Factors influencing the publication of health research

Objectives: Assess the degree to which research project findings were published and explore factors that influenced publication. Methods: Questionnaire to project leaders. Classification of publications and findings. Chi-squared; univariate and multivariate Cox regression analyses. Results: Forty percent of projects published in peer-reviewed journal; highly statistically significant relationships between publication in peer-reviewed journals and (1) projects in Responsive/Fellowships streams (p = .045); and (2) projects awarded >pound22,713 (p = .02); influence of study findings not statistically significant. Conclusions: Funders should consider the significant number of studies that did not result in publication and the higher rate of publication in peer-reviewed journals from some programs

Autonomous model protocell division driven by molecular replication

The coupling of compartmentalisation with molecular replication is thought to be crucial for the emergence of the first evolvable chemical systems. Minimal artificial replicators have been designed based on molecular recognition, inspired by the template copying of DNA, but none yet have been coupled to compartmentalisation. Here, we present an oil-in-water droplet system comprising an amphiphilic imine dissolved in chloroform that catalyses its own formation by bringing together a hydrophilic and a hydrophobic precursor, which leads to repeated droplet division. We demonstrate that the presence of the amphiphilic replicator, by lowering the interfacial tension between droplets of the reaction mixture and the aqueous phase, causes them to divide. Periodic sampling by a droplet-robot demonstrates that the extent of fission is increased as the reaction progresses, producing more compartments with increased self-replication. This bridges a divide, showing how replication at the molecular level can be used to drive macroscale droplet fission

Canard-like phenomena in piecewise-smooth Van der Pol systems

We show that a nonlinear, piecewise-smooth, planar dynamical system can exhibit canard phenomena. Canard solutions and explosion in nonlinear, piecewise-smooth systems can be qualitatively more similar to the phenomena in smooth systems than piecewise-linear systems, since the nonlinearity allows for canards to transition from small cycles to canards ``with heads." The canards are born of a bifurcation that occurs as the slow-nullcline coincides with the splitting manifold. However, there are conditions under which this bifurcation leads to a phenomenon called super-explosion, the instantaneous transition from a globally attracting periodic orbit to relaxations oscillations. Also, we demonstrate that the bifurcation---whether leading to canards or super-explosion---can be subcritical.Comment: 17 pages, 11 figure

Shared parasitoids in a metacommunity: Indirect interactions inhibit herbivore membership in local communities

The interaction between species, mediated by a shared natural enemy (i.e., apparent competition), has been the subject of much theoretical and empirical investigation. However, we lack field experiments that assess the importance of apparent competition to metacommunity structure. Here, I conducted a series of field experiments to test whether apparent competition, mediated by shared egg parasitoids (Anagrus nigriventris and A. columbi), occurs between two abundant planthopper species (Delphacodes scolochloa and Prokelisia crocea) of the North American Great Plains. The two planthoppers feed on different plant species within prairie potholes (wet depressions) and, thus, do not interact directly. At the scale of individual potholes, a five-fold pulse increase in D. scolochloa density (relative to control potholes) resulted in a steady decline in P. crocea density over two generations. As expected in cases of apparent competition, P. crocea eggs in these potholes suffered twice the level of parasitism as P. crocea eggs in control potholes. In contrast, a sixfold increase in P. crocea density had no effect on D. scolochloa density or parasitism in those potholes. The superiority of D. scolochloa over P. crocea likely can be attributed to a larger source population size, greater amount of host habitat, and/or the presence of a phenological refuge from parasitism for D. scolochloa. In another experiment, in which small populations of P. crocea were established either in close proximity to D. scolochloa or in isolation, I found that the likelihood of P. crocea persistence was 36% lower in the former than the latter populations. This difference was attributable to very high rates of parasitism of P. crocea when adjacent to D. scolochloa. These two experiments provide clear evidence that the two planthopper species engage in apparent competition and that the shared parasitoids may play a significant role in limiting membership in a local community. Based on these findings, I argue that metacommunity studies must be broadened to include higher trophic levels. © 2007 by the Ecological Society of America

From population sources to sieves: The matrix alters host-parasitoid source-sink structure

Field experiments that examine the impact of immigration, emigration, or landscape structure (e.g., the composition of the matrix) on the source-sink dynamics of fragmented populations are scarce. Here, planthoppers (Prokelisia crocea) and egg parasitoids (Anagrus columbi) were released among host-plant patches that varied in structural (caged, isolated, or in a network of other patches) and functional (mudflat matrix that impedes dispersal vs. brome-grass matrix that facilitates dispersal) connectivity. Planthoppers and parasitoids on caged patches exhibited density-dependent growth rates, achieved high equilibrium densities, and rarely went extinct. Therefore, experimental cordgrass patches were classified as population sources. Because access to immigrants did not result in elevated population densities, source populations were not also pseudosinks, i.e., patches whose densities occur above carrying capacity due to high immigration. Planthoppers and parasitoids in open patches in mudflat had dynamics similar to those in caged patches, but went extinct in 4-5 generations in open patches in brome. Brome-embedded patches leaked emigrants at a rate that exceeded the gains from reproduction and immigration; populations of this sort are known as population sieves. For species whose suitable patches are becoming smaller and more isolated as a result of increased habitat fragmentation, emigration losses are likely to become paramount, a condition favoring the formation of population sieves. An increase in the proportion of patches that are sieves is predicted to destabilize regional population dynamics. © 2007 by the Ecological Society of America

