The mitochondrial genome of Pomacea maculata (Gastropoda: Ampullariidae)

Comparative Mitogenome Analysis of Two Native Apple Snail Species (Ampullariidae, Pomacea) from Peruvian Amazon

Apple snails of the genus Pomacea Perry, 1810 (Mollusca: Caenogastropoda: Ampullariidae) are native to the Neotropics and exhibit high species diversity, holding cultural and ecological significance as an important protein source in Peru. However, most genetic studies in Pomacea have focused mostly on invasive species, especially in Southeast Asia, where they are considered important pests. In this study, we assembled and annotated the mitochondrial genomes of two Pomacea species native to the Peruvian Amazon: Pomacea reevei Ampuero & Ramírez, 2023 and Pomacea aulanieri (Deville & Hupé, 1850). The mitogenomes of P. reevei and P. aulanieri comprise 15,660 and 16,096 bp, respectively, and contain the typical 37 genes of the animal mitochondria with a large control region of 292 bp in P. reevei and 524 bp in P. aulanieri-which fall within the range of what is currently known in Pomacea. Comparisons with previously published mitogenomes in Pomacea revealed differences in the overlapping of adjacent genes, the size of certain protein-coding genes (PCGs) and the secondary structure of some tRNAs that are consistent with the phylogenetic relationships between these species. These findings provide valuable insights into the systematics and genomics of the genus Pomacea.

Comparative Characterization of the Complete Mitochondrial Genomes of the Three Apple Snails (Gastropoda: Ampullariidae) and the Phylogenetic Analyses

The apple snails Pomacea canaliculata, Pomacea diffusa and Pomacea maculate (Gastropoda: Caenogastropoda: Ampullariidae) are invasive pests causing massive economic losses and ecological damage. We sequenced and characterized the complete mitochondrial genomes of these snails to conduct phylogenetic analyses based on comparisons with the mitochondrial protein coding sequences of 47 Caenogastropoda species. The gene arrangements, distribution and content were canonically identical and consistent with typical Mollusca except for the tRNA-Gln absent in P. diffusa. An identifiable control region (d-loop) was absent. Bayesian phylogenetic analysis indicated that all the Ampullariidae species clustered on the same branch. The genus Pomacea clustered together and then with the genus Marisa. The orders Architaenioglossa and Sorbeoconcha clustered together and then with the order Hypsogastropoda. Furthermore, the intergenic and interspecific taxonomic positions were defined. Unexpectedly, Ceraesignum maximum, Dendropoma gregarium, Eualetes tulipa and Thylacodes squamigerus, traditionally classified in order Hypsogastropoda, were isolated from the order Hypsogastropoda in the most external branch of the Bayesian inference tree. The divergence times of the Caenogastropoda indicated that their evolutionary process covered four geological epochs that included the Quaternary, Neogene, Paleogene and Cretaceous periods. This study will facilitate further investigation of species identification to aid in the implementation of effective management and control strategies of these invasive species.

Comparative mitogenome analysis on species of four apple snails (Ampullariidae: Pomacea)

The genus Pomacea contains most of the economically important Ampullariid apple snails. Five Pomacea species were reported introduced out of their native ranges, including three highly invasive species, i.e. P. maculata, P. canaliculata and an unidentified species, Pomacea sp. In this study, the mitogenome of P. maculata was determined, which carried typical gene set of metazoan mitogenomes and shared the same gene rearrangement of Ampullariidae mitogenomes. The control region of the P. maculata has a 13-bp inverted repeat unit. We compared the mitogenome of P. maculata with P. canaliculata, Pomacea sp. and the aquatic pet species, P. diffusa. The three highly invasive species showed high sequence similarity of PCGs and RNAs. atp8 and nad2 showed the lowest similarity and the highest Ka/Ks ratios, indicating that both genes have potential for studying species identification and populations genetics in apple snails. All PCGs have the Ka/Ks ratios <1, indicating the existence of purifying selection in Pomacea species. We reconstructed phylogenetic trees using 14 Caenogastropda species based on sequences of PCGs and rRNAs using Bayesian inference. Pomacea maculata grouped with other Ampullariids and was most closely related to Pomacea sp. The mitogenome of P. maculata provides useful genetic resource for exploring the genetics and evolution of P. maculata and other apple snails.

