Fifteen species in one: deciphering the Brachionus plicatilis species complex (Rotifera, Monogononta) through DNA taxonomy

Understanding patterns and processes in biological diversity is a critical task given current and rapid environmental change. Such knowledge is even more essential when the taxa under consideration are important ecological and evolutionary models. One of these cases is the monogonont rotifer cryptic species complex Brachionus plicatilis, which is by far the most extensively studied group of rotifers, is widely used in aquaculture, and is known to host a large amount of unresolved diversity. Here we collate a dataset of previously available and newly generated sequences of COI and ITS1 for 1273 isolates of the B. plicatilis complex and apply three approaches in DNA taxonomy (i.e. ABGD, PTP, and GMYC) to identify and provide support for the existence of 15 species within the complex. We used these results to explore phylogenetic signal in morphometric and ecological traits, and to understand correlation among the traits using phylogenetic comparative models. Our results support niche conservatism for some traits (e.g. body length) and phylogenetic plasticity for others (e.g. genome size)

Reduction spheroids preserve a uranium isotope record of the ancient deep continental biosphere

S.M. acknowledges the support of the NASA Astrobiology Institute grant NNA13AA90A, Foundations of Complex Life, Evolution, Preservation and Detection on Earth and Beyond, and the European Union’s Horizon 2020 Research and Innovation Programme under Marie Skłodowska-Curie grant agreement 747877. Av.S.H. was supported by a NASA Astrobiology Institute Postdoctoral Fellowship and acknowledges the support of Xiangli Wang and Devon Cole for lab assistance. S.M. and Av.S.H. thank Noah Planavsky for technical advice, lab support, and comments on an early draft. J.P. was supported by NERC under grant number NE/L001764/1. The isotope facility at SUERC is supported by NERC. The authors thank the two anonymous referees for constructive criticisms that improved the manuscript.Peer reviewedPublisher PD

Matrix effects on the multi-collector inductively coupled plasma mass spectrometric analysis of high-precision cadmium and zinc isotope ratios.

Resin-derived contaminants added to samples during column chemistry are shown to cause matrix effects that lead to inaccuracy in multi-collector inductively coupled plasma mass spectrometry measurement of small natural variations in Cd and Zn isotopic compositions. These matrix effects were evaluated by comparing pure Cd and Zn standards and standards doped with bulk column blank from the anion exchange chromatography procedure. Doped standards exhibit signal enhancements (Cd, Ag, Zn and Cu), instrumental mass bias changes and inaccurate isotopic compositions relative to undoped standards, all of which are attributed to the combined presence of resin-derived organics and inorganics. The matrix effect associated with the inorganic component of the column blanks was evaluated separately by doping standards with metals at the trace levels detected in the column blanks. Mass bias effects introduced by the inorganic column blank matrix are smaller than for the bulk column blank matrix but can still lead to significant changes in ion signal intensity, instrumental mass bias and isotopic ratios. Chemical treatment with refluxed HNO(3) or HClO(4)/HNO(3) removes resin-derived organic components resulting in matrix effects similar in magnitude to those associated with the inorganic component of the column blank. Mass bias correction using combined external normalization-SSB does not correct for these matrix effects because the instrumental mass biases experienced by Cd and Zn are decoupled from those of Ag and Cu, respectively. Our results demonstrate that ion exchange chromatography and associated resin-derived contaminants can be a source of error in MC-ICP-MS measurement of heavy stable element isotopic compositions

Reactive transport of uranium in a groundwater bioreduction study: Insights from high-temporal resolution 238U/235U data

We conducted a detailed investigation of U isotopes in conjunction with a broad geochemical investigation during field-scale biostimulation and desorption experiments. This investigation was carried out in the uranium-contaminated alluvial aquifer of the Rifle field research site. In this well-characterized setting, a more comprehensive understanding of U isotope geochemistry is possible. Our results indicate that U isotope fractionation is consistently observed across multiple experiments at the Rifle site. Microbially-mediated reduction is suggested to account for most or all of the observed fractionation as abiotic reduction has been demonstrated to impart much smaller, often near-zero, isotopic fractionation or isotopic fractionation in the opposite direction. Data from some time intervals are consistent with a simple model for transport and U(VI) reduction, where the fractionation factor (ε = +0.65‰ to +0.85‰) is consistent with experimental studies. However, during other time intervals the observed patterns in our data indicate the importance of other processes in governing U concentrations and 238U/235U ratios. For instance, we demonstrate that departures from Rayleigh behavior in groundwater systems arise from the presence of adsorbed species. We also show that isotope data are sensitive to the onset of oxidation after biostimulation ends, even in the case where reduction continues to remove contaminant uranium downstream. Our study and the described conceptual model support the use of 238U/235U ratios as a tool for evaluating the efficacy of biostimulation and potentially other remedial strategies employed at Rifle and other uranium-contaminated sites

A new methodology for precise cadmium isotope analyses of seawater

Previous studies have revealed considerable Cdisotope fractionations in seawater, which can be used tostudy the marine cycling of this micronutrient element. Thelow Cd concentrations that are commonly encountered innutrient-depleted surface seawater, however, pose a particularchallenge for precise Cd stable isotope analyses. In thisstudy, we have developed a new procedure for Cd isotopeanalyses of seawater, which is suitable for samples as largeas 20 L and Cd concentrations as low as 1 pmol/L. Theprocedure involves the use of a 111Cd–113Cd double spike,co-precipitation of Cd from seawater using Al(OH)3, andsubsequent Cd purification by column chromatography. Tosave time, seawater samples with higher Cd contents can beprocessed without co-precipitation. The Cd isotope analysesare carried out by multiple collector inductively coupledplasma mass spectrometry (MC-ICP-MS). The performanceof this technique was verified by analyzing multiplealiquots of a large seawater sample that was collected fromthe English Channel, the SAFe D1 seawater referencematerial, and several samples from the GEOTRACESAtlantic intercalibration exercise. The overall Cd yield ofthe procedure is consistently better than 85% and themethodology can routinely provide ?114/110Cd data with aprecision of about ±0.5 ? (2sd, standard deviation) when atleast 20–30 ng of natural Cd is available for analysis.However, even seawater samples with Cd contents of only1–3 ng can be analyzed with a reproducibility of about ±3to ±5 ?. A number of experiments were furthermoreconducted to verify that the isotopic results are accurate to within the quoted uncertainty