Abstract
Mitochondrial genomes (mitogenomes) are useful and relatively accessible sources of molecular data to explore and understand the evolutionary history and relationships of eukaryotic organisms across diverse taxonomic levels. The availability of complete mitogenomes from Platyhelminthes is limited; of the 40 or so published most are from parasitic flatworms (Neodermata). Here, we present the mitogenomes of two free-living flatworms (Tricladida): the complete genome of the freshwater species Crenobia alpina (Planariidae) and a nearly complete genome of the land planarian Obama sp. (Geoplanidae). Moreover, we have reanotated the published mitogenome of the species Dugesia japonica (Dugesiidae). This contribution almost doubles the total number of mtDNAs published for Tricladida, a species-rich group including model organisms and economically important invasive species. We took the opportunity to conduct comparative mitogenomic analyses between available free-living and selected parasitic flatworms in order to gain insights into the putative effect of life cycle on nucleotide composition through mutation and natural selection. Unexpectedly, we did not find any molecular hallmark of a selective relaxation in mitogenomes of parasitic flatworms; on the contrary, three out of the four studied free-living triclad mitogenomes exhibit higher A+T content and selective relaxation levels. Additionally, we provide new and valuable molecular data to develop markers for future phylogenetic studies on planariids and geoplanids.
Highlights
Complete mitochondrial genomes provide a diversity of molecular markers suitable to study a variety of biological features, including the effects of different life habits (e.g. [1]) or the phylogenetic relationships among populations or species
The complete mitochondrial genomes of two triclads and eight neodermatans were retrieved from GenBank (Table 1) to carry out a preliminary gene checking of the mitogenomes obtained in this study by means of 454 (Roche) pyrosequencing, and to perform analytical comparisons between triclads and parasitic flatworms
We found differences between the expected and predicted translation for some codons; one or two for Obama sp. and one to five for Crenobia alpina depending on the degree of Shannon entropy
Summary
Complete mitochondrial genomes (mitogenomes) provide a diversity of molecular markers suitable to study a variety of biological features, including the effects of different life habits (e.g. [1]) or the phylogenetic relationships among populations or species. [1]) or the phylogenetic relationships among populations or species. Complete mitochondrial genomes (mitogenomes) provide a diversity of molecular markers suitable to study a variety of biological features, including the effects of different life habits This is because mitochondrial (mt) DNA does not usually recombine, commonly exhibits neutral evolution, and mt markers have smaller effective population sizes than their nuclear counterparts which result in PLOS ONE | DOI:10.1371/journal.pone.0120081. Tricladida vs Parasitic Platyhelminthes Mitogenomes collection and analysis, decision to publish, or preparation of the manuscript This is because mitochondrial (mt) DNA does not usually recombine, commonly exhibits neutral evolution, and mt markers have smaller effective population sizes than their nuclear counterparts which result in PLOS ONE | DOI:10.1371/journal.pone.0120081 March 20, 2015
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