Molecular evolution of venom proteins in Ctenidae (Order: Araneae) spiders

Abstract

Spiders comprise the largest group of venomous animals and are a pivotal component of the global ecosystem with approximately 50,000 species spread across nearly every habitat on Earth. The family Ctenidae Keyserling, 1877 comprises small to large nocturnal wandering spiders. There are drastic differences in the venom potency amongst wandering spiders. The bite of the highly aggressive Brazilian wandering spider (Phoneutria nigriventer) causes pain, cramps, priapism, and arrhythmia, whereas the bite of ctenids dwelling in the temperate forests of North America have no recorded adverse symptoms. Inhibitor Cystine Knot toxins (ICKs) make up the majority of the venom composition across the spider tree of life and exist as complex multi-copy gene families in which one species may express up to 100 homologs. To develop an understanding of venom evolution in wandering spiders, we reconstructed a species-level phylogeny using transcriptomic sequences and conducted feeding experiments to evaluate the variation in venom biology of ctenid spiders in the U.S. We found that U.S. ctenids do not represent a single lineage, and that venom utilization strategies differed within the family. To characterize the patterns of molecular evolution of ICK toxins in wandering spiders. To do this, we used venom gland transcriptomics and proteomics to identify and characterize the molecular evolution of 626 unique coding sequences of ICK peptides. No amino acid sites were found to have evidence of pervasive positive selection, though 12 out of 80 sites contained a portion of branches within the gene family phylogeny with evidence of episodic positive selection.The final objective was to compare the genomic architecture and patterns of duplication in spiders with publicly available genome sequences. We demonstrated that the current state of spider genome assemblies presents limitations in the analyses that can be performed We were not able to identify many ICKs in the assemblies of all species but were able to construct a phylogeny of ICKs present as duplicates in three species. Through this investigation, we revealed that ICKs have undergone duplication events before and after speciation events, indicating these events have occurred throughout the evolutionary history of spiders.