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Ascidian mitogenomics: comparison of evolutionary rates in closely related taxa provides evidence of ongoing speciation events.

ABSTRACT: Ascidians are a fascinating group of filter-feeding marine chordates characterized by rapid evolution of both sequences and structure of their nuclear and mitochondrial genomes. Moreover, they include several model organisms used to investigate complex biological processes in chordates. To study the evolutionary dynamics of ascidians at short phylogenetic distances, we sequenced 13 new mitogenomes and analyzed them, together with 15 other available mitogenomes, using a novel approach involving detailed whole-mitogenome comparisons of conspecific and congeneric pairs. The evolutionary rate was quite homogeneous at both intraspecific and congeneric level, and the lowest congeneric rates were found in cryptic (morphologically undistinguishable) and in morphologically very similar species pairs. Moreover, congeneric nonsynonymous rates (dN) were up to two orders of magnitude higher than in intraspecies pairs. Overall, a clear-cut gap sets apart conspecific from congeneric pairs. These evolutionary peculiarities allowed easily identifying an extraordinary intraspecific variability in the model ascidian Botryllus schlosseri, where most pairs show a dN value between that observed at intraspecies and congeneric level, yet consistently lower than that of the Ciona intestinalis cryptic species pair. These data suggest ongoing speciation events producing genetically distinct B. schlosseri entities. Remarkably, these ongoing speciation events were undetectable by the cox1 barcode fragment, demonstrating that, at low phylogenetic distances, the whole mitogenome has a higher resolving power than cox1. Our study shows that whole-mitogenome comparative analyses, performed on a suitable sample of congeneric and intraspecies pairs, may allow detecting not only cryptic species but also ongoing speciation events.

SUBMITTER: Griggio F

PROVIDER: S-EPMC3971592 | biostudies-literature | 2014 Mar

REPOSITORIES: biostudies-literature

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Ascidian mitogenomics: comparison of evolutionary rates in closely related taxa provides evidence of ongoing speciation events.

Griggio Francesca F Voskoboynik Ayelet A Iannelli Fabio F Justy Fabienne F Tilak Marie-Ka MK Turon Xavier X Pesole Graziano G Douzery Emmanuel J P EJ Mastrototaro Francesco F Gissi Carmela C

Genome biology and evolution 20140301 3

Ascidians are a fascinating group of filter-feeding marine chordates characterized by rapid evolution of both sequences and structure of their nuclear and mitochondrial genomes. Moreover, they include several model organisms used to investigate complex biological processes in chordates. To study the evolutionary dynamics of ascidians at short phylogenetic distances, we sequenced 13 new mitogenomes and analyzed them, together with 15 other available mitogenomes, using a novel approach involving d ...[more]

PMID: 24572017

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Project description:BackgroundPueraria montana var. lobata (kudzu) is an important food and medicinal crop in Asia. However, the phylogenetic relationships between Pueraria montana var. lobata and the other two varieties (P. montana var. thomsonii and P. montana var. montana) remain debated. Although there is increasing evidence showing that P. montana var. lobata adapts to various environments and is an invasive species in America, few studies have systematically investigated the role of the phylogenetic relationships and evolutionary patterns of plastomes between P. montana var. lobata and its closely related taxa.Results26 newly sequenced chloroplast genomes of Pueraria accessions resulted in assembled plastomes with sizes ranging from 153,360 bp to 153,551 bp. Each chloroplast genome contained 130 genes, including eight rRNA genes, 37 tRNA genes, and 85 protein-coding genes. For 24 newly sequenced accessions of these three varieties of P. montana, we detected three genes and ten noncoding regions with higher nucleotide diversity (π). After incorporated publically available chloroplast genomes of Pueraria and other legumes, 47 chloroplast genomes were used to construct phylogenetic trees, including seven P. montana var. lobata, 14 P. montana var. thomsonii and six P. montana var. montana. Phylogenetic analysis revealed that P. montana var. lobata and P. montana var. thomsonii formed a clade, while all sampled P. montana var. montana formed another cluster based on cp genomes, LSC, SSC and protein-coding genes. Twenty-six amino acid residues were identified under positive selection with the site model. We also detected six genes (accD, ndhB, ndhC, rpl2, rpoC2, and rps2) that account for among-site variation in selective constraint under the clade model between accessions of the Pueraria montana var. lobata clade and the Pueraria montana var. montana clade.ConclusionOur data provide novel comparative plastid genomic insights into conservative gene content and structure of cp genomes pertaining to P. montana var. lobata and the other two varieties, and reveal an important phylogenetic clue and plastid divergence among related taxa of P. montana come from loci that own moderate variation and underwent modest selection.

Dataset Information

Ascidian mitogenomics: comparison of evolutionary rates in closely related taxa provides evidence of ongoing speciation events.

Publications

Ascidian mitogenomics: comparison of evolutionary rates in closely related taxa provides evidence of ongoing speciation events.

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