Patterns and rules for sensitivity and elasticity in population projection matrices

Sensitivity and elasticity analysis of population projection matrices (PPMs) are established tools in the analysis of structured populations, allowing comparison of the contributions made by different demographic rates to population growth. In some commonly used structures of PPM, however, there are mathematically inevitable patterns in the relative sensitivity and elasticity of certain demographic rates. We take a simulation approach to investigate these mathematical constraints for a range of PPM models. Our results challenge some previously proposed constraints on sensitivity and elasticity. We also identify constraints beyond those which have already been proven mathematically, and promote them as candidates for future mathematical proof. A general theme among these rules is that changes to the demographic rates of older or larger individuals have less impact on population growth than do equivalent changes among younger or smaller individuals. However, the validity of these rules in each case depends on the choice between sensitivity and elasticity, the growth rate of the population and the PPM structure used. If the structured population conforms perfectly to the assumptions of the PPM used to model it, the rules we describe represent biological reality, allowing us to prioritise management strategies in the absence of detailed demographic data. Conversely, if the model is a poor fit to the population (specifically; if demographic rates within stages are heterogeneous) such analyses could lead to inappropriate management prescriptions. Our results emphasise the importance of choosing a structured population model which fits the demographics of the population

An economic analysis of trading on private information by external administrators: international comparisons

This paper examines the regulation of trades in listed securities by external administrators (EAs), such as trustees in bankruptcy, liquidators, receivers, and administrators on the basis of private information. We consider the economic policy issues associated with such trades. The principal considerations counsel in favour of taking a permissive approach. These are: the difficulties of associating trades with insider information, given the EA's necessarily short expected holding period, the asymmetric application of the insider trading prohibition to sales (rather than decisions not to sell), the market incentives not to misuse private information that apply to EAs, and the unlikelihood that the EA has monopolistic access to the information in question. We consider these considerations by reference to a number of hypothetical scenarios. The paper argues that the law should regulate the subject by coupling a broad exemption for EAs with a "goiod faith" proviso, a continuous disclosure obligation, and a requirement to sell "all or nothing" of a holding of listed securities

Why do sperm carry RNA? Relatedness, conflict, and control

Classically, sperm were seen as transcriptionally inactive vehicles for delivering the paternal haplotype to an egg. Yet, it has become apparent that sperm also carry thousands of different RNAs, and the functions of most of these are unknown. Here, we make four novel suggestions for sperm RNA function. First, they could act as relatedness markers facilitating sperm cooperation. Second, they could act as paternally imposed suppressors of haploid interests. Third, they could act as a nuptial gift, providing the female with resources that entice her to fertilise ova using the sperm of the gift-provider. Fourth, they could represent the contents of a Trojan horse, delivered by males to manipulate female reproduction. We discuss these ideas and suggest how they might be tested

Epithelial organization and cyst lumen expansion require efficient Sec13-Sec31-driven secretion

Epithelial morphogenesis is directed by interactions with the underlying extracellular matrix. Secretion of collagen and other matrix components requires efficient coat complex II (COPII) vesicle formation at the endoplasmic reticulum. Here, we show that suppression of the outer layer COPII component, Sec13, in zebrafish embryos results in a disorganized gut epithelium. In human intestinal epithelial cells (Caco-2), Sec13 depletion causes defective epithelial polarity and organization on permeable supports. Defects are seen in the ability of cells to adhere to the substrate, form a monolayer and form intercellular junctions. When embedded in a three-dimensional matrix, Sec13-depleted Caco-2 cells form cysts but, unlike controls, are defective in lumen expansion. Incorporation of primary fibroblasts within the three-dimensional culture substantially restores normal morphogenesis. We conclude that efficient COPII-dependent secretion, notably assembly of Sec13–Sec31, is required to drive epithelial morphogenesis in both two- and three-dimensional cultures in vitro, as well as in vivo. Our results provide insight into the role of COPII in epithelial morphogenesis and have implications for the interpretation of epithelial polarity and organization assays in cell culture

Social evolution of toxic metal bioremediation in Pseudomonas aeruginosa

This is the final version. Available on open access from the Royal Society via the DOI in this recordThere is another ORE record for this publication: http://hdl.handle.net/10871/39858Bacteria are often iron-limited, and hence produce extracellular iron-scavenging siderophores. A crucial feature of siderophore production is that it can be an altruistic behaviour (individually costly but benefitting neighbouring cells), thus siderophore producers can be invaded by non-producing social ‘cheats’. Recent studies have shown that siderophores can also bind other heavy metals (such as Cu and Zn), but in this case siderophore chelation actually reduces metal uptake by bacteria. These complexes reduce heavy metal toxicity, hence siderophore production may contribute to toxic metal bioremediation. Here, we show that siderophore production in the context of bioremediation is also an altruistic trait and can be exploited by cheating phenotypes in the opportunistic pathogen Pseudomonas aeruginosa. Specifically, we show that in toxic copper concentrations (i) siderophore non-producers evolve de novo and reach high frequencies, and (ii) producing strains are fitter than isogenic non-producing strains in monoculture, and vice versa in co-culture. Moreover, we show that the evolutionary effect copper has on reducing siderophore production is greater than the reduction observed under iron-limited conditions. We discuss the relevance of these results to the evolution of siderophore production in natural communities and heavy metal bioremediation.AXANERCUniversity of Exete

Development and testing of a risk indexing framework to determine field-scale critical source areas of faecal bacteria on grassland.

