Mécanismes de prise en charge su sélénite - Se (IV) - chez l'algue verte unicellulaire Chlamydomonas reinhardtii. Bioaccumulation et effets induits sur la croissance et l'ultrastructure

Le sélénium est un élément essentiel, mais qui devient très toxique à des concentrations plus élevées. Il est présent dans l’environnement à des concentrations variant du nM au µM et la pollution par cet élément est un phénomène mondial. Ce travail vise à accroître les connaissances relatives à l’interaction entre le sélénite -Se(IV)- et un organisme phytoplanctonique d’eau douce : l’algue verte unicellulaire Chlamydomonas reinhardtii. Les objectifs des expériences réalisées étaient : i) d’étudier les mécanismes de prise en charge du sélénite, à l’aide d’expositions de courte durée ( µM), suggérant qu’un transport de haute affinité mais rapidement saturé pourrait intervenir à faibles concentrations, doublé par un transport de faible affinité qui ne saturerait qu’à fortes concentrations (~mM). Ce dernier pourrait faire intervenir les transporteurs du sulfate et du nitrate, comme le suggère l’inhibition de la prise en charge du sélénite par ces éléments. Les modifications de spéciation du Se(IV) avec le pH n’ont à priori pas induit d’effet significatif sur la biodisponibilité. Sur la base de la relation entre concentration en Se et densité cellulaire maximale atteinte, nous avons calculé une EC50 de 80 µM ([64; 98]). Nous n’avons pas mis en évidence de mécanismes d’adaptation, avec une toxicité similaire pour des algues pré-exposées ou non au sélénite. Les observations au MET ont suggéré que le chloroplaste soit la première cible de la cytotoxicité de l’élément, avec des effets sur le stroma, les thylakoïdes et le pyrénoïde. Aux concentrations les plus élevées, nous avons observé une augmentation du nombre et du volume des grains d’amidon, ainsi que la formation de granules denses aux électrons. Les analyses en spectrométrie par dispersion en énergie ont montré que ceux-ci contenaient du sélénium et étaient également riches en calcium et phosphore. Nous avons montré que l’inhibition de croissance était fortement corrélée à la bioaccumulation, et que cette dernière était inhibée par des concentrations croissantes en sulfate. Enfin, le facteur de concentration, calculé sur la base du poids sec, variait entre 690 et 7100.Selenium is an essential element, but becomes very toxic at higher concentrations. It occurs in the environment at concentrations ranging from nM to µM and selenium pollution is a worldwide phenomenon. This work aims at improving the knowledge on the interactions between selenite - Se(IV) - and a freshwater phytoplanktonic organism : the unicellular green algae Chlamydomonas reinhardtii. The aim of the performed experiments were : i) to investigate selenite -Se(IV°)- uptake mechanisms in C. reinhardtii, using Se75 as a radiotracer in short-term exposures ( µM), suggesting that a high affinity but rapidly saturated transport mechanism could be used at low concentrations, in parallel with a low affinity mechanism that would only saturate at high concentrations (~mM). The latter could involve transporters used by sulphate and nitrate, as suggested by the inhibition of selenite uptake by those elements. Se(IV) speciation changes with pH did not induce significant effect on bioavailability. On the basis of the relationship between Se concentration and maximal cell density achieved, an EC50 of 80 µM ([64; 98]) was derived. No adaptation mechanisms were observed as the same toxicity was quantified for Se-pre-exposed algae. Observations by TEM suggested chloroplasts as the first target of selenite cytotoxicity, with effects on the stroma, thylakoids and pyrenoids. At higher concentrations, we could observe an increase in the number and volume of starch grains. For cells collected at 96 h, electron-dense granules were observed. Energy-dispersive X-ray microanalysis revealed that they contained selenium and were also rich in calcium and phosphorus. Finally, growth inhibition was highly correlated to the bioaccumulation of selenite. The latter was inhibited by increasing concentrations of sulphate, and calculated dry weight concentration factors varied between 690 and 7100

Inferring the Dynamics of Diversification: A Coalescent Approach

A novel approach to infer diversification dynamics shows that biodiversity is still expanding but at a slower rate than in the past

Pengaruh Keaktifan Siswa terhadap Prestasi Belajar Mata Pelajaran Akuntansi Mengelola Kartu Utang pada Siswa Kelas XI Akuntansi

