Abstract
Complete mitochondrial (mt) genomes and the gene rearrangements are increasingly used as molecular markers for investigating phylogenetic relationships. Contributing to the complete mt genomes of Gastropoda, especially Pulmonata, we determined the mt genome of the freshwater snail Galba pervia, which is an important intermediate host for Fasciola spp. in China. The complete mt genome of G. pervia is 13,768 bp in length. Its genome is circular, and consists of 37 genes, including 13 genes for proteins, 2 genes for rRNA, 22 genes for tRNA. The mt gene order of G. pervia showed novel arrangement (tRNA-His, tRNA-Gly and tRNA-Tyr change positions and directions) when compared with mt genomes of Pulmonata species sequenced to date, indicating divergence among different species within the Pulmonata. A total of 3655 amino acids were deduced to encode 13 protein genes. The most frequently used amino acid is Leu (15.05%), followed by Phe (11.24%), Ser (10.76%) and IIe (8.346%). Phylogenetic analyses using the concatenated amino acid sequences of the 13 protein-coding genes, with three different computational algorithms (maximum parsimony, maximum likelihood and Bayesian analysis), all revealed that the families Lymnaeidae and Planorbidae are closely related two snail families, consistent with previous classifications based on morphological and molecular studies. The complete mt genome sequence of G. pervia showed a novel gene arrangement and it represents the first sequenced high quality mt genome of the family Lymnaeidae. These novel mtDNA data provide additional genetic markers for studying the epidemiology, population genetics and phylogeographics of freshwater snails, as well as for understanding interplay between the intermediate snail hosts and the intra-mollusca stages of Fasciola spp..
Highlights
Many snails within the families Lymnaeidae and Planorbidae act as intermediate hosts of medically and veterinary important digenean trematodes that infect humans and domestic animals [1,2]
Fascioliasis caused by Fasciola spp. is a signifancant disease of livestock animals causing substantial economic impact [4,5,6,7]
Mitochondrial DNA has long been extensively used as genetic markers to resolve evolutionary relationships among animal species due to their maternal inheritance, higher mutation rates than nuclear genes, and relatively conserved genome structures compared to ribosomal DNA [10,11,12,13,14,15]
Summary
Many snails within the families Lymnaeidae and Planorbidae act as intermediate hosts of medically and veterinary important digenean trematodes that infect humans and domestic animals (especially sheep and cattle) [1,2]. Galba pervia (Pulmonata: Lymnaeidae) is widely distributed and is the dominant host snail for transmission of Fasciola spp. in China [3]. Millions of humans have been infected by Fasciola spp. in a number of countries [8]. The metazoan mitochondrial (mt) genome, ranging in length from 14 to 18 kb, is typically circular and usually contains 36–37 genes, including 12–13 protein-coding genes, 2 ribosomal RNA (rRNA) genes and 22 transfer RNA (tRNA) genes [9]. Metazoan mt genome usually contains at least one lengthy noncoding region which is essential regulatory element for the initiation of transcription and replication [9]. Mitochondrial DNA (mtDNA) has long been extensively used as genetic markers to resolve evolutionary relationships among animal species due to their maternal inheritance, higher mutation rates than nuclear genes, and relatively conserved genome structures compared to ribosomal DNA [10,11,12,13,14,15]
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