Please cite this article in press as: Habegger, M.L., et al., Feeding biomechanics and theoretical calculations of bite force in bull sharks (Carcharhinus leucas) during ontogeny. Zoology (2012), http://dx.doi.org/10.1016/j.zool.2012.04.007 ARTICLE IN PRESS G Model ZOOL-25314; No. of Pages 11 Zoology xxx (2012) xxx–xxx Contents lists available at SciVerse ScienceDirect Zoology journa l h o me pa g e: www . els evier.com/locate/zool Feeding biomechanics and theoretical calculations of bite force in bull sharks (Carcharhinus leucas) during ontogeny Maria L. Habegger a,∗ , Philip J. Motta a , Daniel R. Huber b , Mason N. Dean c a Department of Integrative Biology, University of South Florida, 4202 E. Fowler Ave, Tampa, FL 33613, USA b Department of Biology, University of Tampa, 401 W. Kennedy Blvd, Tampa, FL 33606, USA c Department of Biomaterials, Max Planck Institute of Colloids & Interfaces, Am Muehlenberg 1, D-14476 Potsdam, Germany a r t i c l e i n f o Article history: Received 30 January 2012 Received in revised form 9 April 2012 Accepted 23 April 2012 Keywords: Chondrichthyes Bite force Feeding performance Scaling a b s t r a c t Evaluations of bite force, either measured directly or calculated theoretically, have been used to investi- gate the maximum feeding performance of a wide variety of vertebrates. However, bite force studies of fishes have focused primarily on small species due to the intractable nature of large apex predators. More massive muscles can generate higher forces and many of these fishes attain immense sizes; it is unclear how much of their biting performance is driven purely by dramatic ontogenetic increases in body size versus size-specific selection for enhanced feeding performance. In this study, we investigated biting per- formance and feeding biomechanics of immature and mature individuals from an ontogenetic series of an apex predator, the bull shark, Carcharhinus leucas (73–285 cm total length). Theoretical bite force ranged from 36 to 2128 N at the most anterior bite point, and 170 to 5914 N at the most posterior bite point over the ontogenetic series. Scaling patterns differed among the two age groups investigated; immature bull shark bite force scaled with positive allometry, whereas adult bite force scaled isometrically. When the bite force of C. leucas was compared to those of 12 other cartilaginous fishes, bull sharks presented the highest mass-specific bite force, greater than that of the white shark or the great hammerhead shark. A phylogenetic independent contrast analysis of anatomical and dietary variables as determinants of bite force in these 13 species indicated that the evolution of large adult bite forces in cartilaginous fishes is linked predominantly to the evolution of large body size. Multiple regressions based on mass-specific standardized contrasts suggest that the evolution of high bite forces in Chondrichthyes is further corre- lated with hypertrophication of the jaw adductors, increased leverage for anterior biting, and widening of the head. Lastly, we discuss the ecological significance of positive allometry in bite force as a possible “performance gain” early in the life history of C. leucas. © 2012 Elsevier GmbH. All rights reserved. 1. Introduction Bite force, a measure of feeding performance, can have a pro- found effect on trophic ecology and consequently survival and fitness (Herrel and O’Reilly, 2006; Huber et al., 2006; Kolmann and Huber, 2009). Barring restrictions from gape size or prey capture performance limitation, larger absolute bite force allows a preda- tor to ingest a wider range of foods and therefore can be considered to confer a selective advantage. It is therefore pertinent to ask how such high performance develops, both during ontogeny and on an evolutionary scale. A straightforward way to increase bite force during develop- ment is to simply increase the overall size of the animal, as this ∗ Corresponding author. Tel.: +1 813 974 2878; fax: +1 813 974 3263. E-mail addresses: maluhabegger@hotmail.com, mhabegge@mail.usf.edu (M.L. Habegger). will also increase the cross-sectional area of feeding muscles, and therefore the maximum force produced. If changes in bite force and size during ontogeny are proportional (isometry), the increase in performance can be attributed to the animal simply getting big- ger. However, bite force may also scale faster (positive allometry) or slower (negative allometry) than overall growth of the body, through size-independent modifications to the anatomy and/or physiology of the feeding mechanism such as changes in jaw lever- age. Determining whether performance changes are rooted simply in growth or in restructuring of the feeding mechanism during growth can help us to understand the mechanistic bases for changes in trophic structure on multiple time scales. Unfortunately, the ecological consequences of isometric vs. allo- metric growth trajectories are difficult to demonstrate. Positive allometry of vertebrate bite forces has been commonly reported (Erickson et al., 2003; Herrel and Gibb, 2006; Huber et al., 2006), often in association with ontogenetic changes in diet (Wainwright, 1988; Hernandez and Motta, 1997; Erickson et al., 2003; Herrel 0944-2006/$ – see front matter © 2012 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.zool.2012.04.007