The complete mitogenome of the invasive Japanese mud snail Batillaria attramentaria (Gastropoda: Batillariidae) from Elkhorn Slough, California, USA.

Genomic analysis of the invasive marine snail Batillaria attramentaria from Elkhorn Slough, Moss Landing, California, USA using 150 bp paired-end Illumina sequences resulted in the assembly of its complete mitogenome. The mitogenome is 16,095 bp in length and contains 2 rRNA, 13 protein-coding, and 22 tRNA genes (GenBank Accession MN557850). Gene content and organization of B. attramentaria are identical to the Turritellidae and Pachychilidae. The phylogenetic analysis of B. attramentaria resolves it in a fully supported clade with these same two families in the superfamily Cerithioidea. Nucleotide BLAST searches of the Elkhorn Slough cox1 gene of B. attramentaria yielded identical sequences from invasive populations from California and British Columbia, and native populations from northeastern and central Japan. These data show that mitogenome sequencing is a useful tool for studying the classification and phylogenetic history Cerithioidea.

The Batillaridae are aquatic snails that occur along coastal intertidal and shallow estuarine lagoons. The family contains four genera sensu stricto and 14 species (Ozawa et al. 2009). One of these genera, Batillaria, includes a highly invasive marine snail B. attramentaria (Byers 1999, 2000; Miura et al. 2006). Batillaria was first introduced in March of 1930 into Elkhorn Slough, California, USA in a shipment of 150 boxes of oysters that arrived from Japan (Bonnot 1935). This shipment and perhaps others that followed inadvertently introduced B. attramentaria and more than 50 other invertebrates into the slough (Wasson et al. 2001). The population of B. attramentaria in Elkhorn Slough was estimated at 1 billion, and in California, it was responsible for displacing the native snail Cerithidea californica (Byers 1999). Here, we performed high-throughput sequencing on a specimen of B. attramentaria from Elkhorn Slough to determine its mitogenome structure and phylogenomic relationship to other gastropods in the superfamily Cerithioidea.

DNA was extracted from B. attramentaria (Voucher Specimen-Hartnell College #263) following the protocol of Lindstrom et al. (2011). The 150 bp PE Illumina library construction and sequencing was performed by myGenomics, LLC (Alpharetta, Georgia, USA). The mitogenome was assembled using 22,355,422 reads with the default de novo settings in MEGAHIT (Li et al. 2015). The genes were annotated with NCBI ORFfinder and MITOS (Bernt et al. 2013). Alignment of the B. attramentaria mitogenome to other Gastropoda was completed with MAFFT (Katoh and Standley 2013). The RAxML analysis was run using T-REX (Boc et al. 2012) with the GTR + gamma model and 1000 bootstraps. The tree was visualized with TreeDyn 198.3 at Phylogeny.fr (Dereeper et al. 2008).

The mitogenome of B. attramentaria (GenBank MN557850) is 16,095 bp in length and has a base composition of 30.14% A, 35.24% T, 17.01% G, and 17.61% C. It contains 2 rRNA (rnl, rns), 13 electron transport and oxidative phosphorylation genes, and 22 tRNAs (tRNA-Leu and tRNA-Ser are duplicated). All 13 protein-coding genes initiate with the ATG codon. Most of the genes terminate with the TAA codon, however, cox2, nad1, and nad2 terminate with TAG. The mitogenome of B. attramentaria is identical in gene content and organization to Turritella (Family Turritellidae) and Tylomelania (Pachychilidae) (Hilgers et al. 2016; Zeng et al. 2016). These three families have tandemly arranged tRNA-Arg and tRNA-Gln genes. In other published Cerithioidea mitogenomes, tRNA-Gln is situated on the chromosome with tRNA-Ser, and tRNA-Arg is positioned in between tRNA-Cys and tRNA-Ala. Phylogenetic analysis of B. attramentaria resolves it in a fully supported clade with Turritella and Tylomelania in the superfamily Cerithioidea (Figure 1). Strong et al. (2011) previously reported a similar phylogenetic relationship between the Batillariidae, Turritellidae, and Pachychilidae based on 16S and 28S rRNA DNA sequences. Analysis of the B. attramentaria cox1 sequence found identical sequences from invasive specimens from Elkhorn Slough, California and British Columbia, Canada, and native specimens from northeastern and central Japan (Kojima et al. 2004; Miura et al. 2006; Castelin et al. 2016).

Figure 1.

Maximum-likelihood phylogram of Batillaria attramentaria and related gastropod mitogenomes. Superfamilies are listed to the right. Numbers along branches are bootstrap supports based on 1000 nreps. The legend below represents the scale for nucleotide substitutions.