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First published online October 17, 2008
Journal of Experimental Biology 211, 3378-3391 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.023564
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Biomechanics of a convergently derived prey-processing mechanism in fishes: evidence from comparative tongue bite apparatus morphology and raking kinematics

Nicolai Konow* and Christopher P. J. Sanford

Department of Biology, 114 Hofstra University, Hempstead, NY 11549, USA


Figure 1
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  		Fig. 1. Phylogeny for the `Ancient fishes' following Ishiguro et al. (Ishiguro et al., 2003Go) with trait-mapping to clades (maximum parsimony; Mesquite v. 2.01; http://mesquiteproject.org) identifying the presence of a cleithrobranchial ligament (CBL), a tongue bite (see text) and raking behavior. Morphology data (Sanford and Lauder, 1989Go; Sanford, 2001bGo); for TBA (Nelson, 1968Go; Greenwood, 1971Go; Rosen, 1974Go; Taverne, 1977; Taverne, 1978; Lauder and Liem, 1983Go; Hilton, 2001Go); behavioral data (Kershaw, 1976Go; Sanford and Lauder, 1989Go; Sanford and Lauder, 1990Go; Sanford, 2001aGo; Sanford, 2001bGo).

 

Figure 2
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  		Fig. 2. High-speed video image series from representative movie sequences of raking in O. mykiss and S. jardinii. The typical stages of a rake seen in each taxon are illustrated with their mean timing relative to t0 indicated (in ms) at the bottom left corner of each frame. The primary kinematic variables were calculated from motion analysis of the eight topographical points shown in A and G (see text for details). Kinematic displacement, indicated with yellow lines for angular and red lines for linear displacement, in each frame becomes apparent in the following frame. White arrows indicate displacement and grey arrows indicate subsequent variable recovery. O. mykiss: (A) preparatory phase (gape occlusion and lower jaw elevation); (B) t0 (onset of cranial elevation, followed by pectoral girdle retraction); (C) completion of cranial elevation; (D) completion of power stroke, followed by recovery phase (cranial depression and pectoral girdle protraction); (E) common pause in kinematics; (F) gape expansion and lower jaw angle recovery. S. jardinii: (G) preparatory phase (gape occlusion and lower jaw elevation); (H) preparatory cranial depression; (I) t0 (onset of cranial elevation and hyoid elevation); (J) pectoral girdle retraction, to completion of power stroke; (K) recovery phase initiated by cranial depression and pectoral girdle protraction; (L) gape expansion.

 

Figure 3
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  		Fig. 3. Diagrammatic illustration of tongue-bite apparatus (TBA) in salmonid and osteoglossomorph fishes showing (A) medial TBA components and musculature driving the power stroke in O. mykiss, (B) left lateral components of the TBA and musculature involved in the preparatory phase of raking in O. mykiss and (C) medial TBA components and musculature driving the power stroke in S. jardinii. In A and C, the darkest grey indicates the directly opposed TBA dentition relevant to this study. In B, the left lateral mandible and preoperculum bones are only outlined to expose medial structures; the lateral-most of which is the dark-shaded suspensorium. Muscle and bone labeling is derived from Rosen, Sanford and Hilton (Rosen, 1974Go; Sanford, 2000Go; Hilton, 2003Go). Muscles: SH, m. sternohyoideus; PH, m. protractor hyoideus; AM, m. adductor mandibularis; EP, m. epaxialis; HP, m. hypaxialis. Ligaments: CBL, cleithrobranchial ligament; LAM, ligament of the AM inserting onto the mandible; LSH, ligament of the SH inserting onto the hyoid. Bones: ba3, 3rd branchial arch; bb1–5, basibranchials 1–5; bb*, fused basibranchial 2–5, forming the basihyal tooth plate foundation; bh; basihyal; bhtp, basihyal tooth plate; cha, anterior ceratohyal; chp, posterior ceratohyal; cl, cleithrum; co, coracoid; dpl, dermopalatine; ecp, ectopterygoid; enp, endopterygoid; enptp, endopterygoid tooth plate; hhd, dorsal hypohyal; hhv, ventral hypohyal; h, hyomandible; ihy, interhyal; m, mandible; mpt, metapterygoid; nc, neurocranium; pas, parasphenoid; pop, preoperculum; pmx, premaxilla; pfb, pectoral fin base; pfm, pectoral fin muscle; prhb2, process on 2nd hypobranchial; prhb3, process on 3rd hypobranchial; pt, posttemporal; q, quadrate; s, symplectic; scl, supracleithrum; uh, urohyal; v, vertebral column.

