Early Vegetation Development on an Exposed Reservoir: Implications for Dam Removal

The 4-year drawdown of Horsetooth Reservoir, Colorado, for dam maintenance, provides a case study analog of vegetation response on sediment that might be exposed from removal of a tall dam. Early vegetation recovery on the exposed reservoir bottom was a combination of (1) vegetation colonization on bare, moist substrates typical of riparian zones and reservoir sediment of shallow dams and (2) a shift in moisture status from mesic to the xeric conditions associated with the pre-impoundment upland position of most of the drawdown zone. Plant communities changed rapidly during the first four years of exposure, but were still substantially different from the background upland plant community. Predictions from the recruitment box model about the locations of Populus deltoides subsp. monilifera (plains cottonwood) seedlings relative to the water surface were qualitatively confirmed with respect to optimum locations. However, the extreme vertical range of water surface elevations produced cottonwood seed regeneration well outside the predicted limits of drawdown rate and height above late summer stage. The establishment and survival of cottonwood at high elevations and the differences between the upland plant community and the community that had developed after four years of exposure suggest that vegetation recovery following tall dam removal will follow a trajectory very different from a simple reversal of the response to dam construction, involving not only long time scales of establishment and growth of upland vegetation, but also possibly decades of persistence of legacy vegetation established during the reservoir to upland transition

Consequences of Eukaryotic Enhancer Architecture for Gene Expression Dynamics, Development, and Fitness

The regulatory logic of time- and tissue-specific gene expression has mostly been dissected in the context of the smallest DNA fragments that, when isolated, recapitulate native expression in reporter assays. It is not known if the genomic sequences surrounding such fragments, often evolutionarily conserved, have any biological function or not. Using an enhancer of the even-skipped gene of Drosophila as a model, we investigate the functional significance of the genomic sequences surrounding empirically identified enhancers. A 480 bp long “minimal stripe element” is able to drive even-skipped expression in the second of seven stripes but is embedded in a larger region of 800 bp containing evolutionarily conserved binding sites for required transcription factors. To assess the overall fitness contribution made by these binding sites in the native genomic context, we employed a gene-replacement strategy in which whole-locus transgenes, capable of rescuing even-skipped- lethality to adulthood, were substituted for the native gene. The molecular phenotypes were characterized by tagging Even-skipped with a fluorescent protein and monitoring gene expression dynamics in living embryos. We used recombineering to excise the sequences surrounding the minimal enhancer and site-specific transgenesis to create co-isogenic strains differing only in their stripe 2 sequences. Remarkably, the flanking sequences were dispensable for viability, proving the sufficiency of the minimal element for biological function under normal conditions. These sequences are required for robustness to genetic and environmental perturbation instead. The mutant enhancers had measurable sex- and dose-dependent effects on viability. At the molecular level, the mutants showed a destabilization of stripe placement and improper activation of downstream genes. Finally, we demonstrate through live measurements that the peripheral sequences are required for temperature compensation. These results imply that seemingly redundant regulatory sequences beyond the minimal enhancer are necessary for robust gene expression and that “robustness” itself must be an evolved characteristic of the wild-type enhancer

Tempo and Mode in Evolution of Transcriptional Regulation

Perennial questions of evolutionary biology can be applied to gene regulatory systems using the abundance of experimental data addressing gene regulation in a comparative context. What is the tempo (frequency, rate) and mode (way, mechanism) of transcriptional regulatory evolution? Here we synthesize the results of 230 experiments performed on insects and nematodes in which regulatory DNA from one species was used to drive gene expression in another species. General principles of regulatory evolution emerge. Gene regulatory evolution is widespread and accumulates with genetic divergence in both insects and nematodes. Divergence in cis is more common than divergence in trans. Coevolution between cis and trans shows a particular increase over greater evolutionary timespans, especially in sex-specific gene regulation. Despite these generalities, the evolution of gene regulation is gene- and taxon-specific. The congruence of these conclusions with evidence from other types of experiments suggests that general principles are discoverable, and a unified view of the tempo and mode of regulatory evolution may be achievable

Effect of remote ischaemic conditioning on clinical outcomes in patients with acute myocardial infarction (CONDI-2/ERIC-PPCI): a single-blind randomised controlled trial.

