Identification of Cuticular and Web Lipids of the Spider Argiope bruennichi

Abstract

Emerging evidence shows that the cuticular and silk lipids of spiders are structurally more diverse than those of insects, although only a relatively low number of species have been investigated so far. As in insects, such lipids might play a role as signals in various contexts. The wasp spider Argiope bruennichi has probably the best investigated chemical communication system within spiders, including the known structure of the female sex pheromone. Recently we showed that kin-recognition in A. bruennichi could be mediated through the cuticular compounds consisting of hydrocarbons and, to a much larger proportion, of wax esters. By use of mass spectrometry and various derivatization methods, these were identified as esters of 2,4-dimethylalkanoic acids and 1-alkanols of varying chain lengths, such as tetradecyl 2,4-dimethylheptadecanoate. A representative enantioselective synthesis of this compound was performed which proved the identifications and allowed us to postulate that the natural enantiomer likely has the (2R,4R)-configuration. Chemical profiles of the silk and cuticular lipids of females were similar, while male cuticular profiles differed from those of females. Major components of the male cuticular lipids were tridecyl 2,4-dimethyl-C_17-19 alkanoates, whereas those of females were slightly longer, comprising tridecyl 2,4-dimethyl-C_19-21 alkanoates. In addition, minor female-specific 4-methylalkyl esters were detected.

Keywords: Branched fatty acids; GC/MS; Kin-recognition; Pheromones; Wax esters.

Fig. 1

Microreactions performed with A. bruennichi extracts. Transesterification with TMSH transformed the wax esters into methyl esters that were again transesterified with 3-pyridinylmethanol or transformed into nicotinates with nicotinic acid

Fig. 2

Total ion chromatograms of the combined cuticular extracts from male (A) and female (B) A. bruennichi. *Octadecane as internal standard for quantification

Fig. 3

Discriminant analyses of cuticular extracts from males and females, as well as web silk from females, based on all peaks > 1% (A), only hydrocarbons (B), and only wax esters (C). Values in parentheses behind discriminant functions give percentages of explained variance

Fig. 4

Mass spectrum and structures of 2,4-dimethylalkyl wax ester mixture with I 3273

Fig. 5

Mass spectra of methyl 2,4-dimethylheptadecanoate (a), 3-pyridinylmethyl 2,4-dimethylheptadecanoate (b), and 4-methylheptadecyl nicotinate (c), derived from wax esters

Fig. 6

Synthesis of tetradecyl (2S,4S)-2,4-dimethylheptadecanoate (10). Please note that the configurational prefixes change during the synthesis due to the CIP-rules

Fig. 7

Resolution of the methyl ester of 2,4-dimethylheptadecanoic acid (9) on a chiral GC phase. Separation was performed using a Hydrodex β-6TBDM phase (30.0 m × 0.25 mm, 1.5 mL/min H₂, initial temp. 50 °C then 10 °C min⁻¹ to 125 °C holding time for 240 min, then with 10 °C min⁻¹ to final temp. 230 °C). A: methyl ester of synthetic (2S,4S)-2,4-dimethylheptadecanoic acid (9). B: methyl ester of the transesterified sample of a body extract of male Argiope bruenichi. C: same with female A. bruenichi