Supersaturation with water explains the unusual adhesion of aggregate glue in the webs of the moth-specialist spider, Cyrtarachne akirai
Supersaturation with water explains the unusual adhesion of aggregate glue in the webs of the moth-specialist spider, Cyrtarachne akirai
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DOI：
10.1098/rsos.181296
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发表时间：
2018-11-01
影响因子：
3.5
通讯作者：
Blackledge, Todd A.
中科院分区：
文献类型：
--
作者：
Diaz, Candido;Tanikawa, Akio;Blackledge, Todd A.
蛛形纲蜘蛛所结的圆球网依靠粘在一起的捕丝来留住猎物。飞蛾是大多数蜘蛛的猎物，因为它们的鳞片会脱落并污染胶滴，大大降低粘结力。Cyrtarachne是飞蛾专家，它的捕丝能很好地附着在飞蛾上。我们比较了Cyrtarachne骨料胶与其他织球蜘蛛的粘合性能和化学性质，以测试有关其结构、化学和性能的假设，这些假设可以解释Cyrtarachne胶的强度。我们发现，Cyrtarachne捕获线上异常大的胶滴使其在玻璃基板上的粘附性比典型球织物种捕获线高出约8倍，但按胶量归一化后，Cyrtarachne的粘附性与其他物种相似。黏度随大气湿度的变化可发生1000倍以上的可逆变化，在黏度约为10(5)-10(6)cst时，许多种类的球蛛黏附强度最大，扩散和体黏聚的贡献最优。相比之下，在最大黏合剂湿度下，Cyrtarachne骨料胶滴的粘度约低1000倍，可能有助于飞蛾在鳞片上快速扩散。胶滴的吸水部分是由吸湿性低分子量化合物控制的。核磁共振结果表明，该胶含有多种未知的低分子量化合物。这些化合物可能有助于解释Cyrtarachne如何产生如此大而低粘度的胶滴，以及为什么这些胶滴在短暂老化或暴露于甚至轻微干燥（例如< 80% RH）的条件后迅速失去水体积，从而永久降低其粘附性。我们推测，大胶滴尺寸和低粘度的结合有助于cytarachne胶穿透飞蛾鳞片之间的间隙。
Orb webs produced by araneoid spiders depend upon aggregate glue-coated capture threads to retain their prey. Moths are challenging prey for most spiders because their scales detach and contaminate the glue droplets, significantly decreasing adhesion. Cyrtarachne are moth-specialist orb-weaving spiders whose capture threads adhere well to moths. We compare the adhesive properties and chemistry of Cyrtarachne aggregate glue to other orb-weaving spiders to test hypotheses about their structure, chemistry and performance that could explain the strength of Cyrtarachne glue. We show that the unusually large glue droplets on Cyrtarachne capture threads make them approximately 8 times more adhesive on glass substrate than capture threads from typical orb-weaving species, but Cyrtarachne adhesion is similar to that of other species after normalization by glue volume. Glue viscosity reversibly changes over 1000-fold in response to atmospheric humidity, and the adhesive strength of many species of orb spiders is maximized at a viscosity of approximately 10(5)-10(6) cst where the contributions of spreading and bulk cohesion are optimized. By contrast, viscosity of Cyrtarachne aggregate glue droplets is approximately 1000 times lower at maximum adhesive humidity, likely facilitating rapid spreading across moth scales. Water uptake by glue droplets is controlled, in part, by hygroscopic low molecular weight compounds. NMR showed evidence that Cyrtarachne glue contains a variety of unknown low molecular weight compounds. These compounds may help explain how Cyrtarachne produces such exceptionally large and low viscosity glue droplets, and also why these glue droplets rapidly lose water volume after brief ageing or exposure to even slightly dry (e.g. < 80% RH) conditions, permanently reducing their adhesion. We hypothesize that the combination of large glue droplet size and low viscosity helps Cyrtarachne glue to penetrate the gaps between moth scales.