Host-hijacking and planktonic piracy: how phages command the microbial high seas

Microbial communities living in the oceans are major drivers of global biogeochemical cycles. With nutrients limited across vast swathes of the ocean, marine microbes eke out a living under constant assault from predatory viruses. Viral concentrations exceed those of their bacterial prey by an order of magnitude in surface water, making these obligate parasites the most abundant biological entities in the ocean. Like the pirates of the 17th and 18th centuries that hounded ships plying major trade and exploration routes, viruses have evolved mechanisms to hijack microbial cells and repurpose their cargo and indeed the vessels themselves to maximise viral propagation. Phenotypic reconfiguration of the host is often achieved through Auxiliary Metabolic Genes – genes originally derived from host genomes but maintained and adapted in viral genomes to redirect energy and substrates towards viral synthesis. In this review, we critically evaluate the literature describing the mechanisms used by bacteriophages to reconfigure host metabolism and to plunder intracellular resources to optimise viral production. We also highlight the mechanisms used when, in challenging environments, a ‘batten down the hatches’ strategy supersedes that of ‘plunder and pillage’. Here, the infecting virus increases host fitness through phenotypic augmentation in order to ride out the metaphorical storm, with a concomitant impact on host substrate uptake and metabolism, and ultimately, their interactions with their wider microbial community. Thus, the traditional view of the virus-host relationship as predator and prey does not fully characterise the variety or significance of the interactions observed. Recent advances in viral metagenomics have provided a tantalising glimpse of novel mechanisms of viral metabolic reprogramming in global oceans. Incorporation of these new findings into global biogeochemical models requires experimental evidence from model systems and major improvements in our ability to accurately predict protein function from sequence data

Biogeography of a Plant Invasion: Plant–Herbivore Interactions

Theory predicts that native plant species should exhibit latitudinal gradients in the strength of their interactions with herbivores. We hypothesize that if an invasive plant species exhibits a different latitudinal gradient in response to herbivores (e.g., a nonparallel gradient), it can create large-scale heterogeneities in community resistance/susceptibility to the invasive species. We conducted a study of latitudinal variation in the strength of herbivory and defenses of native genotypes of Phragmites australis in North America (NA) and Europe (EU) and European invasive genotypes in NA. Within NA, we tested whether (1) invasive genotypes are better defended and suffer less herbivory than co-occurring native genotypes, (2) herbivory and defenses of native P. australis decreases with increasing latitude; and (3) invasive genotypes exhibit either no latitudinal gradient, or a nonparallel latitudinal gradient in herbivory and defenses compared to native genotypes. For the European genotypes, we tested two additional hypotheses: (4) defenses, nutritional condition, and herbivory would differ between the native (EU) and invasive ranges (NA) and (5) latitudinal gradients in defenses and herbivory would be similar between ranges. Within NA, chewing damage, internal stem-feeding incidence, and aphid abundance were 650%, 300%, and 70% lower, respectively, on invasive than native P. australis genotypes. Genotypes in NA also differed in nutritional condition (percent N, C:N ratio), but there was little support for invasive genotypes being better defended than native genotypes. For the European genotypes, herbivory was significantly lower in the invaded than native range, supporting the enemy-release hypothesis. Defense levels (leaf toughness and total phenolics) and tissue percent C and percent N were higher in the invaded than native range for European genotypes. Overall, latitudinal gradients in P. australis nutritional condition, defenses, and herbivory were common. Interestingly, chewing damage and stem-feeder incidence decreased with latitude for native P. australis genotypes in NA and EU, but no latitudinal gradients in response to herbivores were evident for invasive genotypes in NA. Nonparallel latitudinal gradients in herbivory between invasive and native P. australis suggest that the community may be more susceptible to invasion at lower than at higher latitudes. Our study points to the need for invasion biology to include a biogeographic perspective

Biological control of invasive Phragmites australis will be detrimental to native P. australis

Phragmites australis biological control is intended to address a major invasion in North America and is likely to change the ecology of vast areas of coastal and inland wetlands. However, the real risks to the native North American genotypes of P. australis (as indicated by recent research summarized above) may not have been fully considered, particularly the extirpation of native populations or the eventual extinction of the native North American lineage altogether. The concerns we raise need to be considered in the process of developing and approving the release of biological control agents and the entire approval process would benefit from greater transparency and wider input from Phragmites researchers globally

Response to Blossey and Casagrande: ecological and evolutionary processes make host specificity at the subspecies level exceedingly unlikely

We agree with Blossey and Casagrande (2016) that absolute host-specificity is a necessity for successful biological control of invasive plants without unintended consequences for native species. However, inclusion of non-target native species in the diet of a biological control agent is a relatively common phenomenon with native congeners of the target plant species at greatest risk (Pemberton 2000)

Biogeography of a plant invasion: drivers of latitudinal variation in enemy release

