Department of Physics and Institute of Biophysics, National Chung Hsing University, Taichung 40227, Taiwan.
Department of Entomology, National Taiwan University, Taipei 10617, Taiwan.
J R Soc Interface. 2014 Aug 6;11(97):20140273. doi: 10.1098/rsif.2014.0273.
Males of Dytiscinae beetles use specialized adhesive setae to adhere to female elytra during underwater courtship. This coevolution of male setae and female elytra has attracted much attention since Darwin. However, there has been little examination of their biomechanical functioning despite increasing knowledge on biofibrillar adhesion. Here, we report and compare, for the first time, the mechanisms of underwater attachment using two hair types, the primitive spatula and derived 'passive' sucker, found in male diving beetles. Results from interspecific scaling of protarsal palettes and adhesion by single seta suggest better performance in the later-evolved circular (sucker) setae. Spatula setae with a modified shallow sucker and channels use the combined mechanisms of suction and viscous resistance for adhesion. Velocity-dependent adhesion provides sufficient control for resisting the female's erratic movements while also detaching easily through slow peeling. Direction-dependent shear resistance helps reorient setae surfaces into a preferred direction for effective adhesion. Seta deformation using different mechanisms for circular and spatula setae reduces the force that is transmitted to the contact interface. A softer spring in spatula setae explains their adhesion at lower preloads and assists in complete substrate contact. Attachment mechanisms revealed in adhesive setae with modified spatula and passive suckers provide insights for bioinspired designs of underwater attachment devices.
雄潜水甲虫利用特化的粘性刚毛在水下求偶时附着在雌甲虫的鞘翅上。自达尔文以来，这种雄性刚毛和雌性鞘翅的协同进化一直引起了广泛关注。然而，尽管人们对生物纤维的粘附有了更多的了解，但对它们的生物力学功能却很少进行研究。在这里，我们首次报道并比较了两种毛类型（原始勺状毛和衍生的“被动”吸盘）在雄性潜水甲虫水下附着中的机制。通过种间跗节垫的比例缩放和单根刚毛的附着结果表明，后来进化的圆形（吸盘）刚毛具有更好的性能。具有改良的浅吸盘和通道的勺状刚毛利用抽吸和粘性阻力的组合机制进行附着。速度依赖的附着提供了足够的控制，以抵抗雌性的不规则运动，同时通过缓慢剥离轻松脱离。方向相关的剪切阻力有助于将刚毛表面重新定向到有效附着的优选方向。圆形和勺状刚毛使用不同机制进行的刚毛变形减少了传递到接触界面的力。勺状刚毛中的较软弹簧解释了它们在较低预载下的附着，并有助于完全接触基底。具有改良勺状和被动吸盘的粘性刚毛的附着机制为水下附着装置的仿生设计提供了启示。
