Modelling stress in the feeding apparatus of seahorses and pipefishes (Teleostei: Syngnathidae) HELEEN LEYSEN 1 *, ELIZABETH R. DUMONT 2 , LOES BRABANT 3 , LUC VAN HOOREBEKE 3 and DOMINIQUE ADRIAENS 1 1 Research Group Evolutionary Morphology of Vertebrates, Ghent University, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium 2 Department of Biology, University of Massachusetts, 221 Morrill Science Center, Amherst, MA 01003-9297, USA 3 UGCT, Department of Physics and Astronomy, Ghent University, Proeftuinstraat 86, B-9000 Gent, Belgium Received 24 March 2011; revised 20 May 2011; accepted for publication 20 May 2011bij_1733 680..691 Seahorses and pipefishes are extremely fast suction feeders, and the fast strikes probably result in large and rapid pressure drops in the buccal cavity. These rapid drops in pressure imply heavy mechanical loading on the cranium; hence, the feeding apparatus is thought to experience high levels of stress. We used finite element analysis (FEA) to investigate where stress accumulates under strong suction pressure, and whether there is a difference in craniofacial stress distribution between long- and short-snouted species. The expectation was that high stress levels would occur at the articulations and in the cartilaginous regions of the cranium, and that, given the same pressure, the skulls of long-snouted species would exhibit lower stress levels than the skulls of short-snouted species, as an evolutionary increase in snout length might have made these species structurally better adapted to deal with high suction pressures. The results partially support the first hypothesis: except for Dunckerocampus dactyliophorus, all models show peak stress concentrations at the articulations and cartilaginous regions. However, no simple relationship between snout length and the magnitudes of stress predicted by the FEA was found. In an attempt to explain this lack of a relationship, the methodology was evaluated by assessing the effect of hyoid position and model construction on the stress distribution. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104, 680–691. ADDITIONAL KEYWORDS: bone stress – finite element analysis – snout elongation – suction feeding. INTRODUCTION Among teleosts, the most widespread method of prey capture is suction feeding (Lauder, 1980, 1983, 1985; Muller & Osse, 1984; Carroll et al., 2004). Suction feeding involves a powerful expansion of the oral cavity that generates a negative pressure within the head relative to ambient pressure. This pressure gradient draws water with prey into the mouth to fill the additional space and thereby equalize the pressure (e.g. Alexander, 1969; Lauder, 1985; Sanford & Wainwright, 2002). Buccal expansion can be accom- plished by maxillary protrusion, depression of the lower jaw, lateral abduction of the suspensoria, neu- rocranial elevation, and depression of the hyoid (Alexander, 1969; Lauder, 1983). With prey capture times of less than 6 ms, pipe- fishes and seahorses (Syngnathidae) are the fast- est recorded suction feeders (Muller & Osse, 1984; Bergert & Wainwright, 1997; de Lussanet & Muller, 2007; Roos et al., 2009a). Explosive cranial kine- matics, such as extremely rapid accelerations of skeletal elements and high suction forces, are gener- ated during the powerful suction feeding of these fishes. A syngnathid feeding strike is characterized by a very fast depression of the hyoid and an almost *Corresponding author. E-mail: heleen.leysen@ugent.be Biological Journal of the Linnean Society, 2011, 104, 680–691. With 5 figures © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104, 680–691 680