Abstract
ABSTRACTMany suction-feeding fish use neurocranial elevation to expand the buccal cavity for suction feeding, a motion necessarily accompanied by the dorsal flexion of joints in the axial skeleton. How much dorsal flexion the axial skeleton accommodates and where that dorsal flexion occurs may vary with axial skeletal morphology, body shape and the kinematics of neurocranial elevation. We measured three-dimensional neurocranial kinematics in three species with distinct body forms: laterally compressed Embiotoca lateralis, fusiform Micropterus salmoides, and dorsoventrally compressed Leptocottus armatus. The area just caudal to the neurocranium occupied by bone was 42±1.5%, 36±1.8% and 22±5.5% (mean±s.e.m.; N=3, 6, 4) in the three species, respectively, and the epaxial depth also decreased from E. lateralis to L. armatus. Maximum neurocranial elevation for each species was 11, 24 and 37°, respectively, consistent with a hypothesis that aspects of axial morphology and body shape may constrain neurocranial elevation. Mean axis of rotation position for neurocranial elevation in E. lateralis, M. salmoides and L. armatus was near the first, third and fifth intervertebral joints, respectively, leading to the hypothesis of a similar relationship with the number of intervertebral joints that flex. Although future work must test these hypotheses, our results suggest the relationships merit further inquiry.
Highlights
For many suction-feeding fish, neurocranial elevation is an important motion for expanding the buccal cavity and generating suction (e.g. Schaeffer and Rosen, 1961; Carroll and Wainwright, 2006; Camp and Brainerd, 2014; Van Wassenbergh et al, 2015)
We report the 3D neurocranial kinematics of these strikes as measured by a joint coordinate system (JCS) placed at the axis of rotation (AOR), in order to make them directly comparable to those of L. armatus and E. lateralis
If we consider the maximum magnitude of cranial elevation observed for each species across all strikes, the pattern does match our expectations with bone area decreasing in the order E. lateralis, M. salmoides, L. armatus (Fig. 3) and maximum observed neurocranial elevation increasing in the order E. lateralis (11.1°), M. salmoides (23.8°) and L. armatus (36.5°)
Summary
For many suction-feeding fish, neurocranial elevation is an important motion for expanding the buccal cavity and generating suction (e.g. Schaeffer and Rosen, 1961; Carroll and Wainwright, 2006; Camp and Brainerd, 2014; Van Wassenbergh et al, 2015). The neurocranium elevates by rotating dorsally about a transverse axis relative to the body To produce this elevation, the vertebrae linked to the neurocranium must flex dorsally across one or more intervertebral joints (IVJs; this study includes the craniovertebral joint among the IVJs, unless otherwise noted). Received 6 June 2018; Accepted 23 July 2018 that vertebral morphology is modified for permitting high degrees of neurocranial elevation in some fish (Lesiuk and Lindsey, 1978; Lauder and Liem, 1981; Huet et al, 1999) Despite this interest in vertebral specializations, few studies have explored how the axial skeleton as a whole may affect neurocranial motions and, how the requirement of neurocranial elevation may influence body shape and axial skeletal structures
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