Complete Mitochondrial Genome and Novel Gene Organization of Ryssota otaheitana
(Pulmonata: Chronidae), and its Implications on the Stylommatophora Phylogeny

Amor M. Damatac II1* and Ian Kendrich C. Fontanilla1,2

1Institute of Biology, University of the Philippines,
Diliman, Quezon City 1101 Philippines
2Philippine Genome Center, University of the Philippines,
Diliman, Quezon City 1101 Philippines,

*Corresponding Author: This email address is being protected from spambots. You need JavaScript enabled to view it.




Whole mitochondrial genomes (mitogenomes) have been increasingly used as markers for phylogenetic inferences. In the Philippines, a marine snail from the Conidae family has been the only species to date whose mitogenome has been fully sequenced, despite the country’s rich malacofaunal diversity particularly in the terrestrial environment. In this study, we sequenced the complete mitogenome of the land snail Ryssota otaheitana (Chronidae), an endemic Philippine pulmonate species. The mitogenome is 13,888 bp in length and encodes the typical 37 genes – including 13 protein-coding, 22 tRNA, and 2 rRNA genes. Short intergenic spacers were found – including a reduced, 42-bp putative control region. Although the gene content is conserved, R. otaheitana showed a novel mitogenome organization involving the translocation of tRNASerine and NADH dehydrogenase subunit 4 gene segment. Combined with available stylommatophoran mitogenomes, different datasets from concatenated sequences of protein-coding and rRNA genes were used for phylogenetic reconstructions. Bayesian Inference (BI) and Maximum Likelihood (ML) trees congruently supported several monophyletic clades within the Stylommatophora such as the Helicoidea, Urocoptoidea, Orthurethra, and Limacoidea sensu lato (syn. ‘limacoid clade’). R. otaheitana is grouped with Deroceras reticulatum in the lower Stylommatophora and forms the monophyletic Limacoidea sensu lato. Both sequence-based phylogeny and gene order comparisons have led us to a hypothesis that Limacoidea sensu lato is at the base of the ‘non-achatinoid’ clade while supporting the division of ‘achatinoid and ‘non-achatinoid’ groups in the Stylommatophora. This study reports the first complete mitogenome from the Chronidae family, which can be used further for the molecular phylogeny of Philippine snails and gastropods at large.



The suborder Stylommatophora comprises the majority of pulmonate gastropods and terrestrial mollusks in the world (Barker 2001). Its higher classification was traditionally based on the excretory system anatomy (Pilsbry 1900); however, groupings at the lower level were unclear due to inconsistent findings from morphological datasets (Shileyko 1979, Nordsieck 1986, Tillier, 1989). Given the challenges of traditional techniques, their lineage reconstructions have later shifted towards the use of molecular characters due to their higher resolving power. Wade et al. (2001) provided the first extensive molecular phylogeny of the Stylommatophora, which showed an unexpected separation into ‘achatinoid’ and ‘non-achatinoid’ groups. Such analyses have increased in the past years primarily due to the extent of molecular data to produce large sets of discrete, heritable, and unambiguous characters that can be effectively used for systematic inferences (Hillis 1987, Grauer and Li 2000). . . . . read more



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