The evolutionary history of cribellate orb-weaver capture thread spidroins

Abstract

Background 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. Results 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. Conclusions 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.

Chromosome-level genome and the identification of sex chromosomes in Uloborus diversus

“…S1 ). This differs somewhat from the results reported by Correa-Garhwal et al [ 43 ], which identified 10 tandem repeats. As with previous reports on the structure of AcSp [ 26 , 108–110 ], we also found that the repeats are remarkably well homogenized.…”

“…We found 12 full-length candidate sequences, including at least 1 candidate for each of the 7 types of spidroin used by cribellate orb-weavers, as well as candidate sequences for the ampullate spidroin (AmSp) and 2 proposed paracribellar spidroins (Sp_vA and Sp_vB) recently reported by Correa-Garhwal et al [ 43 ]. There were no gaps in the assembly interrupting our candidate spidroin sequences with the exception of Sp_vA.…”

“…While most single-exon genes tend to be small highly expressed proteins such as histones, spidroins are a rare exception. The single-exon structure of spidroin genes has been noted in other species, as well as most recently in U. diversus [ 26 , 43, 99–106 ].…”

“…Of the 22 genomes, only 7 represent the Araneoidea [ 28 , 29 , 32 , 39 ] or ecribellate orb-weavers, 2 of which have been assembled to chromosome scale [ 29 , 32 ]. While Correa-Garhwal et al [ 43 ] recently published a scaffold-scale 10× assembly of the Uloborus diversus genome, we provide the first chromosome-scale assembly for a member of the UDOH clade. In addition, to date, only 1 genome represents a member of the cribellate retrolateral tibial apophysis (RTA) clade, which is the sister clade to the UDOH clade (Fig.…”

Rapid molecular diversification and homogenization of clustered major ampullate silk genes in Argiope garden spiders

“…pilipes and T . clavipes [ 51 ] and is present in some MaSp repeat sequence of Uloborus diversus , a distantly related cribellate orb-weaver [ 128 ]. Given its prominence in Argiope and widespread taxonomic distribution, GQQGPG may represent a central functional motif whose expansion is tied to changes in initial fiber crystallinity and disorder.…”