VAN WASSENBERGH, S.; AERTS, P.; HERREL, A.; ADRIAENS, D.; University of Antwerp, Belgium; University of Antwerp, Belgium; University of Antwerp, Belgium; Ghent University, Belgium: A forward dynamic model of mouth closing movements in clariid catfishes
Some species of Clariidae (air breathing catfishes) have developed extremely large (hypertrophied) adductor mandibulae muscles. As increased forces exerted by these enlarged muscles will cause higher accelerations of the lower jaw, this jaw adductor hypertrophy could have evolved to power faster mouth closure. In this study, a forward dynamic model of jaw closing is developed in order to evaluate the importance of jaw adductor hypertrophy on the speed of mouth closure. The model includes inertia, pressure and hydrodynamic drag forces onto the lower jaw, which is modelled as a rotating half-ellipse. Simulations are run for four clariid species showing a gradual increase in jaw adductor hypertrophy (Clarias gariepinus, Clariallabes longicauda, Gymnallabes typus and Channallabes apus). The model was validated with data from high-speed videos of prey captures of these species. The kinematic profiles of the fastest mouth closure from each species are well predicted by the model. Additionally, the model was used to compare the four species during a standardized mouth closure (30 mm skull length, 40� to 10� gape angle rotation). According to our model, species with jaw adductor hypertrophy are unable to close the mouth faster than the non-hypertrophied C. gariepinus. Higher angular velocities are reached during the first 5 ms of mouth closure only. Subsequently, lower maximal velocities of mouth closure are reached in the species with enlarged jaw muscles. As the rotational velocity of the lower jaw is coupled to a higher shortening velocity of the jaw muscle fibres in these species, this results in a faster drop of the force output due to the force-velocity relationship of muscle. Consequently, the benefits of the altered jaw apparatus in these clariids for fast jaw closure is limited to the initial phase of mouth closure.
