Blackledge Todd A, Coddington Jonathan A, Agnarsson Ingi
Department of Biology and Integrated Bioscience Program, University of Akron, Akron, OH, USA.
Commun Integr Biol. 2009 Nov;2(6):459-63. doi: 10.4161/cib.2.6.8855.
Identifying the mechanisms driving adaptive radiations is key to explaining the diversity of life. The extreme reliance of spiders upon silk for survival provides an exceptional system in which to link patterns of diversification to adaptive changes in silk use. Most of the world's 41,000 species of spiders belong to two apical lineages of spiders that exhibit quite different silk ecologies, distinct from their ancestors. Orb spiders spin highly stereotyped webs that are suspended in air and utilize a chemical glue to make them adhesive. RTA clade spiders mostly abandoned silk capture webs altogether. We recently proposed that these two clades present very different evolutionary routes of achieving the same key innovation-escape from the constraints imposed by spinning webs that contain a relatively costly type of physically adhesive cribellate silk. Here, we test the prediction that orb and RTA clade spiders are not only more diverse, but also have higher fecundity than other spiders. We show that RTA clade spiders average 23% higher fecundity and orb spiders average 123% higher fecundity than their ancestors. This supports a functional link between the adaptive escape from cribellate silk and increased resource allocation to reproduction in spiders.
识别驱动适应性辐射的机制是解释生命多样性的关键。蜘蛛对蛛丝的极端依赖为将多样化模式与蛛丝使用的适应性变化联系起来提供了一个特殊的系统。世界上41000种蜘蛛中的大多数属于蜘蛛的两个顶端谱系，它们表现出截然不同的蛛丝生态，与它们的祖先不同。圆蛛编织高度定型的网，这些网悬挂在空气中，并利用一种化学胶水使其具有粘性。RTA进化枝蜘蛛大多完全放弃了用蛛丝捕捉猎物的网。我们最近提出，这两个进化枝呈现出非常不同的进化路径，却实现了相同的关键创新——摆脱由含有相对昂贵的物理粘性筛器蛛丝的网所带来的限制。在这里，我们检验了一个预测，即圆蛛和RTA进化枝蜘蛛不仅比其他蜘蛛种类更多样化，而且繁殖力更高。我们发现，RTA进化枝蜘蛛的平均繁殖力比其祖先高23%，圆蛛的平均繁殖力比其祖先高123%。这支持了蜘蛛从筛器蛛丝的适应性逃脱与增加繁殖资源分配之间的功能联系。
