Diversity and recombination of dispersed ribosomal DNA and protein coding genes in microsporidia

Microsporidian strains are usually classified on the basis of their ribosomal DNA (rDNA) sequences. Although rDNA occurs as multiple copies, in most non-microsporidian species copies within a genome occur as tandem arrays and are homogenised by concerted evolution. In contrast, microsporidian rDNA units are dispersed throughout the genome in some species, and on this basis are predicted to undergo reduced concerted evolution. Furthermore many microsporidian species appear to be asexual and should therefore exhibit reduced genetic diversity due to a lack of recombination. Here, DNA sequences are compared between microsporidia with different life cycles in order to determine the effects of concerted evolution and sexual reproduction upon the diversity of rDNA and protein coding genes. Comparisons of cloned rDNA sequences between microsporidia of the genus Nosema with different life cycles provide evidence of intragenomic variability coupled with strong purifying selection. This suggests a birth and death process of evolution. However, some concerted evolution is suggested by clustering of rDNA sequences within species. Variability of protein-coding sequences indicates that considerable intergenomic variation also occurs between microsporidian cells within a single host. Patterns of variation in microsporidian DNA sequences indicate that additional diversity is generated by intragenomic and/or intergenomic recombination between sequence variants. The discovery of intragenomic variability coupled with strong purifying selection in microsporidian rRNA sequences supports the hypothesis that concerted evolution is reduced when copies of a gene are dispersed rather than repeated tandemly. The presence of intragenomic variability also renders the use of rDNA sequences for barcoding microsporidia questionable. Evidence of recombination in the single-copy genes of putatively asexual microsporidia suggests that these species may undergo cryptic sexual reproduction, a possibility with profound implications for the evolution of virulence, host range and drug resistance in these species

Embedded dielectric microstructures in molecular beam epitaxy : high-quality planar coalescence toward enhanced optoelectronic materials

Seamless integration of embedded dielectric microstructures in III-V crystal growth is a continued area of research due to its numerous high-impact applications. Historically, investigations into embedded dielectric microstructures within existing crystal growth techniques were focused on blocking dislocations at the III-V/dielectric interface in the production of low defect relaxed high mismatched heteroepitaxy. However, recent efforts have broadened the use of embedded dielectric microstructures for enhancement of optoelectronic device functionality and development of monolithic growth schemes toward integrated photonic circuits. The central challenge of embedding dielectric microstructures in III-V materials is achieving single-crystal high-quality planar coalescence within existing conventional III-V crystal growth techniques without defect. While prevalent in the field of III-V crystal growth, solid-source Molecular Beam Epitaxy (MBE) has a well-known "coalescence problem," historically lacking approaches that achieve planar coalescence over dielectric microstructures. Limited coalescence is in large part due to low diffusion of III-adatoms on dielectric surfaces, typically below 300nm, readily forming polycrystalline deposition on dielectric surfaces exceeding this diffusion length. Several solid-source MBE highly-selective growth and lateral epitaxial overgrowth (LEO) growth approaches have been reported; however, none demonstrating complete planar coalescence over dielectric microstructures. In this dissertation, to overcome the "coalescence problem," we demonstrate for the first time a general methodology for an all-MBE growth of high-quality planar coalescence over a variety of embedded dielectric microstructures. Underpinning the approach, we developed a two-stage all-MBE growth approach for GaAs and InAs on (001) substrates, producing highly selective LEO and planarization, returning the growth front to the (001) surface. Characterization of the growth approach demonstrates for the first time an all-MBE approach to planar coalescence. In application of the two-stage all-MBE growth approach towards photonics, we demonstrate enhancement of quantum emitters using buried silica gratings arrays and develop several methodologies for embedded high-contrast photonic materials through self-formed air voids and molded air channel processes. Lastly, in application to high-quality relaxed high mismatch heteroepitaxy, we demonstrate for the first time an all-MBE approach to III-V metamorphic heteroepitaxy, demonstrating threading dislocation reduction in InAs/GaAs metamorphics with high fill factor embedded silica gratings. Thus, from the material presented here, we provide several significant advances to the long-standing challenge of marrying high-quality semiconductor crystal growth with dielectric microstructures, unlocking several high-impact applications, including high-quality material pathways for enhanced quantum emitters and embedded metasurfaces as well as an all-MBE approach toward heterogeneous III-V integration on silicon.Electrical and Computer Engineerin

Microsporidian parasites feminise hosts without paramyxean co-infection:Support for convergent evolution of parasitic feminisation

