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First published online January 5, 2005
Journal of Experimental Biology 208, 233-248 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01357

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Non-olfactory chemoreceptors in asymmetric setae activate antennular grooming behavior in the Caribbean spiny lobster Panulirus argus

Manfred Schmidt^* and Charles D. Derby

Department of Biology and Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA 30302-4010, USA

View larger version (28K): [in a new window]   Fig. 1. Experiment 1. Effect of the bilateral selective removal of the lateral guard setae (GS) and the following bilateral selective removal of the asymmetric setae (AS) on the mean wipe rate of the antennules after stimulation with 3 ml of 0.5 mmol l–1 L-glutamate. Wipe rate values are means ± S.E.M. of N=8 experimental animals (Panulirus argus) over the 9 trials of an experimental 3-day block; experimental days are numbered chronologically. Note that selective removal of lateral GS does not cause a decrease in the mean wipe rate (Days 07–09) compared to the mean wipe rate measured in the unoperated animals in the initial 3-day block (Days 01–03). Note further the almost total loss of antennular wiping after selective removal of the AS (Days 11–13) and the small but constant functional recovery of wiping after longer time periods (Days 35–37, Days 49–51, Days 56–58). ANOVA shows an overall statistically significant difference between the columns (P<0.0001). Pair-wise comparisons by Newman–Keuls post tests between the means of the 3-day blocks reveal no significant difference between the pre-ablation (Days 01–03) and the post-GS-ablation (Days 07–09) blocks (P>0.05), whereas the post-AS-ablation block (Days 11–13) differs significantly (P<0.001) from the pre-AS-ablation block (Days 07–09) and from the retest blocks following after longer time periods (P<0.05 for all three blocks). Wipe rates of all 3-day blocks (means ± S.E.M.): Days 01–03, 13.3±2.6; Days 07–09, 16.4±1.5; Days 11–13, 0.5±0.2; Days 35–37, 2.6±0.7; Days 49–51, 2.3±0.6; Days 56–58, 3.8±0.8.

View larger version (128K): [in a new window]   Fig. 2. Examples of the efficiency of selective sensillar shaving. Light micrographs. (A) Lateral guard setae selectively removed. Every annulus bears two rows of aesthetascs (AE) and one asymmetric seta (AS) at their lateral edge. Medial guard setae (GS); companion setae (CS). (B) Lateral guard setae and asymmetric setae selectively removed (animal from Exp. 1). Every annulus bears two rows of aesthetascs (AE), some of which are damaged (asterisks) either by the shaving procedure or due to natural causes. Of asymmetric setae, only some stumps remain (arrows). Medial guard setae (GS). (C) Medial guard setae and aesthetascs selectively removed (animal from Exp. 2). Of the aesthetascs, only bases remain (asterisk). Every annulus bears one asymmetric seta (AS) with some exceptions where the AS either has been eliminated accidentally (arrow) when shaving the aesthetascs or was lost by natural causes. Lateral guard setae (GS).

View larger version (30K): [in a new window]   Fig. 3. Experiment 2. Effect of the bilateral selective removal of the aesthetascs (AE) and the medial guard setae (GS) on the mean wipe rate of the antennules after stimulation with 3 ml of 0.5 mmol l–1 L-glutamate. Wipe rate values are means ± S.E.M. of N=8 experimental animals (Panulirus argus) over the 9 trials of an experimental 3-day block; experimental days are numbered chronologically. Note that selective removal of the aesthetascs (together with the medial GS) does not cause a decrease in the mean wipe rate (Days 06–08) compared to the mean wipe rate measured in the unoperated animals in the initial 3-day block (Days 01–03). Note further that the mean wipe in the re-test blocks following after longer time intervals (Days 15–17, Days 22–24) is substantially higher than in the first two 3-day blocks of the experiment. ANOVA shows an overall statistically significant difference between the columns (P=0.002). Pair-wise comparisons by Newman–Keuls post tests between the means of the 3-day blocks reveal no significant difference between the pre-AE-ablation (Days 01–03) and the post-AE-ablation (Days 06–08) blocks (P>0.05), whereas the retest blocks following after longer time periods differ significantly from the post-AE-ablation block (P<0.01 for Days 15–17, P<0.05 for Days 22–24). The two retest blocks do not differ significantly from each other (P>0.05). Wipe rates of all 3-day blocks (means ± S.E.M.): Days 01–03, 10.0±1.2; Days 06–08, 11.4±1.5; Days 15–17, 20.7±3.9; Days 22–24, 18.4±1.9.

