Does life in caves reduce the diversity of chemicals produced by the pygidial glands of carabids?

Abstract

Carabids have paired pygidial glands in the abdomen that produce a great diversity of chemicals. Adults of three cave-dwelling (both troglophilous and troglobite) ground beetles from southeastern Serbia were induced to discharge secretions of the pygidial glands into vials. Extraction with dichloromethane was used in order to obtain the secretions, and the compounds were identified by gas chromatography-mass spectrometry (GC-MS). The aims of the study were to identify the chemical contents of the released compounds, to check whether the underground way of life had influenced both composition of the secretions and the number of the pygidial chemicals, and to search for possible new compounds that have not previously been reported in Carabidae. Totally, 42 compounds were identified. Pheggomisetes ninae contained 32, Laemostenus (Pristonychus) punctatus 13, while Duvalius (Paraduvalius) milutini had nine glandular compounds. Caproic, oleic, palmitic and stearic acids were present in the samples of all analyzed species. Heptacosene and nonacosadienes were predominant in the pygidial extract in P. ninae. Undecane was the major component in the secretion of L. punctatus. The most abundant compound in D. milutini secretion was palmitic acid. The adaptation to underground life did not lead to a reduction or changes of chemical defense mechanism in all analyzed Platyninae and Trechinae taxa.