AbstractFeminisation of amphipod crustaceans is associated with the presence of at least three microsporidian parasites and one paramyxean parasite, suggesting that the ability to feminise has evolved multiple times in parasites of amphipods. Co-infection by a paramyxean with one of the putative microsporidian feminisers, Dictyocoela duebenum, has inspired the alternative hypothesis that all feminisation of amphipods is caused by paramyxea and that all microsporidian associations with feminisation are due to co-infection with paramyxea (Short et al., 2012). In a population of the amphipod Gammarus duebeni, breeding experiments demonstrate that the microsporidia D. duebenum and Nosema granulosis are associated with feminisation in the absence of paramyxea. Co-infection of the two microsporidia is no more frequent than expected at random and each parasite is associated with feminisation in the absence of the other. These findings support the original hypothesis that the ability to feminise amphipods has evolved in microsporidia on multiple occasions. Additionally, the occurrence of a non-feminising strain of D. duebenum in Gammarus pulex suggests that different strains vary in their feminising ability, even within microsporidian species. The presence or absence of feminising ability in a particular microsporidian strain should not therefore be generalised to the species as a whole

Population genetic structure of the European lobster (Homarus gammarus) in the Irish Sea and implications for the effectiveness of the first British marine protected area

Levels of self-recruitment within and connectivity among populations are key factors influencing marine population persistence and stock sustainability, as well as the effectiveness of spatially explicit management strategies such as Marine Protected Areas (MPAs). In the United Kingdom (UK), Lundy Island in the Bristol Channel was designated a No-Take Zone (NTZ) in 2003 and became the UK’s first Marine Conservation Zone (MCZ) in 2009. This NTZ is expected to represent an additional resource for the sustainable management of the European lobster (Homarus gammarus) fishery. As the first step in a genetic monitoring program, this study aimed to investigate population genetic structure of lobster within and between the Irish Sea and Bristol Channel and in doing so to assess the functioning of the Lundy NTZ in the context of connectivity and other genetic parameters. Analysis of microsatellite data indicated that lobsters within the study area are genetically homogeneous and supports the view of a single panmictic population wherein the Lundy NTZ is highly connected. Levels of genetic variability were universally high with no evidence of differences for the NTZ. Furthermore, there was no evidence of recent genetic bottlenecks, and estimates of effective population sizes were infinitely large. The results suggest that if current management and breeding stock sizes are maintained genetic drift will not be strong enough to reduce neutral genetic diversity

Should sex ratio distorting parasites abandon horizontal transmission?

BACKGROUND: Sex-ratio distorting parasites are of interest due to their effects upon host population dynamics and their potential to influence the evolution of host sex determination systems. In theory, the ability to distort host sex-ratios allows a parasite with efficient vertical (hereditary) transmission to dispense completely with horizontal (infectious) transmission. However, recent empirical studies indicate that some sex-ratio distorting parasites have retained the capability for horizontal transmission. RESULTS: Numerical simulations using biologically realistic parameters suggest that a feminising parasite is only likely to lose the capability for horizontal transmission if its host occurs at low density and/or has a male-biased primary sex ratio. It is also demonstrated that even a small amount of horizontal transmission can allow multiple feminising parasites to coexist within a single host population. Finally it is shown that, by boosting its host's rate of population growth, a feminising parasite can increase its own horizontal transmission and allow the invasion of other, more virulent parasites. CONCLUSIONS: The prediction that sex-ratio distorting parasites are likely to retain a degree of horizontal transmission has important implications for the epidemiology and host-parasite interactions of these organisms. It may also explain the frequent co-occurrence of several sex-ratio distorting parasite species in nature

From ocean sprawl to blue-green infrastructure:A UK perspective on an issue of global significance

Artificial structures are proliferating in the marine environment, resulting in ‘ocean sprawl’. In light of the potential environmental impacts of this, such as habitat loss and alteration, it is becoming increasingly important to incorporate ecologically-sensitive design into artificial marine structures. The principles of eco-engineering and green infrastructure are embedded in urban planning practice for terrestrial and freshwater development projects. In marine planning, however, eco-engineering of blue-green infrastructure remains an emerging concept. This note provides a UK perspective on the progress towards uptake of eco-engineering approaches for enhancing biodiversity on artificial marine structures. We emphasise that, despite a clear ‘policy pull’ to incorporate biodiversity enhancements in marine structures, a range of proof-of-concept evidence that it is possible to achieve, and strong cross-sectoral stakeholder support, there are still few examples of truly and purposefullydesigned blue-green artificial structures in the UK. We discuss the barriers that remain and propose a strategy towards effective implementation. Our strategy outlines a step-wise approach to: (1) strengthening the evidence base for what enhancements can be achieved in different scenarios; (2) improving clarity on the predicted benefits and associated costs of enhancements; (3) packaging the evidence in a useful form to support planning and decision-making; and (4) encouraging implementation as routine practice. Given that ocean sprawl is a growing problem globally, the perspective presented here provides valuable insight and lessons for other nations at their various states of progress towards this same goal

Genomic Stability of Composite SCCmec ACME and COMER-Like Genetic Elements in Staphylococcus epidermidis Correlates With Rate of Excision

NA is supported by a fellowship of the King Saud University (Riyadh, Saudi Arabia). The authors thank the work of the management team of the ALICE High Performance Computing Facility at the University of Leicester. JDR is supported by the BBSRC grant BB/P504737/1. Data AvailabiliTy Statement The datasets generated for this study can be found in the GenBank (accession numbers SAMN12840193–SAMN12840250).Peer reviewedPublisher PD