Mechanical performance of aquatic rowing and flying

Abstract

Aquatic flight, performed by rowing or flapping fins, wings or limbs, is a primary locomotor mechanism for many animals. We used a computer simulation to compare the mechanical performance of rowing and flapping appendages across a range of speeds. Flapping appendages proved to be more mechanically efficient than rowing appendages at all swimming speeds, suggesting that animals that frequently engage in locomotor behaviours that require energy conservation should employ a flapping stroke. The lower efficiency of rowing appendages across all speeds begs the question of why rowing occurs at all. One answer lies in the ability of rowing fins to generate more thrust than flapping fins during the power stroke. Large forces are necessary for manoeuvring behaviours such as accelerations, turning and braking, which suggests that rowing should be found in slow-swimming animals that frequently manoeuvre. The predictions of the model are supported by observed patterns of behavioural variation among rowing and flapping vertebrates.

“On the Fence” versus “All in”: Insights from Turtles for the Evolution of Aquatic Locomotor Specializations and Habitat Transitions in Tetrapod Vertebrates

“…Taxa that have recently invaded aquatic habitats, or that still make frequent use of terrestrial habitats, typically move their limbs with predominantly anteroposterior (i.e., fore-aft) oscillations that include distinct recovery and power strokes, producing a rowing motion that broadly resembles patterns retained from terrestrial kinematics (Davenport et al 1984;Fish 1996;Walker and Westneat 2000;Rivera and Blob 2010). However, taxa that have become highly specialized for life in water often show predominantly dorsoventral (i.e., up-down) oscillations of the limbs, producing flapping motions through which propulsive forces may be generated during both the up-and downstrokes (Vogel 1994;Walker and Westneat 2000;. Whereas rowing strokes have been shown to be advantageous for swimming that requires frequent turns and maneuvers, flapping has been found to be more energetically efficient than rowing regardless of swimming speed, providing an advantage for species that may need to conserve energy while swimming long distances (Walker and Westneat 2000).…”

“…However, taxa that have become highly specialized for life in water often show predominantly dorsoventral (i.e., up-down) oscillations of the limbs, producing flapping motions through which propulsive forces may be generated during both the up-and downstrokes (Vogel 1994;Walker and Westneat 2000;. Whereas rowing strokes have been shown to be advantageous for swimming that requires frequent turns and maneuvers, flapping has been found to be more energetically efficient than rowing regardless of swimming speed, providing an advantage for species that may need to conserve energy while swimming long distances (Walker and Westneat 2000).…”

“…Among tetrapods, such shapes are usually accompanied by elongation and flattening to produce a flipper shape that is often accentuated in the forelimbs Smith and Clarke 2014;Young and Blob 2015a). Whereas several advantages of flipper morphology and flapping kinematics among hyperspecialized swimmers have been identified (Walker and Westneat 2000, 2002a, 2002bWalker 2002), the mechanisms that may have facilitated such transitions have remained less clear. Moreover, though impacts of swimming style on locomotor maneuverability have been proposed (Walker and Westneat 2000), less perspective is available on the complementary locomotor component of stability.…”

“…Whereas several advantages of flipper morphology and flapping kinematics among hyperspecialized swimmers have been identified (Walker and Westneat 2000, 2002a, 2002bWalker 2002), the mechanisms that may have facilitated such transitions have remained less clear. Moreover, though impacts of swimming style on locomotor maneuverability have been proposed (Walker and Westneat 2000), less perspective is available on the complementary locomotor component of stability. Hydrodynamic stability is the ability to correct for external and self-generated disturbances during aquatic motion that can cause deviations from a given trajectory and, thereby, decrease locomotor efficiency (Webb 2002;Weihs 2002;Bartol et al 2003).…”

“…Moving off the fence: mechanisms facilitating evolutionary change in limb structure and control during aquatic hyperspecialization in turtles During aquatic locomotion, the use of flattened appendages as dorsoventrally flapping propulsors can facilitate continuous, energetically efficient thrust production that is advantageous for sustained, long-distance swimming (Vogel 1994;Walker and Westneat 2000, 2002a, 2002bWalker 2002). The potential for such hydrodynamic advantages is clear once flipper-like morphology and flapping motions are present; however, species that secondarily invade aquatic habitats typically begin that process with very different patterns of limb structure and control (Fish 1996).…”