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First published online June 11, 2007
Journal of Experimental Biology 210, 2057-2069 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02779

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Are ontogenetic shifts in diet linked to shifts in feeding mechanics? Scaling of the feeding apparatus in the banded watersnake Nerodia fasciata

Shawn E. Vincent^1,2,*, Brad R. Moon³, Anthony Herrel⁴ and Nathan J. Kley²

¹ Department of Zoology, Ethology Laboratory, Kyoto University, Kitashirakawa Oiwakecho Sakyo Kyoto, 606-8502, Japan
² Department of Anatomical Sciences, Health Sciences Center, T8 (069), Stony Brook University, Stony Brook, NY 11794-8081, USA
³ Department of Biology, University of Louisiana at Lafayette, Lafayette, LA 70504-2451, USA
⁴ Biology Department, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium

View larger version (35K): [in this window] [in a new window]   Fig. 1. Anatomical illustrations of (A) the cranial bones and (B) jaw-closing levers that were examined in banded watersnakes (Nerodia fasciata).

View larger version (57K): [in this window] [in a new window]   Fig. 2. The cranial muscles that were examined in banded watersnakes (Nerodia fasciata). Note that some additional cranial muscles not examined here have been included in this illustration. The illustration was drawn using a Wild Heerbrug (M3Z) binocular microscope with camera lucida. (A) Lateral view of the superficial adductor mandibulae muscle group. (B) Lateral view of cranium with the m. adductor externus profundus (AEP) removed to expose the m. adductor posterior (not measured here). (C) Lateral deep view of the cranium showing the deeper muscles of the adductor mandibulae group.

View larger version (12K): [in this window] [in a new window]   Fig. 3. Plot of principal component 1 (x-axis) versus principal component 2 (y-axis) showing the size and shape differences between the most commonly consumed fish and frog prey of banded watersnakes (Nerodia fasciata). Overall, the frogs (green circles) consumed by these snakes are significantly more massive and wider than most fish (blue circles; see Results). See Table 2 for variable loadings.

View larger version (15K): [in this window] [in a new window]   Fig. 4. The relationships between gape, cranial bone lengths and head length in banded watersnakes (Nerodia fasciata). The dotted lines indicate the slope predicted under a model of geometric similarity (length=1, area=2). Closed circles indicated individuals <500 mm snout–vent length (SVL) that almost exclusively consume fish, and open circles indicate individuals >500 mm SVL that almost exclusively consume frogs.

View larger version (4K): [in this window] [in a new window]   Fig. 5. The relationship between jaw-closing mechanical advantage (MA) (based on the residuals of log10-transformed data as described in the text) and head length in banded watersnakes (Nerodia fasciata). The solid line indicates the empirical slope calculated using reduced major axis regression. This slope did not significantly differ from 0 (Table 4). Closed circles indicated individuals <500 mm snout–vent length (SVL) that almost exclusively consume fish, and open circles indicate individuals >500 mm SVL that almost exclusively consume frogs.

View larger version (25K): [in this window] [in a new window]   Fig. 6. The relationships between muscle physiological cross-sectional areas (pCSA) and head length in banded watersnakes (Nerodia fasciata). Dotted lines indicate the slope predicted under a model of geometric similarity (area=2). All slopes were significantly greater than the predicted value of 2 (Table 4). Closed circles indicated individuals <500 mm snout–vent length (SVL) that consume fish almost exclusively and open circles indicate individuals >500 mm SVL that consume frogs almost exclusively. Add. Ex. Sup., adductor externus superficialis; Add. Ex. Med., adductor externus medialis; Ret. Quad., retractor quadratri; Add. Ext. Prof., adductor externus profundus; Prot. Pter., protractor pterygoidei; D. mandibulae, depressor mandibulae; Ret. Pter., retractor pterygoidei.