© 2016 John Wiley & Sons Ltd Aim: The relationship between herbivory and latitude may differ between native and invasive plant taxa, which can generate biogeographical heterogeneity in the strength of enemy release. Our aim was to compare latitudinal gradients in herbivory between native and invasive plants and investigate whether gradients are driven by local adaptation or phenotypic plasticity. Location: North America. Methods: Using sympatric native and invasive lineages of the wetland grass Phragmites australis and the specialist gall-fly Lipara rufitarsis, we conducted a field survey to examine whether the relationship between herbivory (the proportion of stems galled) and latitude was parallel between lineages. In a subsequent common garden experiment, we assessed whether latitudinal gradients in herbivory were genetically based or driven by phenotypic plasticity. Results: In the field, L. rufitarsis herbivory on the native P. australis lineage increased from 27% of stems galled in southern populations (36.5°) to 37% in northern populations (43.6°), whereas there was no relationship for the invasive lineage. Similar relationships were evident in the common garden experiment, indicating a genetic basis to latitudinal variation in herbivory. Moreover, the invasive lineage suffered five times less herbivory than the native lineage on average, supporting the enemy release hypothesis. However, a genetic basis to this pattern was absent in the common garden experiment, suggesting that local environmental conditions were responsible for the enemy release observed in nature. Specifically, stem height, diameter and density during the L. rufitarsis oviposition period appeared to be important drivers of herbivory. Main conclusions: Non-parallel gradients in herbivory may help explain the equivocal results of other studies that examine enemy release and biotic resistance at local scales, and can be an important mechanism promoting biogeographical variation in invasion success. We suggest that these latitudinal patterns in herbivory and other species interactions are likely to be a common phenomenon across a range of invaded systems

The 2-10 keV XRB dipole and its cosmological implications

The hard X-ray (>2 keV) emission of the local and distant Universe as observed with the HEAO1-A2 experiment is reconsidered in the context of large scale cosmic structure. Using all-sky X-ray samples of AGN and galaxy clusters we remove the dominant local X-ray flux from within a redshift of ~ 0.02. We evaluate the dipolar and higher order harmonic structure in 4 X-ray colours. The estimated dipole anisotropy of the unresolved flux appears to be consistent with a combination of the Compton-Getting effect due to the Local Group motion (dipole amplitude Delta = 0.0042) and remaining large scale structure (0.0023 <~ Delta <~ 0.0085), in good agreement with the expectations of Cold Dark Matter models. The observed anisotropy does however also suggest a non-negligible Galactic contribution which is more complex than current, simple models of >2 keV Galactic X-ray emission. Comparison of the soft and hard colour maps with a harmonic analysis of the 1.5 keV ROSAT all-sky data qualitatively suggests that at least a third of the faint, unresolved ~ 18 deg scale structure in the HEAO1-A2 data may be Galactic in origin. However, the effect on measured flux dipoles is small (<~3%). We derive an expression for dipole anisotropy and acceleration and demonstrate how the dipole anisotropy of the distant X-ray frame can constrain the amplitude of bulk motions of the universe. From observed bulk motions over a local ~ 50 Mpc/h radius volume we determine 0.14 <~ Omega^0.6/b_x(0) <~ 0.59.Comment: 39 pages, Revised version accepted ApJ Main Journal, 3 new Figures + additional tex

Intraspecific and biogeographical variation in foliar fungal communities and pathogen damage of native and invasive Phragmites australis

AimRecent research has highlighted that the relationship between species interactions and latitude can differ between native and invasive plant taxa, generating biogeographical heterogeneity in community resistance to plant invasions. In the first study with foliar pathogens, we tested whether co‐occurring native and invasive lineages of common reed (Phragmites australis) exhibit non‐parallel latitudinal gradients in foliar fungal communities, pathogen susceptibility and damage, and whether these biogeographical patterns can influence the success of invasion.LocationNorth America.Time period2015–2017.Major taxa studiedPerennial grass P. australis.MethodsWe surveyed 35 P. australis field populations, spanning 17° latitude and comprising four phylogeographical lineages, including one endemic to North America and one invasive from Europe. For each population, we quantified the percentage of leaf pathogen damage and cultured fungi from diseased leaves, which we identified using molecular tools. To assess whether latitudinal gradients in pathogen damage had a genetic basis, we inoculated plants from 73 populations with four putative pathogens in a complementary common garden experiment and measured P. australis susceptibility (i.e., diseased leaf area).ResultsWe isolated 84 foliar fungal taxa. Phragmites australis lineage influenced fungal community composition but not diversity. Despite the invasive European P. australis lineage being the least susceptible to three of the four pathogens tested in the common garden experiment, pathogen damage in the field was similar between native and invasive lineages, providing no evidence that release from foliar pathogens contributes to the success of invasion. Genetically based latitudinal gradients in pathogen susceptibility observed in the common garden were isolate specific and obscured by local environmental conditions in the field, where pathogen damage was threefold higher for northern compared with southern populations, regardless of lineage.Main conclusionsOur results highlight that host plant lineage and genetically based biogeographical gradients strongly influence foliar fungal communities and pathogen susceptibility, but do not translate to patterns of pathogen damage observed in the field.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155999/1/geb13097.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155999/2/geb13097_am.pd

Nitrogen Fixation and Seeding Rates of Common vs. Hairy Vetch for Interseeding Into Established Switchgrass Stands

Interest in alternatives to synthetic nitrogen (N) fertilizer sources for switchgrass (Panicum virgatum L.) production, such as interseeding with N- fixing legumes continues to increase. Common vetch (Vicia sativa) is a N-fixing legume that occurs naturally throughout the U.S. and has less hard seed than hairy vetch (Vicia villosa), making it potentially less invasive, and it may fix N at similar rates to that of hairy vetch. However, little data exist to substantiate this. In this study, N-fixation rates via the N-difference method were determined to be 59.3 and 43.3 kg N ha-1 for common and hairy vetch, respectively, when seeded at 6.7 kg ha-1. At these rates, neither common nor hairy vetch significantly affected switchgrass yields. Based on the N-fixation rates and vetch plant masses, we estimate that minimum seeding rates of 7.6 and 10.4 kg PLS ha-1 of common and hairy vetch, respectively are required to obtain plant stands needed to fix the current recommended rate of N for switchgrass biomass production