A PacBio Hi-Fi Genome Assembly of the Painter's Mussel Unio pictorum (Linnaeus, 1758)

Abstract

The highly diverse group of freshwater mussels from order Unionida is found in the world's freshwater systems due to several fascinating evolutionary adaptations, including "parental care," and most notably, an obligatory parasitic phase in their early life cycle, called glochidia, which infests and uses fish for nutrition and dispersal. Freshwater mussels play essential ecological roles in freshwater habitats, including water filtration, sediment bioturbation, and nutrient cycling. However, these species are also highly threatened, being one of the faunal groups with the highest recorded extinction rate in the wild. Genomics methods have an incredible potential to promote biodiversity conservation, allowing the characterization of population health, identification of adaptive genetic elements, delineation of conservation units, and providing a framework for predictive assessments of the impact of anthropogenic threats and climate change. Unfortunately, only six freshwater mussel species have had their whole genomes sequenced to date, and only two of these are European species. Here, we present the first genome assembly of the Painter's Mussel, Unio pictorum (Linnaeus, 1758), the type species representative of the order and the most widespread species of the genus in Europe. We used long-read PacBio Hi-Fi sequencing reads to produce a highly contiguous assembly that will pave the way for the study of European freshwater mussels in the Genome Era.

Keywords: PacBio Hi-Fi; Unionida; freshwater mussels; genome assembly.

Fig. 1

A) The map of the potential distribution of Unio pictorum generated by overlapping the points of recent presence records (obtained from 13) with level 5 polygons of the Hydrobasinslayer. On the top left is shown the U. pictorum specimen used for the WGA. B) Left: GenomeScope2 k-mer (21) distribution displaying the estimated genome size (len), homozygosity (aa), heterozygosity (ab), mean k-mer coverage for heterozygous bases (kcov), read error rate (err), the average rate of read duplications (dup), k-mer size used in the run (k:), and ploidy (p:). Right: Assessment of the U. pictorum genome assembly using the KAT comp tool to compare the PacBio Hi-Fi k-mer content within the genome assembly after running purge_dups. Different colors represent the read k-mer frequency in the assembly.