View larger version (26K): [in a new window]   Fig. 4. Experiment 3. Direct comparison of the effect of the bilateral selective removal of the asymmetric setae (AS) and the lateral guard setae (left side) vs the bilateral selective removal of the aesthetascs (AE) and the medial guard setae (right side) on the mean wipe rate of the antennules after stimulation with 3 ml of 0.5 mmol l–1 L-glutamate. Wipe rate values are means ± S.E.M. of N=6 experimental animals (Panulirus argus) in each experimental group over the 9 trials of an experimental 3-day block; experimental days are numbered chronologically. Note that selective removal of the AS (Days 08–10, left) is followed by an almost total loss of antennular wiping, whereas selective removal of the AE (Days 08–10, right) causes no decrease in the mean wipe rate compared to the mean wipe rate measured in the unoperated animals in the initial 3-day block (Days 01–03). Pair-wise comparisons by paired t-tests between the means of the 3-day blocks reveal a significant difference between the pre-AS-ablation (Days 01–03, left) and the post-AS-ablation (Days 08–10, left) blocks (P<0.01), but not between the pre-AE-ablation block (Days 01–03, right) and the post-AE-ablation block (Days 08–10, right) (P=0.82). Comparison between the post-AS-ablation and the post-AE-ablation block by an unpaired t-tests reveals a significant difference between them (P<0.0001). Wipe rates of all 3-day blocks (means ± S.E.M.): Days 01-03 AS-ablation, 17.7±4.1; Days 08–10 AS-ablation, 0.7±0.2; Days 01–03 AE-ablation, 16.8±3.0; Days 08-10 AE-ablation, 17.6±2.3.

View larger version (54K): [in a new window]   Fig. 5. Experiment 4. Direct comparison of the effect of the bilateral selective removal of the aesthetascs (AE) and the medial guard setae (lighter gray and hatched columns) vs the bilateral selective removal of only the medial guard setae (GS) (darker gray and cross-hatched columns) on the mean wipe rate of the antennules after stimulation with 3 ml of 0.5 mmol l–1 L-glutamate. Wipe rate values are means ± S.E.M. of N=7 experimental animals (Panulirus argus) in each experimental group over the 9 trials of an experimental 3-day bock; experimental days are numbered chronologically. Note that neither the selective removal of the AE (together with the medial GS) nor the selective removal of only the medial GS has any consistent, long-term effect on the mean wipe compared to the mean wipe rate measured in the unoperated animals in the initial 3-day block (Days 01–03). ANOVA shows no overall statistically significant difference between the columns in either experimental group (P=0.36 for AE+GS-ablated animals, P=0.80 for GS-ablated animals). Pair-wise comparisons by unpaired t-tests between the means of the respective 3-day blocks also reveal no significant differences between both treatments (P=0.81 for Days 08–10, P=0.74 for Days 13–15, P=0.88 for Days 20–22). Wipe rates of all 3-day blocks (means ± S.E.M.): Days 01–03, AE-ablation, 15.4±2.7; Days 01–03, GS-ablation, 19.6±3.1; Days 08–10, AE-ablation, 19.1±3.1; Days 08–10, GS-ablation, 17.9±3.3; Days 13–15, AE-ablation, 21.2±4.5; Days 13–15, GS-ablation, 19.2±3.4; Days 20–22, AE-ablation, 19.6±4.5; Days 20–22, GS-ablation, 20.5±3.3.

View larger version (161K): [in a new window]   Fig. 6. Outer morphology of asymmetric setae. Scanning electron micrographs (A,B,D,E) or light micrographs (C,F). (A,B) Overview of sensilla arrangement in the `tuft' region of the lateral flagellum of Panulirus argus. Each annulus (A) bears two rows of aesthetascs (AE) flanked by two guard setae (GS). Guard setae are accompanied by companion setae (CS) at their lateral margins. One asymmetric seta (arrow) is located between the lateral guard seta and the aesthetascs. (C–F) Structure of asymmetric setae. Asymmetric setae have a smooth, slender setal shaft with two kinks and a terminal pore. (C) The proximal kink in the shaft (arrow) occurs at about one third of the length and has an angle of about 13°. Scale bar, 100 µm. (D) The shaft of the asymmetric seta (AS) inserts in a narrow socket and protrudes within the rows of aesthetascs (AE), many of which are intentionally broken off in this preparation to reveal their extremely thin cuticle. Proximal kink in the shaft (arrow). (E,F) At the tip of the shaft, a terminal pore is present (arrowhead), positioned at the base of a shallow cuticular rim. (E) Terminal pore at higher magnification. Scale bar in inset, 1 µm. (F) Distal kink in the shaft (double-arrow). Scale bar, 10 µm.

View larger version (61K): [in a new window]   Fig. 7. Identification of a scolopale at the base of asymmetric setae. Confocal micrographs representing collapsed stacks of optical sections (green, autofluorescence of cuticle; red, phalloidin–AlexaFluor568). (A) Asymmetric seta of a spiny lobster several days after molting as seen in the transmitted light channel. Proximal kink in the shaft (arrow); distal kink in the shaft (double-arrow). (B) The same asymmetric seta as seen in the fluorescence channels. Cuticle autofluorescence clearly delineates the shaft and the socket of the asymmetric seta. Below the socket a phalloidin-positive tube-like structure, the scolopale, is located (arrowhead). Scale as in A. (C) Base region of the same AS at higher magnification. Note tight socket structure and strand-like substructure of scolopale. (D) Another AS of the same animal. Note the generally identical arrangement and the larger distance of the scolopale (arrowhead) to the socket. (E,F) Base of an AS of an animal 1 day after molting. The scolopale is located within the shaft ca. 20 µm distal to the socket (S). (F) Note strand-like substructure of scolopale. (G,H) Base of an AS on the new cuticle of an animal shortly before molting. The scolopale is located within the shaft ca. 20 µm distal to the socket (S). (H) Note strand-like substructure of scolopale.