Matrix heterogeneity and host-parasitoid interactions in space

In this study, I experimentally examined how the landscape matrix influenced the movement, oviposition behavior, and spatial distribution of Anagrus columbi, a common egg parasitoid of the planthopper Prokelisia crocea. Both species exist among discrete patches of prairie cordgrass (Spartina pectinata), the sole host plant of P. crocea. Based on out-planted cordgrass pots bearing host eggs (to assess parasitism) or sticky leaves (traps for adult A. columbi), I found that the distribution of adult female A. columbi and pattern of ovipositions within a cordgrass patch were strongly matrix dependent. Female densities were 59% lower on the edge than interior of patches embedded in a mudflat matrix, but were evenly distributed within patches embedded in a matrix consisting of either native grasses or the exotic grass smooth brome (Bromus inermis). In contrast, parasitism was higher in the interior than edge for patches in all three matrix types. The lack of correspondence between A. columbi density and parasitism was attributed to differences in oviposition behavior: A. columbi parasitized 71% more hosts per capita in the interior than edge for patches embedded in nonhost grasses, but equal numbers on the edge and interior of patches embedded in mudflat. Matrix-dependent differences in the within-patch distribution and oviposition behavior of A. columbi can influence the distribution of parasitism risk and host-parasitoid stability at the patch level. Matrix composition also affected the pattern of movement through the matrix and the colonization of nearby cordgrass patches. Anagrus columbi females emigrating from a mudflat-embedded patch were captured at very low, but constant, numbers with distance out into the matrix, suggesting that they were reluctant to enter or remain in the mudflat. In contrast, A. columbi females entering a nonhost grass matrix had numbers that were high near the patch border and then declined exponentially with distance. These patterns of movement were likely responsible for the very different colonization rates for experimental patches embedded in different matrix types and located 3 m from a source patch of A. columbi. Patches embedded in brome were colonized at a rate that was 3.0 and 5.7 times higher than for patches in native grass or mudflat, respectively. Finally, based on a census of cordgrass patches spanning five generations, A. columbi densities and proportion of patches occupied generally increased with increasing host density, patch isolation, and the proportion of the surrounding matrix that was mudflat. Patch size had no effect on the distribution of A. columbi. Overall, these data suggest that cordgrass patches in a nonhost grass matrix, particularly smooth brome, have high connectivity relative to patches in a mudflat matrix. Changes in connectivity due to changes in matrix composition can significantly influence host-parasitoid persistence at the metapopulation level

Spatial Ecology of the Palm-Leaf Skeletonizer, Homaledra sabelella (Lepidoptera: Coleophoridae)

Understanding the processes that determine the distribution of populations is a fundamental goal in ecology. In this study, I determined the relative contribution of space and the biotic and abiotic environment to the distribution of the palm-leaf skeletonizer Homaledra sabalella (PLS; Lepidoptera: Coleophoridae) among patchily distributed dwarf palmettos (Sabal minor; Arecaceae). Based on surveys conducted at two sites in the Sherburne Wildlife Management Area, Louisiana, I found that the distribution of the PLS was primarily related to local environmental conditions – number of PLS increased with palmetto height, was greater in dry versus wet habitats, and varied in an inconsistent way with the type of understory cover. Spatial structure of the forest and isolation of the host plant were of minor importance to the distribution of the PLS. Based on a series of experiments, the mechanisms underlying the effects of these environmental variables on PLS abundance were elucidated. Tall palmettos have a greater abundance of PLS because they are 2.5 times more likely to be colonized than small palmettos. Tall palmettos do not represent better hosts (in terms of PLS survival to pupation, pupal length, or risk of parasitism). Similarly, an open understory increased colonization by two-fold, relative to a shrub understory, but understory type had no effect on host quality. Wet soils greatly reduced palmetto quality as a host (survival and pupal length), but only for the smallest palmettos (<0.75 m height). Finally, corroborating the survey data, my dispersal experiment revealed that the PLS is a strong flier and that local PLS populations (i.e., infested palmettos) are likely well connected by dispersal. I conclude by discussing how landscape-level changes at Sherburne Wildlife Management Area, owing to recent hurricane activity, could affect the risk of palmetto infestation by the PLS

Exploding lakes in Vanuatu - "Surtseyan-style" eruptions witnessed on Ambae Island

After a long silence, Lake Vui on Ambae Island burst into spectacular life on the 28th of November 2005, disrupting the lives of 10 000 inhabitants on this sleepy tropical island in the SW Pacific. "Surtseyan- style" explosions burst through the Island's summit lake waters forming a new tuff-cone and threatening to form deadly lahars or volcanic floods. Such eruptions are rarely well observed, and these fleeting opportunities provide a chance to match volcanic processes with rock-sequences found commonly in the geologic recor