Testing Efficacy of Assembly-Free and Alignment-Free Methods for Species Identification Using Genome Skims, with Patellogastropoda as a Test Case.

Most recently, species identification has leaped from DNA barcoding into shotgun sequencing-based "genome skimming" alternatives. Genome skims have mainly been used to assemble organelle genomes, which discards much of the nuclear genome. Recently, an alternative approach was proposed for sample identification, using unassembled genome skims, which can effectively improve phylogenetic signal and identification resolution. Studies have shown that the software Skmer and APPLES work well at estimating genomic distance and performing phylogenetic placement in birds and insects using low-coverage genome skims. In this study, we use Skmer and APPLES based on genome skims of 11 patellogastropods to perform assembly-free and alignment-free species identification and phylogenetic placement. Whether or not data corresponding to query species are present in the reference database, Skmer selects the best matching or closest species with COI barcodes under different sizes of genome skims except lacking species belonging to the same family as a query. APPLES cannot place patellogastropods in the correct phylogenetic position when the reference database is sparse. Our study represents the first attempt at assembly-free and alignment-free species identification of marine mollusks using genome skims, demonstrating its feasibility for patellogastropod species identification and flanking the necessity of establishing a database to share genome skims.