Penelitian ini bertujuan untuk mengetahui seberapa besar Pengaruh Keaktifan Siswa terhadap Prestasi Belajar Mata Pelajaran Akuntansi Mengelola Kartu Utang pada Siswa Kelas XI Akuntansi SMK Negeri 1 Makassar. Penelitian ini merupakan jenis penelitian kuantitatif. Populasinya adalah seluruh siswa kelas XI Akuntansi SMK Negeri 1 Makassar tahun ajaran 2014/2015 yang berjumlah 139 orang, dan sampelnya berjumlah 80 orang. Teknik pengumpulan data yang digunakan adalah kuesioner dan dokumentasi.Teknik analisis data dilakukan dengan menggunakan analisis keabsahan data dan analisis statistik data dengan menggunakan program SPSS 20 for windows. Hasil persamaan regresi linear sederhana yang diperoleh antara keaktifan Siswa dan prestasi belajar yaitu = 50,918 + 0,390X. Koefisien bernilai positif artinya terjadi hubungan positif antara keaktifan siswa dengan prestasi belajar. Berdasarkan koefisien korelasi diperoleh nilai r=0,600. Nilai tersebut menunjukkan hubungan dalam kategori kuat. Sedangkan koefisien determinasi (r2) = 0,360atau36% yang berarti bahwa kontribusi keaktifan siswa terhadap prestasi belajar sebesar 36%, sedangkan sisanya sebesar 64% ditentukan oleh faktor lain diluar faktor yang diteliti dalam penelitian ini.Dari hasil perhitungan uji-t di peroleh nilai t-hitung= 6,624 lebih besar dari pada t- tabel=1,668. Hal ini berarti hipotesis yang bunyinya “keaktifan siswa berpengaruh positif dan signifikan terhadap prestasi belajar mata pelajaran akuntansi mengelola kartu utang pada siswa kelas XI Akuntansi SMK Negeri 1 Makassar” diterima. Dari hasil yang telah diperoleh maka dapat disimpulkan bahwa keaktifan siswa berpengaruh positif dan signifikan terhadap prestasi belajar mata pelajaran akuntansi mengelola kartu utang pada siswa kelas XI Akuntansi SMK Negeri 1 Makassar. Kata kunci : Keaktifan Siswa, Prestasi Belajar Akuntansi Mengelola Kartu Utan

Do closely related species interact with similar partners? Testing for phylogenetic signal in bipartite interaction networks

Whether interactions between species are conserved on evolutionary time-scales has spurred the development of both correlative and process-based approaches for testing phylogenetic signal in interspecific interactions: do closely related species interact with similar partners? Here we use simulations to test the statistical performances of the two approaches that are the most widely used in the field: Mantel tests and the Phylogenetic Bipartite Linear Model (PBLM). Mantel tests investigate the correlation between phylogenetic distances and dissimilarities in sets of interacting partners, while PBLM is a process-based approach that relies on strong assumptions about how interactions evolve. We find that PBLM often detects a phylogenetic signal when it should not. Simple Mantel tests instead have infrequent false positives and moderate statistical power; however, they often artifactually detect that closely related species interact with dissimilar partners. Partial Mantel tests, which are used to partial out the phylogenetic signal in the number of partners, actually fail at correcting for this confounding effect, and we instead recommend evaluating the significance of Mantel tests with network permutations constraining the number of partners. We also explore the ability of simple Mantel tests to analyze clade-specific phylogenetic signals. We provide general guidelines and an application on an interaction network between orchids and mycorrhizal fungi.ecological network, phylogenetic signal, Mantel tests, clade-specific signal, species interactions, mycorrhizal symbiosis

Integrating ecology into macroevolutionary research

On 9 March, over 150 biologists gathered in London for the Centre for Ecology and Evolution spring symposium, ‘Integrating Ecology into Macroevolutionary Research’. The event brought together researchers from London-based institutions alongside others from across the UK, Europe and North America for a day of talks. The meeting highlighted methodological advances and recent analyses of exemplar datasets focusing on the exploration of the role of ecological processes in shaping macroevolutionary patterns

Coming of age for COI metabarcoding of whole organism community DNA: towards bioinformatic harmonisation

Metabarcoding of DNA extracted from community samples of whole organisms (whole organism community DNA, wocDNA) is increasingly being applied to terrestrial, marine and freshwater metazoan communities to provide rapid, accurate and high resolution data for novel molecular ecology research. The growth of this field has been accompanied by considerable development that builds on microbial metabarcoding methods to develop appropriate and efficient sampling and laboratory protocols for whole organism metazoan communities. However, considerably less attention has focused on ensuring bioinformatic methods are adapted and applied comprehensively in wocDNA metabarcoding. In this study we examined over 600 papers and identified 111 studies that performed COI metabarcoding of wocDNA. We then systematically reviewed the bioinformatic methods employed by these papers to identify the state-of-the-art. Our results show that the increasing use of wocDNA COI metabarcoding for metazoan diversity is characterised by a clear absence of bioinformatic harmonisation, and the temporal trends show little change in this situation. The reviewed literature showed (i) high heterogeneity across pipelines, tasks and tools used, (ii) limited or no adaptation of bioinformatic procedures to the nature of the COI fragment, and (iii) a worrying underreporting of tasks, software and parameters. Based upon these findings we propose a set of recommendations that we think the metabarcoding community should consider to ensure that bioinformatic methods are appropriate, comprehensive and comparable. We believe that adhering to these recommendations will improve the long-term integrative potential of wocDNA COI metabarcoding for biodiversity science

