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First published online March 9, 2004
Journal of Experimental Biology 207, 1313-1321 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00849

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Chemical defense of an opilionid (Acanthopachylus aculeatus)

Thomas Eisner^1,*, Carmen Rossini², Andrés González² and Maria Eisner¹

¹ Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA
² Facultad de Química, Universidad de la República, Montevideo, Uruguay

View larger version (103K): [in a new window]   Fig. 1. (A,B) Vonones sayi (from Lake Placid, Florida, USA). The animal is shown in ventral view, first (A) with droplets of newly formed effluent at anterolateral corners of prosoma, then (B), moments later, after having dipped a foreleg into one of the droplets, in anticipation of using that leg to brush the liquid onto an enemy. (C,D) Acanthopachylus aculeatus. In the first stage of its defensive response (C), enteric fluid has accumulated to form two droplets on the lateral carapace channels (arrows). Moments later (D), yellow quinonoid secretion has been injected into the enteric fluid.

View larger version (117K): [in a new window]   Fig. 2. A. aculeatus. (A) Front end, in ventral view, showing the clefts (arrows) between coxae of legs 1 and 2 that convey the oral effluent to the gland openings. (B) Front end, in right lateral view, showing the gland opening (upper arrow), and the notch under it, by which the oral effluent and secretion are routed onto the carapace channel (lower arrow) (compare with Fig. 4). (C) Right carapace channel, laden with clear oral effluent. (D) Comparable to C, after secretion has been added to effluent. (E) Comparable to C, at the moment when a second dose of secretion (arrow) is being emitted from the gland opening into the fluid in the channel. (F,G) Transfer of defensive fluid from carapace channel to femur (arrow) of hindleg.

View larger version (112K): [in a new window]   Fig. 3. A. aculeatus. (A) Left gland, exposed by cutting away part of the carapace. (B) Rear view of male, showing the hindlegs with their femoral spurs. (C) Individual under attack by ants (Formica exsectoides), before having emitted its defensive fluid. (D) Ant in the process of cleaning itself, in response to exposure to the defensive effluent of the opilionid. (E,F) Individual being inspected and spurned by a wolf spider (Lycosa ceratiola).

View larger version (185K): [in a new window]   Fig. 4. A. aculeatus, scanning electron micrographs. (A) Lateral view, showing the gland opening (right arrow) and the carapace channel (middle and left arrows). (B,C) Close-up view of side of animal at base of legs 1 to 3. In B, the animal is tilted to expose the right-hand ventral surface of the animal, bringing into view the cleft (arrow) between the coxae of legs 1 and 2, along which the oral effluent is conveyed. In C, the gland opening (arrow) is shown in relation to the two spines (asterisks) projecting from the coxae of leg 2 that presumably help direct the oral fluid past the gland opening; the notch immediately behind the gland opening serves to convey the liquid onto the carapace channel.

View larger version (67K): [in a new window]   Fig. 5. Defensive fluid emission mechanism of A. aculeatus. (A) Ventral view; oral effluent (red) has been routed by way of the clefts between the coxae of legs 1 and 2 to the margins of the body. (B) Right-side view; the fluid is seen emerging from between legs 1 and 2 and flowing past the gland opening onto the carapace channel. (C) Quinonoid secretion (blue) has been ejected from the gland opening into the stream of oral effluent. (D) The mixture of oral effluent and secretion has accumulated on the carapace channel.