BACKGROUND: Remote ischaemic conditioning with transient ischaemia and reperfusion applied to the arm has been shown to reduce myocardial infarct size in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI). We investigated whether remote ischaemic conditioning could reduce the incidence of cardiac death and hospitalisation for heart failure at 12 months. METHODS: We did an international investigator-initiated, prospective, single-blind, randomised controlled trial (CONDI-2/ERIC-PPCI) at 33 centres across the UK, Denmark, Spain, and Serbia. Patients (age >18 years) with suspected STEMI and who were eligible for PPCI were randomly allocated (1:1, stratified by centre with a permuted block method) to receive standard treatment (including a sham simulated remote ischaemic conditioning intervention at UK sites only) or remote ischaemic conditioning treatment (intermittent ischaemia and reperfusion applied to the arm through four cycles of 5-min inflation and 5-min deflation of an automated cuff device) before PPCI. Investigators responsible for data collection and outcome assessment were masked to treatment allocation. The primary combined endpoint was cardiac death or hospitalisation for heart failure at 12 months in the intention-to-treat population. This trial is registered with ClinicalTrials.gov (NCT02342522) and is completed. FINDINGS: Between Nov 6, 2013, and March 31, 2018, 5401 patients were randomly allocated to either the control group (n=2701) or the remote ischaemic conditioning group (n=2700). After exclusion of patients upon hospital arrival or loss to follow-up, 2569 patients in the control group and 2546 in the intervention group were included in the intention-to-treat analysis. At 12 months post-PPCI, the Kaplan-Meier-estimated frequencies of cardiac death or hospitalisation for heart failure (the primary endpoint) were 220 (8·6%) patients in the control group and 239 (9·4%) in the remote ischaemic conditioning group (hazard ratio 1·10 [95% CI 0·91-1·32], p=0·32 for intervention versus control). No important unexpected adverse events or side effects of remote ischaemic conditioning were observed. INTERPRETATION: Remote ischaemic conditioning does not improve clinical outcomes (cardiac death or hospitalisation for heart failure) at 12 months in patients with STEMI undergoing PPCI. FUNDING: British Heart Foundation, University College London Hospitals/University College London Biomedical Research Centre, Danish Innovation Foundation, Novo Nordisk Foundation, TrygFonden

Gregor McGregor

"42902 Cpl Gregor McGregor 76 Fighter Squadron Strauss Field Oct 4[obscured]- Dec. Truscott's Mob. No 5 Rep Centre Tindal. Jan - May 4[obscured]".42902 Corporal Gregor McGregor. 76 Fighter Squadron, Strauss Field. October 4[obscured]- December. Truscott's Mob. Number 5 Repair Centre Tindal. January - May 4[obscured]

