Department of Ecology and Evolutionary Biology, Brown University, 80 Waterman Street, Providence, RI, 02912, USA.
Sci Rep. 2021 May 14;11(1):10334. doi: 10.1038/s41598-021-88828-x.
The axial musculature of fishes has historically been characterized as the powerhouse for explosive swimming behaviors. However, recent studies show that some fish also use their 'swimming' muscles to generate over 90% of the power for suction feeding. Can the axial musculature achieve high power output for these two mechanically distinct behaviors? Muscle power output is enhanced when all of the fibers within a muscle shorten at optimal velocity. Yet, axial locomotion produces a mediolateral gradient of muscle strain that should force some fibers to shorten too slowly and others too fast. This mechanical problem prompted research into the gearing of fish axial muscle and led to the discovery of helical fiber orientations that homogenize fiber velocities during swimming, but does such a strain gradient also exist and pose a problem for suction feeding? We measured muscle strain in bluegill sunfish, Lepomis macrochirus, and found that suction feeding produces a gradient of longitudinal strain that, unlike the mediolateral gradient for locomotion, occurs along the dorsoventral axis. A dorsoventral strain gradient within a muscle with fiber architecture shown to counteract a mediolateral gradient suggests that bluegill sunfish should not be able to generate high power outputs from the axial muscle during suction feeding-yet prior work shows that they do, up to 438 W kg. Solving this biomechanical paradox may be critical to understanding how many fishes have co-opted 'swimming' muscles into a suction feeding powerhouse.
鱼类的轴向肌肉在历史上一直被认为是产生爆发性游泳行为的动力源。然而，最近的研究表明，一些鱼类也利用它们的“游泳”肌肉产生超过 90%的吸力进食的力量。轴向肌肉能否为这两种机械上截然不同的行为提供高功率输出？当肌肉内的所有纤维都以最佳速度缩短时，肌肉的功率输出会增强。然而，轴向运动产生了肌肉应变的中侧梯度，这应该迫使一些纤维缩短得太慢，而另一些纤维缩短得太快。这个机械问题促使人们对鱼类轴向肌肉的传动装置进行研究，并发现了螺旋纤维取向，它可以在游泳时使纤维速度均匀化，但这种应变梯度是否存在，并成为吸力进食的一个问题？我们测量了蓝鳃太阳鱼（Lepomis macrochirus）的肌肉应变，发现吸力进食会产生一个纵向应变梯度，与运动的中侧梯度不同，这个梯度沿着背腹轴发生。在一个具有纤维结构的肌肉中，存在一个背腹向的应变梯度，这种结构被证明可以抵消中侧梯度，这表明蓝鳃太阳鱼在吸力进食时不应该能够从轴向肌肉中产生高功率输出——然而之前的研究表明，它们可以，最高可达 438 W kg。解决这个生物力学悖论对于理解许多鱼类如何将“游泳”肌肉转化为吸力进食的强大动力源可能至关重要。
