Opell Brent D, Burba Cassandra M, Deva Pritesh D, Kin Matthew H Y, Rivas Malik X, Elmore Hannah Mae, Hendricks Mary L
Department of Biological Sciences Virginia Tech Blacksburg VA USA.
Ecol Evol. 2019 Aug 15;9(17):9841-9854. doi: 10.1002/ece3.5525. eCollection 2019 Sep.
An orb web's adhesive capture spiral is responsible for prey retention. This thread is formed of regularly spaced glue droplets supported by two flagelliform axial lines. Each glue droplet features a glycoprotein adhesive core covered by a hygroscopic aqueous layer, which also covers axial lines between the droplets, making the entire thread responsive to environmental humidity.We characterized the effect of relative humidity (RH) on ability of and thread arrays to retain houseflies and characterize the effect of humidity on their droplet properties. Using these data and those of from a previous study, we then develop a regression model that correlated glycoprotein and flagelliform fiber properties with prey retention time. The model selection process included newly determined, humidity-specific Young's modulus and toughness values for the three species' glycoproteins.Argiope droplets are more hygroscopic than droplets, causing the glycoprotein within droplets to become oversaturated at RH greater than 55% RH and their extension to decrease, whereas droplet performance increases to 72% RH. This difference is reflected in species' prey retention times, with that of peaking at 55% RH and that of at 72% RH.Fly retention time was explained by a regression model of five variables: glue droplet distribution, flagelliform fiber work of extension, glycoprotein volume, glycoprotein thickness, and glycoprotein Young's modulus.The material properties of both glycoprotein and flagelliform fibers appear to be phylogenetically constrained, whereas natural selection can more freely act on the amount of each material invested in a thread and on components of the thread's aqueous layer. Thus, it becomes easier to understand how natural selection can tune the performance of viscous capture threads by directing small changes in these components.
圆网蛛的粘性捕获螺旋负责捕获猎物。该蛛丝由规则排列的胶滴构成，由两条鞭毛状轴线支撑。每个胶滴都有一个糖蛋白粘性核心，被一层吸湿水层覆盖，该水层也覆盖了胶滴之间的轴线，使整个蛛丝对环境湿度有反应。我们表征了相对湿度（RH）对蜘蛛丝阵列捕获家蝇能力的影响，并表征了湿度对其胶滴特性的影响。利用这些数据以及之前一项研究的数据，我们开发了一个回归模型，将糖蛋白和鞭毛状纤维特性与猎物保留时间相关联。模型选择过程包括新测定的三种蜘蛛糖蛋白在特定湿度下的杨氏模量和韧性值。横纹金蛛的胶滴比大腹园蛛的胶滴更具吸湿性，导致横纹金蛛胶滴内的糖蛋白在相对湿度大于55%时变得过饱和，其延伸性降低，而大腹园蛛胶滴的性能在相对湿度达到72%时仍会增加。这种差异反映在不同蜘蛛捕获猎物的时间上，横纹金蛛的捕获时间在相对湿度55%时达到峰值，大腹园蛛的捕获时间在相对湿度72%时达到峰值。苍蝇的保留时间由一个包含五个变量的回归模型解释：胶滴分布、鞭毛状纤维的拉伸功、糖蛋白体积、糖蛋白厚度和糖蛋白杨氏模量。糖蛋白和鞭毛状纤维的材料特性似乎在系统发育上受到限制，而自然选择可以更自由地作用于投入到蛛丝中的每种材料的数量以及蛛丝水层的成分。因此，就更容易理解自然选择如何通过引导这些成分的微小变化来调节粘性捕获蛛丝的性能。