Proximate Mechanisms of Task Allocation in Ants

Ants have established themselves as an ecologically dominant organism. One of the critical factors for this ecological success is division of labour whereby work is organised into discrete tasks performed by separate individuals. In this thesis, we focus on worker division of labour, where the allocation of workers to task is roughly correlated with age as young individuals nurse and old individuals forage. However, progression from nurse to forager is considerably more labile than previously thought and researchers have observed precocious foraging and behavioural reversion. Subsequently, in Chapter 1, we explored the relationship between age and task in the ant Camponotus fellah. Using automated ant tracking systems, we follow >500 age-marked workers over three months and used the records of their antennal interactions to construct social networks and evaluate each workers’ social maturity. Analysis of these networks revealed that the timing of the transition from nurse to forager does not correlate with the age of the workers, which is further evidence that whilst age-based polyethism broadly describes division of labour, it cannot explain it. A number of alternative proximate mechanisms have been proposed to explain division of labour, one of which is fat content. Across the eusocial Hymenoptera, there is a correlation between fat content and task, with nurses being fat and foragers lean. In Chapter 2, we established a novel method of fat measurement using Nuclear Magnetic Resonance (NMR) that allowed us for the first time to obtain accurate, quantifiable records of lipid content from living workers, so that changes in fat content could be tracked over time. We then used this development, in combination with starvation of targeted workers, to establish a causal relationship between fat content and division of labour in the ant Myrmica rubra. Starvation induced lower fat content and subsequently those workers had higher social maturity (i.e., forager-like), spent less time on the brood pile, and more time foraging. In Chapter 3, we continue to explore physiological influences on behaviour, this time evaluating the role of the oxytocin/vasopressin-like peptide, inotocin. We showed that the expression of inotocin and its receptor are correlated with task in C. fellah and are upregulated when workers transition from nursing to foraging. By targeting inotocin receptor using dsRNA injection, in combination with pharmaceutical blockers of the inotocin signalling pathway, we reveal that inotocin regulates the synthesis of cuticular hydrocarbons via cytochrome P450. This pathway is likely activated to protect workers from desiccation whilst foraging and suggests that inotocin may influence the timing of nurse to forager transition. Finally, in Chapter 4, we focused on which factors regulate the performance of just a single task, brood transport, in the ant C. floridanus. To manipulate brood transport so that we could reliably study this behaviour, we designed the Ant Nest Temperature Controller system (ANT°C) to manipulate and control nest surface temperature gradients, allowing us to predictably stimulate brood transport behaviour on demand. We established that the workers which performed brood transport were highly specialised, and usually minor, nurse workers. However, the degree of specialisation did not affect the efficiency with which brood transport was performed. Moreover, we were surprised to discover that the subsequent removal of these specialised brood transporters knocked out brood transport behaviour. This suggests that the remaining workers were unable to flexibly reallocate their own tasks to compensate, counter to the prevailing view of division of labour as a highly flexible system. In summary, this thesis further explores the phenomenon of division of labour and the proximate mechanisms and factors that influence task allocation across a variety of ant species. -- Les fourmis se sont imposées comme un organisme écologiquement dominant. Dans cette thèse, nous nous concentrons sur la division du travail des ouvrières, où leur affectation à une tâche est approximativement corrélée à l'âge avec les jeunes qui s’occupent de la reine et du couvain alors que les plus âgées partent à la recherche de nourriture. Cependant, la transition de nourrice à fourragère est considérablement plus labile qu'on ne le pensait auparavant et les chercheurs ont observé de jeunes ouvrières partant précocement à la recherche de la nourriture ou une réversion comportementale avec les fourragères retournant s’occuper du couvain. Pour clarifier cela, dans le premier chapitre, nous avons utilisé un système de suivi automatique par caméra vidéo pour suivre la vie de plus de 500 fourmis (Camponotus fellah) d’âge connu pendant trois mois, afin de calculer précisément l'influence de leur âge sur les tâches qu'elles effectuent. Les enregistrements de leurs interactions antennaires nous ont permis de construire des réseaux sociaux ainsi que d’évaluer la maturité sociale de chaque ouvrière. L'analyse de ces réseaux a révélé que le moment de la transition de nourrice à fourragère n'était pas corrélé à l'âge des ouvrières, ce qui est une preuve supplémentaire que bien que le polyéthisme basé sur l'âge décrit la division du travail de manière générale, il ne peut pas l'expliquer. Un certain nombre de mécanismes proximaux alternatifs ont été proposés pour expliquer la division du travail, dont l'un est la teneur en matières grasses. Chez les hyménoptères eusociaux, il existe une corrélation entre la teneur en graisse et la tâche, les nourrices étant corpulentes et les fourragères maigres. Dans le second chapitre, nous avons mis au point une nouvelle méthode de mesure des graisses grâce à la résonance magnétique nucléaire (RMN). L’avantage de cette méthode est qu’elle nous a permis, pour la première fois, d'obtenir des données précises et quantifiables de la teneur en lipides sur des ouvrières vivantes et de répéter ces mesures sur ces mêmes individus afin d’évaluer les changements de teneur en graisses au cours du temps. En affamant une partie des ouvrières, nous avons pu établir une relation de cause à effet entre la teneur en graisse et la division du travail chez la fourmi Myrmica rubra, les ouvrières affamées ayant rapidement changé de comportement en passant de nourrice à fourragère. En effet, la famine a induit une perte de matière grasse, une augmentation du score de maturité sociale (c.-à-d. comportement semblable aux fourragères), une diminution du temps passé sur le couvain et une augmentation du temps passé à la recherche de nourriture. Dans le troisième chapitre, nous avons continué à explorer les influences physiologiques sur le comportement, cette fois en évaluant le rôle de l’inotocine, un peptide de type ocytocine/vasopressine. Nous avons montré que l'expression de l'inotocine et de son récepteur sont corrélés à la tâche chez C. fellah et sont régulés à la hausse lorsque les ouvrières passent de nourrice à fourragère. En ciblant le récepteur de l'inotocine par l’injection d'ARNdb, en combinaison avec des bloqueurs pharmaceutiques de la voie de signalisation de l'inotocine, nous avons trouvé que l'inotocine régule la synthèse des hydrocarbures cuticulaires via le cytochrome P450. Cette voie est probablement activée pour protéger les travailleurs de la dessiccation lors de la recherche de nourriture et suggère que l'inotocine peut influencer le moment de la transition entre nourrice et fourragère. Finalement dans le chapitre 4, nous nous sommes concentrés sur les facteurs qui régulent la réalisation d'une tâche, le transport du couvain, chez la fourmi C. floridanus. Pour pouvoir étudier ce comportement de manière fiable, nous avons conçu et développé une technologie, le « Ant Nest Temperature Controller » (ANT°C), pour créer et contrôler des gradients de température à la surface du nid. Ceci nous a permis de stimuler de manière prévisible, et sur demande, le comportement de transport du couvain. Nous avons pu établir que les ouvrières transportant le couvain étaient des nourrices hautement spécialisées et généralement de petites tailles. Par ailleurs, le degré de spécialisation n'a pas affecté l'efficacité avec laquelle le transport du couvain a été effectué. Finalement, nous avons été surpris de découvrir que le retrait des transporteuses de couvain a eu comme conséquence de stopper entièrement le transport du couvain dans la colonie. Ceci suggère que les ouvrières restantes étaient incapables de réaffecter leurs tâches de manière flexible pour compenser la disparition des transporteuses de couvain, contrairement à l'opinion majoritaire selon laquelle la division du travail est un système hautement flexible. En résumé, cette thèse explore plus en détail le phénomène de division du travail, ainsi que les mécanismes proximaux et facteurs influençant la répartition des tâches chez plusieurs espèces de fourmis

