Table_3_Diversification of spider silk properties in an adaptive radiation of Hawaiian orb-weaving spiders.xlsx

IntroductionThe design of biological structures and the materials composing those structures are intimately connected to performance in biological systems. Spider webs present an excellent example of how design and materials interact during their function in capturing prey. Major shifts in how spider webs capture prey have occurred due to evolutionary changes in both web architecture and silk properties. However, these shifts are mostly described for long timescales deep within the spider’s tree of life. Hawaiian Tetragnatha presents an opportunity to ask if such shifts can occur at much shorter timescales because web design diverges significantly among closely related species on the same island while also converging with more distant relatives on other islands. Here, we provide an initial test of whether or not silk properties diversified during the recent adaptive radiation of Hawaiian Tetragnatha.
MethodsWe obtained radial and capture spiral silk from orb webs for spiders on two islands and tested their tensile and adhesive properties. We also used solution-state NMR to compare the composition of low molecular weight compounds in the glue because of their influence on capture spiral stickiness.
ResultsResults showed differences in the stiffness of radial silk among four populations of Hawaiian Tetragnatha, while extensibility remained unchanged. Although not statistically different, radial strength and toughness varied twofold among species. Stickiness varied threefold among the four populations of orb weavers. No conspicuous qualitative differences in the low molecular weight compound composition of aggregate glue were found, suggesting that differences in capture spiral stickiness were due to the amount or arrangement of glue droplets on threads.
DiscussionWhile our sampling is modest, our data provide the first evidence that silk properties can evolve measurably over the relatively short timescales of the adaptive radiation of Hawaiian Tetragnatha spiders.

引言
生物结构的设计及其组成材料，与生物系统的功能表现紧密相关。蜘蛛网便是绝佳范例，展现了其结构设计与材料特性在捕猎功能中如何协同作用。蜘蛛捕猎蛛网的运作方式曾发生过重大转变，这源于蛛网结构和蛛丝特性的共同演化改变。然而，这类转变的相关研究大多聚焦于蜘蛛演化树深处的长期时间尺度。夏威夷肖蛸属（Hawaiian Tetragnatha）为我们提供了绝佳的研究契机，用以探究这类转变是否可在更短的时间尺度内发生：同一岛屿上的近缘物种间蛛网设计差异显著，而它们又与其他岛屿上的远缘类群呈现出结构趋同的特征。本研究首次检验了夏威夷肖蛸属在近期适应性辐射过程中，蛛丝特性是否发生了分化。

研究方法
我们从两座岛屿上的圆网蛛圆网中采集了放射状蛛丝与捕捉螺旋丝，并测试其拉伸与黏附性能。此外，我们利用溶液态核磁共振（solution-state NMR）技术，比较了蛛胶中低分子量化合物的组成——这类化合物会对捕捉螺旋丝的黏性产生显著影响。

研究结果
结果显示，四个夏威夷肖蛸属种群的放射状蛛丝刚度存在显著差异，而延展性未发生改变。尽管未达到统计学显著性差异，但不同物种的放射状蛛丝强度与韧性差异可达两倍。四种圆网蛛种群的黏性差异可达三倍。聚集状蛛胶的低分子量化合物组成未出现明显的定性差异，这表明捕捉螺旋丝的黏性差异源于蛛胶液滴在蛛丝上的含量或排布方式。

讨论
尽管本次研究的采样规模有限，但我们的数据首次证实，夏威夷肖蛸属蜘蛛在适应性辐射的相对较短时间尺度内，蛛丝特性可发生可检测的演化改变。