 

Figure 4
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  		Fig. 4. Mean profile plots for four derived kinematic variables during raking on goldfish prey in O. mykiss and S. jardinii. (A) Gape distance excursion; (B) hyoid distance; (C) cranial elevation; (D) pectoral girdle retraction. Triangles, O. mykiss; circles, S. jardinii. t0=onset of cranial elevation. Note that jaw adduction remains constant in S. jardinii while in O. mykiss hyoid movements are more pronounced.

 

Figure 5
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  		Fig. 5. Scatter plot of PC2 and PC3 from a principal component analysis on kinematic timing and magnitude data (Table 2) associated with O. mykiss and S. jardinii raking. Eigenvectors represent significant component loading values (Table 3), scaled to PC1 axis length, for the following variables: NEA, cranial elevation amplitude; PGA, pectoral girdle retraction amplitude; PGT, pectoral girdle retraction timing; HA, hyoid distance amplitude; GDT, gape distance timing.

 

Figure 6
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  		Fig. 6. Scatter plot of PC1 and PC2 from a principal component analysis on kinematic timing and magnitude data (Table 2) associated with behaviors: raking (green crosses) in O. mykiss and S. jardinii, and chewing (orange crosses) and strikes (red circles) in all taxa. Eigenvectors as in Fig. 5. NEA, cranial elevation amplitude; NET, cranial elevation timing; HA, hyoid distance amplitude; HT, hyoid distance timing; PGA, pectoral girdle retraction amplitude; PGT, pectoral girdle retraction timing; GDA, gape distance amplitude; GDT, gape distance timing. Note that while cranial elevation amplitude loaded most strongly along PC3 (not shown), its vector plane was identical to that shown in the PC1–2 plot.

 

Figure 7
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  		Fig. 7. Biomechanical models of cranial structures directly involved in raking, developed using morphological and kinematic evidence from O. mykiss and S. jardinii. Muscles are indicated with red lines, heavy when muscle contraction is inferred. (A,B) Raking preparatory phase, involving basihyal protraction, elicited by the PH muscle, and lower jaw occlusion, elicited by AM contraction. Three raking power-stroke pathways were derived from results in this and previous studies: (C,D) cranial elevation elicited by EP muscle contraction (with the BH anchored by the CBL to the cleithrum, held fixed by HP and/or regionally specialized EP musculature) and explained by a third-order lever system (black bars; heavy grey broken line in D indicates the initial position of this lever); (E,F) pectoral girdle retraction elicited by HP muscle contraction [the CBL (blue) and SH linking pectoral girdle and BH] described by a planar four-bar linkage [black quadrilateral; I, input linkage (EP); F, fixed lever (neurocranium); O, opening lever (TBA gape); C, coupler linkage (CBL and SH) (heavy grey broken quadrilateral in F indicates the initial position of this linkage)]; (G,H) basihyal retraction directly elicited by SH contraction (where the CBL plays no direct role). Abbreviations: SH, m. sternohyoideus; PH, m. protractor hyoideus; AM, m. adductor mandibularis; EP, m. epaxialis; HP, m. hypaxialis; CBL, cleithrobranchial ligament; nc, neurocranium; chy, ceratohyal; pg, pectoral girdle; sus, suspensorium; bh, basihyal; v, vertebral column; d, dentary; p, prey.

 

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