Motor Control Across Trophic Strategies: Muscle Activity of Biting and Suction Feeding Fishes

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Abstract
Many fishes use a powerful bite of the oral jaws to capture or tear their prey. This behavior has received less study from functional morphologists and physiologists than suction feeding, and presents an opportunity to examine motor control of fish feeding across alternative prey-capture strategies. We used electromyography to compare muscle activity patterns of the feeding bite in five teleost fishes representing at least three lineages in which biting has been independently acquired: two parrotfish (Cetoscarus bicolor and Scarus iseri), a wrasse (Cheilinus chlorourus), and two serrasalmines, a pacu (Piaractus brachypomus) and a piranha (Pygocentrus nattereri). Multivariate analysis indicated that muscle activity patterns differed significantly among species, although a four-way ANOVA designed to test for differences within a phylogenetic hierarchy revealed that the biting motor pattern was largely similar for both narrow and broad phylogenetic comparisons. A comparison of the motor patterns of biting and suction feeding species revealed that biters had significantly shorter durations of the epaxialis and sternohyoideus and significantly longer relative onset times of the epaxialis, adductor mandibulae, and sternohyoideus. Character mapping of timing variables suggested that short relative onset times are primitive for suction feeders and that this characteristic is generally retained in more advanced species. Despite these differences, all species overlap extensively in multivariate EMG space. Our results demonstrate that change in the feeding motor pattern has accompanied morphological and behavioral change in transitions from suction to biting, which suggests that the neuromotor system has not acted as a constraint on the evolution of the feeding system in fishes.