Stark Alyssa Y, Yanoviak Stephen P
Department of Biology, University of Louisville, 139 Life Sciences Building, Louisville, KY 40292, USA.
Smithsonian Tropical Research Institute, Balboa, Republic of Panama.
R Soc Open Sci. 2018 Nov 14;5(11):181540. doi: 10.1098/rsos.181540. eCollection 2018 Nov.
In the tropical forest canopy, wingless worker ants must cling to and run along diverse vegetative surfaces with little protection from sun, wind and rain. Ants rely in part on their tiny adhesive tarsal pads to maintain sufficient contact with substrates to prevent falls under these varied conditions. Here, we examined the effects of substrate wettability and surface water on the tarsal pad adhesive performance of a common tropical arboreal ant. Ant adhesion was consistently higher on an intermediately wetting substrate (static water contact angle 90°) when resisting both perpendicular (normal) force and parallel (shear) force. Normal adhesion was maintained on intermediately wetting and hydrophobic substrates following the addition of rain-mimicking water droplets, whereas shear adhesion declined on all substrate types tested after wetting. Ant running speed was slower on wet substrates. On wood substrates, normal and shear adhesion declined with increasing wetness from dry, to misted, to water-soaked. These differences probably contributed to lower ant running speed on wet wood. The results of this study provide the first quantitative assessment of tropical arboreal ant adhesive performance under substrate conditions that are commonly encountered in the rainforest canopy.
在热带森林冠层中，无翅工蚁必须紧贴并沿着各种植物表面爬行，几乎没有防晒、防风和防雨保护。蚂蚁部分依靠其微小的粘性跗垫与基质保持足够接触，以防止在这些多变条件下掉落。在此，我们研究了基质润湿性和表面水对一种常见热带树栖蚂蚁跗垫粘附性能的影响。在抵抗垂直（法向）力和平行（剪切）力时，蚂蚁在中等润湿性基质（静态水接触角90°）上的粘附力始终更高。添加模拟雨滴的水滴后，中等润湿性和疏水性基质上的法向粘附力得以保持，而所有测试基质类型在湿润后剪切粘附力均下降。蚂蚁在湿润基质上的奔跑速度较慢。在木质基质上，从干燥到有薄雾再到被水浸透，随着湿度增加，法向和剪切粘附力均下降。这些差异可能导致蚂蚁在湿润木材上的奔跑速度降低。本研究结果首次对热带雨林冠层常见基质条件下热带树栖蚂蚁的粘附性能进行了定量评估。
