Volatile and Semi-Volatile Organic Compounds May Help Reduce Pollinator-Prey Overlap in the Carnivorous Plant Drosophyllum lusitanicum (Drosophyllaceae).

Most carnivorous plants show a conspicuous separation between flowers and leaf-traps, which has been interpreted as an adaptive response to minimize pollinator-prey conflicts which will reduce fitness. Here, we used the carnivorous subshrub Drosophyllum lusitanicum (Drosophyllaceae) to explore if and how carnivorous plants with minimal physical separation of flower and trap avoid or reduce a likely conflict of pollinator and prey. We carried out an extensive field survey in the Aljibe Mountains, at the European side of the Strait of Gibraltar, of pollinating and prey insects of D. lusitanicum. We also performed a detailed analysis of flower and leaf volatile and semi-volatile organic compounds (VOCs and SVOCs, respectively) by direct thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) to ascertain whether this species shows different VOC/SVOC profiles in flowers and leaf-traps that might attract pollinators and prey, respectively. Our results show a low overlap between pollinator and prey groups as well as clear differences in the relative abundance of VOCs and SVOCs between flowers and leaf-traps. Coleopterans and hymenopterans were the most represented groups of floral visitors, whereas dipterans were the most diverse group of prey insects. Regarding VOCs and SVOCs, while aldehydes and carboxylic acids presented higher relative contents in leaf-traps, alkanes and plumbagin were the main VOC/SVOC compounds detected in flowers. We conclude that D. lusitanicum, despite its minimal flower-trap separation, does not seem to present a marked pollinator-prey conflict. Differences in the VOCs and SVOCs produced by flowers and leaf-traps may help explain the conspicuous differences between pollinator and prey guilds.

Improving the analytical flexibility of thermal desorption in determining unknown VOC samples by using re-collection.

The thermal desorption (TD) technique has long suffered from the 'one-shot' problem, whereby the entire sample is consumed in a single analysis, and thus no sample remains for repeated analysis. Recent developments in TD equipment allow for the quantitative re-collection of split samples during thermal desorption, which can be utilised for archiving or immediate analysis. However, the performance of TD systems for re-collecting different volatile organic compounds (VOCs) has rarely been demonstrated. This study provides a systematic investigation into the re-collection efficiency for over 90 VOCs on a TD unit under different conditions. An analytical method was developed based on multi-sorbent tubes and TD-GC/MS, which could quantitatively measure 92 VOCs with good sensitivity (method detection limit between 0.01 and 2 ng) and precision (< 10%). Satisfactory re-collection performance (recoveries within 100% ± 20%) was found for over 70 compounds under different split modes for multiple times, and the single (outlet) split mode was preferred in this regard, in order to avoid significant uncertainties in the results. Thermal labile, polar or reactive compounds such as alcohols and ketones were generally not compatible with re-collection, as they were either lost due to thermal decomposition or formed as system artefacts. In addition, bromochloromethane should not be used as an internal standard when performing sample re-collection, since it will experience significant loss during repeated analysis and lead to overestimation for corresponding compounds. Finally, the re-collection was tested with low-concentration field samples to resolve the unexpected water problem in analysis. Although higher uncertainties were expected in the re-collected samples, the results provided good information on overall concentration variations at the sampling site, thereby instilling confidence in the results obtained from the primary analysis.