Modelling mitochondrial site polymorphisms to infer the number of segregating units and mutation rate

We present a mathematical model of mitochondrial inheritance evolving under neutral evolution to interpret the heteroplasmies observed at some sites. A comparison of the levels of heteroplasmies transmitted from mother to her offspring allows us to estimate the number Nx of inherited mitochondrial genomes (segregating units). The model demonstrates the necessity of accounting for both the multiplicity of an unknown number Nx, and the threshold θ, below which heteroplasmy cannot be detected reliably, in order to estimate the mitochondrial mutation rate μm in the maternal line of descent. Our model is applicable to pedigree studies of any eukaryotic species where site heteroplasmies are observed in regions of the mitochondria, provided neutrality can be assumed. The model is illustrated with an analysis of site heteroplasmies in the first hypervariable region of mitochondrial sequence data sampled from Adélie penguin families, providing an estimate Nx and μm. This estimate of μm was found to be consistent with earlier estimates from ancient DNA analysis

Integrating DNA and morphological taxonomy to describe diversity in poorly studied microscopic animals: new species of the genus Abrochtha Bryce, 1910 (Rotifera: Bdelloidea: Philodinavidae)

Specimens of the bdelloid rotifer genus Abrochtha were collected from mountain and desert sites in the western USA. All were morphologically distinct from the two previously described species of this genus. Barcode sequences of the cytochrome c oxidase subunit I (COI) gene were obtained from 14 specimens. These were shown to be samples from four different independently evolving populations or metapopulations, i.e. evolutionary species. Two different species criteria rooted in population and evolutionary genetic theory, the 4\ua5 rule and the generalized mixed yule coalescent (GMYC) method, agreed in the delimitation of the four species. Three of these evolutionary species are formally described as new species; two are cryptic species, differentiable only by statistical analysis of morphometric data. This is the first time that these species criteria have been used in new species descriptions, and the first formal descriptions of cryptic bdelloid species delimited by molecular analyses