De Novo Genome Assembly Highlights the Role of Lineage-Specific Gene Duplications in the Evolution of Venom in Fea's Viper (Azemiops feae)

Abstract

Despite the medical significance to humans and important ecological roles filled by vipers, few high-quality genomic resources exist for these snakes outside of a fewgenera of pitvipers. Herewe sequence, assemble, and annotate the genome of Fea's Viper (Azemiops feae). This taxon is distributed in East Asia and belongs to a monotypic subfamily, sister to the pitvipers. The newly sequenced genome resulted in a 1.56 Gb assembly, a contig N50 of 1.59 Mb, with 97.6%of the genome assembly in contigs .50 Kb, and a BUSCOcompleteness of 92.4%.We found that A. feae venomis primarily composed of phospholipase A2 (PLA2) proteins expressed by genes that likely arose from lineage-specific PLA2 gene duplications. Additionally, we show that renin, an enzyme associated with blood pressure regulation in mammals and known from the venoms of two viper species including A. feae, is expressed in the venomgland at comparative levels to known toxins and is present in the venomproteome. The cooption of this gene as a toxinmay bemorewidespread in viperids than currently known. To investigate the historical population demographics of A. feae, we performed coalescent-based analyses and determined that the effective population size has remained stable over the last 100 kyr. This suggests Quaternary glacial cycles likely had minimal influence on the demographic history of A. feae. This newly assembled genome will be an important resource for studying the genomic basis of phenotypic evolution and understanding the diversification of venom toxin gene families.