Macroevolution of the plant–hummingbird pollination system

ABSTRACTPlant–hummingbird interactions are considered a classic example of coevolution, a process in which mutually dependent species influence each other's evolution. Plants depend on hummingbirds for pollination, whereas hummingbirds rely on nectar for food. As a step towards understanding coevolution, this review focuses on the macroevolutionary consequences of plant–hummingbird interactions, a relatively underexplored area in the current literature. We synthesize prior studies, illustrating the origins and dynamics of hummingbird pollination across different angiosperm clades previously pollinated by insects (mostly bees), bats, and passerine birds. In some cases, the crown age of hummingbirds pre‐dates the plants they pollinate. In other cases, plant groups transitioned to hummingbird pollination early in the establishment of this bird group in the Americas, with the build‐up of both diversities coinciding temporally, and hence suggesting co‐diversification. Determining what triggers shifts to and away from hummingbird pollination remains a major open challenge. The impact of hummingbirds on plant diversification is complex, with many tropical plant lineages experiencing increased diversification after acquiring flowers that attract hummingbirds, and others experiencing no change or even a decrease in diversification rates. This mixed evidence suggests that other extrinsic or intrinsic factors, such as local climate and isolation, are important covariables driving the diversification of plants adapted to hummingbird pollination. To guide future studies, we discuss the mechanisms and contexts under which hummingbirds, as a clade and as individual species (e.g. traits, foraging behaviour, degree of specialization), could influence plant evolution. We conclude by commenting on how macroevolutionary signals of the mutualism could relate to coevolution, highlighting the unbalanced focus on the plant side of the interaction, and advocating for the use of species‐level interaction data in macroevolutionary studies

Into the Andes: multiple independent colonizations drive montane diversity in the Neotropical clearwing butterflies Godyridina.

Understanding why species richness peaks along the Andes is a fundamental question in the study of Neotropical biodiversity. Several biogeographic and diversification scenarios have been proposed in the literature, but there is confusion about the processes underlying each scenario, and assessing their relative contribution is not straightforward. Here, we propose to refine these scenarios into a framework which evaluates four evolutionary mechanisms: higher speciation rate in the Andes, lower extinction rates in the Andes, older colonization times and higher colonization rates of the Andes from adjacent areas. We apply this framework to a species-rich subtribe of Neotropical butterflies whose diversity peaks in the Andes, the Godyridina (Nymphalidae: Ithomiini). We generated a time-calibrated phylogeny of the Godyridina and fitted time-dependent diversification models. Using trait-dependent diversification models and ancestral state reconstruction methods we then compared different biogeographic scenarios. We found strong evidence that the rates of colonization into the Andes were higher than the other way round. Those colonizations and the subsequent local diversification at equal rates in the Andes and in non-Andean regions mechanically increased the species richness of Andean regions compared to that of non-Andean regions ('species-attractor' hypothesis). We also found support for increasing speciation rates associated with Andean lineages. Our work highlights the importance of the Andean slopes in repeatedly attracting non-Andean lineages, most likely as a result of the diversity of habitats and/or host plants. Applying this analytical framework to other clades will bring important insights into the evolutionary mechanisms underlying the most species-rich biodiversity hotspot on the planet

Embracing heterogeneity: coalescing the Tree of Life and the future of phylogenomics

Building the Tree of Life (ToL) is a major challenge of modern biology, requiring advances in cyberinfrastructure, data collection, theory, and more. Here, we argue that phylogenomics stands to benefit by embracing the many heterogeneous genomic signals emerging from the first decade of large-scale phylogenetic analysis spawned by high-throughput sequencing (HTS). Such signals include those most commonly encountered in phylogenomic datasets, such as incomplete lineage sorting, but also those reticulate processes emerging with greater frequency, such as recombination and introgression. Here we focus specifically on how phylogenetic methods can accommodate the heterogeneity incurred by such population genetic processes; we do not discuss phylogenetic methods that ignore such processes, such as concatenation or supermatrix approaches or supertrees. We suggest that methods of data acquisition and the types of markers used in phylogenomics will remain restricted until a posteriori methods of marker choice are made possible with routine whole-genome sequencing of taxa of interest. We discuss limitations and potential extensions of a model supporting innovation in phylogenomics today, the multispecies coalescent model (MSC). Macroevolutionary models that use phylogenies, such as character mapping, often ignore the heterogeneity on which building phylogenies increasingly rely and suggest that assimilating such heterogeneity is an important goal moving forward. Finally, we argue that an integrative cyberinfrastructure linking all steps of the process of building the ToL, from specimen acquisition in the field to publication and tracking of phylogenomic data, as well as a culture that values contributors at each step, are essential for progress