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- Lartillot, Nicolas, et al.
(författare)
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A mixed relaxed clock model
- 2016
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 371
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Tidskriftsartikel (refereegranskat)abstract
- Over recent years, several alternative relaxed clock models have been proposed in the context of Bayesian dating. These models fall in two distinct categories: uncorrelated and autocorrelated across branches. The choice between these two classes of relaxed clocks is still an open question. More fundamentally, the true process of rate variation may have both long-term trends and short-term fluctuations, suggesting that more sophisticated clock models unfolding over multiple time scales should ultimately be developed. Here, a mixed relaxed clock model is introduced, which can be mechanistically interpreted as a rate variation process undergoing short-term fluctuations on the top of Brownian long-term trends. Statistically, this mixed clock represents an alternative solution to the problem of choosing between autocorrelated and uncorrelated relaxed clocks, by proposing instead to combine their respective merits. Fitting this model on a dataset of 105 placental mammals, using both node-dating and tip-dating approaches, suggests that the two pure clocks, Brownian and white noise, are rejected in favour of a mixed model with approximately equal contributions for its uncorrelated and autocorrelated components. The tip-dating analysis is particularly sensitive to the choice of the relaxed clock model. In this context, the classical pure Brownian relaxed clock appears to be overly rigid, leading to biases in divergence time estimation. By contrast, the use of a mixed clock leads to more recent and more reasonable estimates for the crown ages of placental orders and superorders. Altogether, the mixed clock introduced here represents a first step towards empirically more adequate models of the patterns of rate variation across phylogenetic trees.This article is part of the themed issue ‘Dating species divergences using rocks and clocks’.
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- Ronquist, Fredrik, 1962-, et al.
(författare)
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Closing the gap between rocks and clocks using total-evidence dating
- 2016
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 371
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Tidskriftsartikel (refereegranskat)abstract
- Total-evidence dating (TED) allows evolutionary biologists to incorporate a wide range of dating information into a unified statistical analysis. One might expect this to improve the agreement between rocks and clocks but this is not necessarily the case. We explore the reasons for such discordance using a mammalian dataset with rich molecular, morphological and fossil information. There is strong conflict in this dataset between morphology and molecules under standard stochastic models. This causes TED to push divergence events back in time when using inadequate models or vague priors, a phenomenon we term ‘deep root attraction’ (DRA). We identify several causes of DRA. Failure to account for diversified sampling results in dramatic DRA, but this can be addressed using existing techniques. Inadequate morphological models also appear to be a major contributor to DRA. The major reason seems to be that current models do not account for dependencies among morphological characters, causing distorted topology and branch length estimates. This is particularly problematic for huge morphological datasets, which may contain large numbers of correlated characters. Finally, diversification and fossil sampling priors that do not incorporate all the available background information can contribute to DRA, but these priors can also be used to compensate for DRA. Specifically, we show that DRA in the mammalian dataset can be addressed by introducing a modest extra penalty for ghost lineages that are unobserved in the fossil record, for instance by assuming rapid diversification, rare extinction or high fossil sampling rate; any of these assumptions produces highly congruent divergence time estimates with a minimal gap between rocks and clocks. Under these conditions, fossils have a stabilizing influence on divergence time estimates and significantly increase the precision of those estimates, which are generally close to the dates suggested by palaeontologists.This article is part of the themed issue ‘Dating species divergences using rocks and clocks’.
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- Ronquist, Fredrik, 1962-, et al.
(författare)
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EU-BON Deliverable 1.3. Systems for mobilizing and managing collection-based data (specimen + DNA-data) fully integrated
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Introduction. A large portion of the biodiversity data in natural history collections is still not available digitally. Increasingly, innovative high-throughput methods are being applied to digitize this backlog in bulk, generating large amounts of data. In parallel, natural history museums are becoming increasingly involved in the generation of large amounts of molecular biodiversity data using new massively parallel sequencing platforms. Against this backdrop, the goal of EU BON Task 1.4 has been to support data mobilization efforts targeting collection-based and molecular data, mainly through the development and integration of innovative open-source tools and services.Progress towards objectives. The activities have involved work within the context of three major projects: i) DINA, an open-source, modular, web-based collection management system for natural history specimen data. ii) JACQ an open-access system for botanical (herbarium) data. iii) PlutoF, a web platform for working with traditional and molecular biodiversity research data. The task has also involved work on a number of other EU BON partner systems and services, as well as integration across internal EU BON and external biodiversity informatics resources. Finally, these systems have been used for targeted data mobilization efforts.Achievements and current status. Within DINA, the focus has been on supporting the engineering of sophisticated biodiversity information systems through the exploration of tools supporting distributed development and a modular plug-and-play design based on services-oriented architectures. This has involved the testing and adoption of tools like Apiary for the design of Application Programming Interfaces (APIs) and Docker for systems integration and deployment tasks. A Python library for data migration to DINA was also developed and tested. Within JACQ, a number of tools were developed to facilitate deployment and data migration to the system, and the AnnoSys tool for annotation of data has been integrated. Within PlutoF, EU BON efforts focused on the development of a citizen-science module and improved functionality for the mobilization of collection (living) specimen data. A number of innovative tools were developed by Pensoft to help mobilize biodiversity data published in the scientific literature, including semantic mark-up of species conservation papers, direct import of data from a range of biodiversity platforms into manuscripts, and a mechanism for providing stable links from publications to global biodiversity repositories. Plazi implemented an automated workflow mining published scientific papers for taxonomic data, currently mobilizing 25 % of all published new names as they become available. GlueCad developed apps allowing citizen scientists reporting spontaneous observations or systematic inventory data to select target taxa and preferred data mobilization platform. IBSAS and UCPH have focused on national data mobilization efforts targeting Slovakia and Denmark, respectively.Future developments. Although the development is clearly towards increased integration of biodiversity informatics tools into larger and more sophisticated systems, it is clear that there is no one size that fits all. Nevertheless, the increasingly widespread adoption of community standards, open-source development practises and service-oriented architectures are pushing the capability of current systems forward and facilitating tighter integration across systems. This trend is supported by the appearance of sophisticated tools enabling the design and deployment of complex modular systems. The adoption of the Docker approach is one example of how the biodiversity informatics community may benefit from this.
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