The complete mitochondrial genome of Pomacea diffusa (Gastropoda: Ampullariidae)

In this study, we analyzed the complete mitochondrial genome of the spike-topped apple snail, Pomacea diffusa Blume, 1957 (Gastropoda: Ampullariidae). The mitochondrial genome of P. diffusa was 16,373 bp, consisting 13 protein-coding genes, 2 rRNAs, and 22 tRNAs and a non-coding region with a 12 bp repeat unit. There were 29 mitochondrial genes of P. diffusa are distributed on the H-strand, and the other eight tRNA genes encoded on the L-strand. The average AT content of 13 protein-coding genes was 68.7%. A phylogenetic analysis showed that there was a close relationship between P. diffusa and invasive apple snail species, Pomacea canaliculata and Pomacea aff. maculata.

Sequencing of the complete mitochondrial genomes of eight freshwater snail species exposes pervasive paraphyly within the Viviparidae family (Caenogastropoda)

Phylogenetic relationships among snails (Caenogastropoda) are still unresolved, and many taxonomic categories remain non-monophyletic. Paraphyly has been reported within a large family of freshwater snails, Viviparidae, where the taxonomic status of several species remains questionable. As many endemic Chinese viviparid species have become endangered during the last few decades, this presents a major obstacle for conservation efforts. Mitochondrial genomes (mitogenomes) carry a large amount of data, so they can often provide a much higher resolution for phylogenetic analyses in comparison to the traditionally used molecular markers. To help resolve their phylogenetic relationships, the complete mitogenomes of eight Chinese viviparid snails, Viviparus chui, Cipangopaludina chinensis, C. ussuriensis, C. dianchiensis (endangered), Margarya melanioides (endangered), M. monodi (critically endangered), Bellamya quadrata and B. aeruginosa, were sequenced and compared to almost all of the available caenogastropod mitogenomes. Viviparidae possess the largest mitogenomes (16 392 to 18 544 bp), exhibit the highest A+T bias (72.5% on average), and some exhibit unique gene orders (a rearrangement of the standard MYCWQGE box), among the Caenogastropoda. Apart from the Vermetidae family and Cerithioidea superfamily, which possessed unique gene orders, the remaining studied caenogastropod mitogenomes exhibited highly conserved gene order, with minimal variations. Maximum likelihood and Bayesian inference analyses, used to reconstruct the phylogenetic relationships among 49 almost complete (all 37 genes) caenogastropod mitogenomes, produced almost identical tree topologies. Viviparidae were divided into three clades: a) Margarya and Cipangopaludina (except C. ussuriensis), b) Bellamya and C. ussuriensis, c) Viviparus chui. Our results present evidence that some Cipangopaludina species (dianchiensis and cathayensis) should be renamed into the senior genus Margarya. The phylogenetic resolution obtained in this study is insufficient to fully resolve the relationships within the 'b' clade, but if C. chinensis proves to be a valid representative of the genus, C. ussuriensis may have to be reassigned a different genus (possibly Bellamya, or even a new genus). Non-monophyly also remains pervasive among the higher (above the family-level) Caenogastropod taxonomic classes. Gene order distance matrix produced a different phylogenetic signal from the nucleotide sequences, which indicates a limited usability of this approach for inferring caenogastropod phylogenies. As phenotypic homoplasy appears to be widespread among some viviparid genera, in order to effectively protect the rapidly diminishing endemic Viviparid populations in China, further detailed molecular phylogenetic studies are urgently needed to resolve the taxonomic status of several species.