This paper draws on lessons from a UK case study in the management of diffuse microbial pollution from grassland farm systems in the Taw catchment, south west England. We report on the development and preliminary testing of a field-scale faecal indicator organism risk indexing tool (FIORIT). This tool aims to prioritise those fields most vulnerable in terms of their risk of contributing FIOs to water. FIORIT risk indices were related to recorded microbial water quality parameters (faecal coliforms [FC] and intestinal enterococci [IE]) to provide a concurrent on-farm evaluation of the tool. There was a significant upward trend in Log[FC] and Log[IE] values with FIORIT risk score classification (r2 =0.87 and 0.70, respectively and P<0.01 for both FIOs). The FIORIT was then applied to 162 representative grassland fields through different seasons for ten farms in the case study catchment to determine the distribution of on-farm spatial and temporal risk. The high risk fields made up only a small proportion (1%, 2%, 2% and 3% for winter, spring, summer and autumn, respectively) of the total number of fields assessed (and less than 10% of the total area), but the likelihood of the hydrological connection of high FIO source areas to receiving watercourses makes them a priority for mitigation efforts. The FIORIT provides a preliminary and evolving mechanism through which we can combine risk assessment with risk communication to end-users and provides a framework for prioritising future empirical research. Continued testing of FIORIT across different geographical areas under both low and high flow conditions is now needed to initiate its long term development into a robust indexing tool

The potential for vaccination-induced herd immunity against the SARS-CoV-2 B.1.1.7 variant

Initial reports of vaccine effectiveness against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for coronavirus disease (COVID-19), have suggested a substantial reduction of the risk of infection [1]. Nevertheless, with the emergence of more transmissible variants such as B.1.1.7 [2], how large-scale immunisation programmes against SARS-CoV-2 will perform is currently unclear. This study assesses the potential of COVID-19 vaccination to generate herd immunity and takes into account vaccine effectiveness, naturally-acquired immunity and achievable vaccination coverage (depending on the population age structure), as well as two transmissibility scenarios ((i) with pre-B.1.1.7, and (ii) with exclusively B.1.1.7 variants)

Of Student Teachers and Avatars: Working Towards an Effective Model for Geographically Distributed Learning Communities of Pre-Service Educators Using Virtual Worlds.

With greater distribution of learning communities through the expanding use of online and distance learning, researchers emphasize focus on the effective use of specific technologies on student preference and achievement. One such technology drawing significant interest in scholarly and practical circles is the use of Multi-User Virtual Environments (MUVE), with the more common environment being Second Life, a product of Linden Labs, This research project, having gone through a pilot stage and under current implementation, addresses preference and effectiveness through a mixed-method research endeavor, examining forming communities using Second Life’s environment for small group discussions and large group seminar presentations for pre-service student teachers in a teacher education program. Methods of data collection and analysis include survey comparative analysis (using Keller’s Instructional Materials Motivation Survey and Rovai’s Community Survey Instrument), observation, semi-structured interview and comparative analysis of achievement on a content-based assessment

Sexual and natural selection both influence male genital evolution.

Published onlineJournal ArticleResearch Support, Non-U.S. Gov'tRapid and divergent evolution of male genital morphology is a conspicuous and general pattern across internally fertilizing animals. Rapid genital evolution is thought to be the result of sexual selection, and the role of natural selection in genital evolution remains controversial. However, natural and sexual selection are believed to act antagonistically on male genital form. We conducted an experimental evolution study to investigate the combined effects of natural and sexual selection on the genital-arch lobes of male Drosophila simulans. Replicate populations were forced to evolve under lifetime monogamy (relaxed sexual selection) or lifetime polyandry (elevated sexual selection) and two temperature regimes, 25°C (relaxed natural selection) or 27°C (elevated natural selection) in a fully factorial design. We found that natural and sexual selection plus their interaction caused genital evolution. Natural selection caused some aspects of genital form to evolve away from their sexually selected shape, whereas natural and sexual selection operated in the same direction for other shape components. Additionally, sexual and natural selection tended to favour larger genitals. Thus we find that the underlying selection driving genital evolution is complex, does not only involve sexual selection, and that natural selection and sexual selection do not always act antagonistically.NERCLeverhulme TrustRoyal Societ

A revised position for the rotated Falkland Islands microplate

The early stages of transform margin formation are associated with crustal fragmentation and block rotation. The restricted size of the resultant microcontinental blocks precludes palaeogeographical reconstructions and reliable estimations of the amount of rotation they can undergo. An example considered here is the Falkland Plateau. This is located adjacent to the Agulhas–Falkland Fracture Zone and its westernmost province is the Falkland Islands microcontinent. The position of the plateau and the islands prior to Gondwana break-up remains contentious. This study integrates seismic reflection and gravity data to propose a revised position of the Falkland Islands microcontinent constrained by (1) the presence of a mega-décollement, controlling the Gondwanide Orogen, described north of the Falkland Islands and underneath South Africa and the Outeniqua Basin, and (2) the similar architecture of fault networks mapped north of the islands and in the northernmost Outeniqua Basin. This revised position requires a re-evaluation of the timing and rate of rotation of the Falkland Islands microcontinent and affects the expected crustal architecture adjacent to the islands. Our model yields rotation rates between 5.5° and 8° Ma−1 and two potential times for rotation, and predicts more unstretched crust beneath the basin east of the Falkland Islands than previous model