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First published online November 5, 2004
Journal of Experimental Biology 207, 4283-4289 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01241

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Rumen metabolites serve ticks to exploit large mammals

Gérard Donzé, Conor McMahon and Patrick M. Guerin^*

Institute of Zoology, University of Neuchâtel, Rue Emile-Argand 11, 2007 Neuchatel, Switzerland

View larger version (10K): [in a new window]   Fig. 1. Attraction of A. variegatum to rumen fluid odour. Polar plots of the mean walking direction of 18 A. variegatum adults presented in three successive 1 min intervals with (A) a control air stream (0°), (B) rumen fluid odour in the air stream and (C) the control air stream (without rumen fluid) again. Ticks that spent more time walking in the cone delimited by 60° either side of upwind (in red) after presentation of the rumen odour were considered to be attracted. (D) A track described by an A. variegatum adult in the same experiment; the track started (filled circle) with the tick walking down or across wind in the control period; the arrows on the track indicate stimulus on and off; the bar represents a displacement of 20 cm. Note the local search behaviour induced in A. variegatum by withdrawal of the rumen odour from the air stream. Open arrow at bottom indicates airstream direction (0°) for A,B,C and D.

View larger version (48K): [in a new window]   Fig. 2. Identification of rumen volatiles that stimulate olfactory receptor cells of ticks. Cattle rumen volatiles were analysed after collection on a porous polymer by gas chromatography coupled with electrophysiology recordings from olfactory receptor cells in wall-pore olfactory sensilla on the first leg tarsus of Amblyomma variegatum and Ixodes ricinus. (A) Flame ionisation detector (FID) response of the gas chromatograph to the separated rumen volatiles. (B) Enlarged sections of A where butanoic (A1), isopentanoic (A2), pentanoic (A3) and hexanoic (A4) acids, 2-nitrophenol (P1), 4-methyl-2-nitrophenol (P2), 4-methylphenol (P3), indole (I1) and 3-methylindole (I2) eluted and induced electrophysiological (EL) responses from olfactory receptor cells of A. variegatum and I. ricinus (trace for A. variegatum presented). The receptor cell response profiles in B were generated by summing the frequencies of the action potentials of the responding sensory cells (frequency to voltage conversion). U indicates an unidentified stimulus. (C,D) The spike trains generated in responding (from the arrows) A. variegatum (C) and I. ricinus (D) receptor cells to 4-methylphenol, butanoic acid and indole eluting from the gas chromatographic column. Receptor cells from both tick species also responded to acetic acid, propionic acid, phenol and 2-methylphenol (data not presented). The same carboxylic acid and phenolic volatiles identified in rumen odour of cattle were also recovered in the odour of roe deer rumen. Sensillum identity (DI and DII types) is according to a classification by Hess and Vlimant (1982).

View larger version (15K): [in a new window]   Fig. 3. Microbial production of volatile rumen products perceived by ticks.