mites whose opisthonotal gland chemistry has yet to be investigated Euphthiracaroids are considered a group of highly derived mixonomatans that together with phthiracaroids constitute a possible sister group of Collohmannia Thus euphthiracaroids are likely candidates for producing astigmatid compounds The study of the chemistry of opisthonotal glands in euphthiracaroids is important not only to further our understanding of the evolution of astigmatid compounds but also because this group is a crucial link for tracing a possible evolutionary lineage from Oribatida to Astigmata With respect to the latter some not all recent molecular studies eg Murell et al 2005 Domes et al 2007 conflict with morphological data Therefore studying the opisthonotal gland chemistry may resolve this problemSpecimens of O berlesei Michael 1898 mixonomatan Oribatida Euphthiracaroidea Oribotritiidae were collected from the litter and fermentation layer of a mixed forest near Ferlach Carinthia Austria Individuals were collected by hand or extracted from soil samples by using BerleseTullgren funnels In all 35 adults all in the course of one collection in September 2006 were used for chemical analyses five adults were used for scanning electron microscopy and 30 adults were transferred to Petri dishes equipped with Plaster of Paris and dead wood and kept in the dark for a period of about 12 months either at room temperature one Petri dish or at 10°C second Petri dish respectively Individuals of both Petri dishes laid eggs and the offspring were reared to deutonymphal and tritonymphal instars Since immatures are burrowers in dead wood pieces of dead wood provided in the rearing dishes were checked for immatures at weekly intervals Ten deutonymphs and eight tritonymphs were used in the chemical studiesExtracts containing opisthonotal gland secretions of adults were prepared by immersing freshly collected living individuals in hexane one individual per 100 μl for 30 min Raspotnig et al 2001 2005a b For juveniles individual and pooled extracts containing two to six individuals were prepared similarly The extracts were used without further cleanupA trace gas chromatograph GC coupled to a Voyager mass spectrometer MS both from Thermo Vienna Austria and equipped with a ZB5MS fused silica capillary column 30 m × 025 mm id 025 μm film thickness Phenomenex Germany was used for the analyses Injection was splitless with helium at a constant flow rate of 15 ml min−1 as a carrier gas The column temperature was programmed from 50°C held for 1 min to 200°C at 10°C min−1 and then to 300°C at 15°C min−1 The ion source of the mass spectrometer and the transfer line were kept at 150°C and 310°C respectively Electron impact EI spectra were recorded at 70 eV

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