Division of Invertebrate Zoology and Sackler Institute for Comparative Genomics, American Museum of Natural History, New York, NY, USA.
Department of Biology, Washington and Lee University, Lexington, VA, USA.
BMC Ecol Evol. 2022 Jul 9;22(1):89. doi: 10.1186/s12862-022-02042-5.
Spiders have evolved two types of sticky capture threads: one with wet adhesive spun by ecribellate orb-weavers and another with dry adhesive spun by cribellate spiders. The evolutionary history of cribellate capture threads is especially poorly understood. Here, we use genomic approaches to catalog the spider-specific silk gene family (spidroins) for the cribellate orb-weaver Uloborus diversus.
We show that the cribellar spidroin, which forms the puffy fibrils of cribellate threads, has three distinct repeat units, one of which is conserved across cribellate taxa separated by ~ 250 Mya. We also propose candidates for a new silk type, paracribellar spidroins, which connect the puffy fibrils to pseudoflagelliform support lines. Moreover, we describe the complete repeat architecture for the pseudoflagelliform spidroin (Pflag), which contributes to extensibility of pseudoflagelliform axial fibers.
Our finding that Pflag is closely related to Flag, supports homology of the support lines of cribellate and ecribellate capture threads. It further suggests an evolutionary phase following gene duplication, in which both Flag and Pflag were incorporated into the axial lines, with subsequent loss of Flag in uloborids, and increase in expression of Flag in ecribellate orb-weavers, explaining the distinct mechanical properties of the axial lines of these two groups.
蜘蛛进化出了两种粘性捕捉线：一种是由无纺丝器织圆蛛吐出的湿粘性线，另一种是由有纺丝器蜘蛛吐出的干粘性线。有纺丝器捕捉线的进化历史尤其不为人知。在这里，我们使用基因组方法对有纺丝器圆蛛 Uloborus diversus 的蜘蛛特异性丝基因家族（丝氨酸）进行编目。
我们表明，形成有纺丝器线蓬松纤维的有纺丝器丝氨酸由三个不同的重复单元组成，其中一个在相隔约 2.5 亿年的有纺丝器分类群中是保守的。我们还提出了一种新的丝类型的候选者，即副有纺丝器丝氨酸，它将蓬松纤维连接到假鞭毛状支撑线。此外，我们描述了假鞭毛状丝氨酸（Pflag）的完整重复结构，它有助于假鞭毛状轴纤维的伸展性。
我们发现 Pflag 与 Flag 密切相关，支持了有纺丝器和无纺丝器捕捉线的支撑线的同源性。它进一步表明，在基因复制之后，出现了一个进化阶段，其中 Flag 和 Pflag 都被纳入了轴纤维中，随后在 Uloborids 中失去了 Flag，而在无纺丝器织圆蛛中 Flag 的表达增加，解释了这两组轴纤维的独特机械性能。