Shape and function of the Bicoid morphogen gradient in dipteran species with different sized embryos

AbstractThe Bicoid morphogen evolved approximately 150 MYA from a Hox3 duplication and is only found in higher dipterans. A major difference between dipteran species, however, is the size of the embryo, which varies up to 5-fold. Although the expression of developmental factors scale with egg length, it remains unknown how this scaling is achieved. To test whether scaling is accounted for by the properties of Bicoid, we expressed eGFP fused to the coding region of bicoid from three dipteran species in transgenic Drosophila embryos using the Drosophila bicoid cis-regulatory and mRNA localization sequences. In such embryos, we find that Lucilia sericata and Calliphora vicina Bicoid produce gradients very similar to the endogenous Drosophila gradient and much shorter than what they would have produced in their own respective species. The common shape of the Drosophila, Lucilia and Calliphora Bicoid gradients appears to be a conserved feature of the Bicoid protein. Surprisingly, despite their similar distributions, we find that Bicoid from Lucilia and Calliphora do not rescue Drosophila bicoid mutants, suggesting that that Bicoid proteins have evolved species-specific functional amino acid differences. We also found that maternal expression and anteriorly localization of proteins other than Bcd does not necessarily give rise to a gradient; eGFP produced a uniform protein distribution. However, a shallow gradient was observed using eGFP-NLS, suggesting nuclear localization may be necessary but not sufficient for gradient formation