The genome sequence of the variegated scallop, Mimachlamys varia (Linnaeus, 1758)

Draft genome assembly for the purple-hinged rock scallop (Crassadoma gigantea)

Objectives

This genomic sequence for the purple-hinged rock scallop, Crassadoma gigantea , is a substantial improvement over currently available NCBI genomes for the species and will be an important resource for future genomic research, including ongoing and future population genetic studies. Purple-hinged rock scallops are found along the west coast of North America with a native range from Northern Alaska to Northern Mexico and found to depths of up to ~ 50 m. While not commercially harvested, this species is harvested recreationally and is a candidate of interest for aquaculture and conservation.

Data description

The draft genome for C. gigantea is 817.3 MB, containing 7,183 scaffolds (contig N50 = 287.9 Kb, scaffold N50 = 965.5 Kb). Benchmarking Universal Single-Copy Orthologs (BUSCO) analysis using the 5295 genes in the mollusca_odb10 database had a 93.3% completeness value (92.7% single, 0.6% duplicated). Repeat elements made up 32.23% of the genome. MetaEuk reference-based discovery identified and annotated 23,409 unique protein sequences. Functional annotation was completed by Pannzer2. This assembly will contribute to the ongoing population genetic research on this species.

Haplotype-resolved genomes provide insights into the origins and functional significance of genome diversity in bivalves

Bivalves are famed for exhibiting vast genetic diversity of poorly understood origins and functional significance. Through comparative genomics, we demonstrate that high genetic diversity in these invertebrates is not directly linked to genome size. Using oysters as a representative clade, we show that despite genome size reduction during evolution, these bivalves maintain remarkable genetic variability. By constructing a haplotype-resolved genome for Crassostrea sikamea, we identify widespread haplotype divergent sequences (HDSs), representing genomic regions unique to each haplotype. We show that HDSs are driven by transposable elements, playing a key role in creating and maintaining genetic diversity during oyster evolution. Comparisons of haplotype-resolved genomes across four bivalve orders uncover diverse HDS origins, highlighting a role in genetic innovation and expression regulation across broad timescales. Further analyses show that, in oysters, haplotype polymorphisms drive gene expression variation, which is likely to promote phenotypic plasticity and adaptation. These findings advance our understanding of the relationships among genome structure, diversity, and adaptability in a highly successful invertebrate group.

A genome-based phylogeny for Mollusca is concordant with fossils and morphology

Extreme morphological disparity within Mollusca has long confounded efforts to reconstruct a stable backbone phylogeny for the phylum. Familiar molluscan groups-gastropods, bivalves, and cephalopods-each represent a diverse radiation with myriad morphological, ecological, and behavioral adaptations. The phylum further encompasses many more unfamiliar experiments in animal body-plan evolution. In this work, we reconstructed the phylogeny for living Mollusca on the basis of metazoan BUSCO (Benchmarking Universal Single-Copy Orthologs) genes extracted from 77 (13 new) genomes, including multiple members of all eight classes with two high-quality genome assemblies for monoplacophorans. Our analyses confirm a phylogeny proposed from morphology and show widespread genomic variation. The flexibility of the molluscan genome likely explains both historic challenges with their genomes and their evolutionary success.

Chromosome-level genome assembly of the bay scallop Argopecten irradians

The bay scallop, Argopecten irradians, is a species of major commercial, cultural, and ecological importance. It is endemic to the eastern coast of the United States, but has also been introduced to China, where it supports a significant aquaculture industry. Here, we provide an annotated chromosome-level reference genome assembly for the bay scallop, assembled using PacBio and Hi-C data. The total genome size is 845.9 Mb, distributed over 1,503 scaffolds with a scaffold N50 of 44.3 Mb. The majority (92.9%) of the assembled genome is contained within the 16 largest scaffolds, corresponding to the 16 chromosomes confirmed by Hi-C analysis. The assembly also includes the complete mitochondrial genome. Approximately 36.2% of the genome consists of repetitive elements. The BUSCO analysis showed a completeness of 96.2%. We identified 33,772 protein-coding genes. This genome assembly will be a valuable resource for future research on evolutionary dynamics, adaptive mechanisms, and will support genome-assisted breeding, contributing to the conservation and management of this iconic species in the face of environmental and pathogenic challenges.

Taxonomic Distribution and Molecular Evolution of Mytilectins

R-type lectins are a widespread group of sugar-binding proteins found in nearly all domains of life, characterized by the presence of a carbohydrate-binding domain that adopts a β-trefoil fold. Mytilectins represent a recently described subgroup of β-trefoil lectins, which have been functionally characterized in a few mussel species (Mollusca, Bivalvia) and display attractive properties, which may fuel the development of artificial lectins with different biotechnological applications. The detection of different paralogous genes in mussels, together with the description of orthologous sequences in brachiopods, supports the formal description of mytilectins as a gene family. However, to date, an investigation of the taxonomic distribution of these lectins and their molecular diversification and evolution was still lacking. Here, we provide a comprehensive overview of the evolutionary history of mytilectins, revealing an ancient monophyletic evolutionary origin and a very broad but highly discontinuous taxonomic distribution, ranging from heteroscleromorphan sponges to ophiuroid and crinoid echinoderms. Moreover, the overwhelming majority of mytilectins display a chimera-like architecture, which combines the β-trefoil carbohydrate recognition domain with a C-terminal pore-forming domain, suggesting that the simpler structure of most functionally characterized mytilectins derives from a secondary domain loss.