Light is a primary driver of lake ecosystem metabolism, and the dependence of primary production on light is often quantified as a photosynthesis-irradiance or “P-I” curve. The parameters of the P-I ...curve (e.g., the maximum primary production when light is in excess) can change through time due to a variety of biological factors (e.g., changes in biomass or community composition), which themselves are subject to external drivers (e.g., herbivory or nutrient availability). However, the relative contribution of variation in the P-I curve to overall ecosystem metabolism is largely unknown. I developed a statistical model of ecosystem metabolism with time-varying parameters governing the P-I curve, while also accounting for the influence of temperature. I parameterized the model with dissolved oxygen time series spanning six summers from Lake Mývatn, a shallow eutrophic lake in northern Iceland with large temporal variability in ecosystem metabolism. All of the estimated parameters of the P-I curve varied substantially through time. The sensitivity of primary production to light under light-limiting conditions was particularly variable (> 15-fold) and had a compensatory relationship with ambient light levels. However, the 3.5-fold variation in the maximum potential primary production made the largest contribution to variation in ecosystem metabolism, accounting for around 90% of the variance in net ecosystem production. Much of the variation in maximum primary production was attributable to cyanobacterial blooms, which occur in some but not all years in Mývatn. Overall, these results illustrate how changes in the P-I curve contribute substantially to temporal variation in lake ecosystem metabolism.
It has been generally accepted that biosynthesis of protoheme (heme) uses a common set of core metabolic intermediates that includes protoporphyrin. Herein, we show that the Actinobacteria and ...Firmicutes (high-GC and low-GC Gram-positive bacteria) are unable to synthesize protoporphyrin. Instead, they oxidize coproporphyrinogen to coproporphyrin, insert ferrous iron to make Fe-coproporphyrin (coproheme), and then decarboxylate coproheme to generate protoheme. This pathway is specified by three genes named hemY , hemH , and hemQ . The analysis of 982 representative prokaryotic genomes is consistent with this pathway being the most ancient heme synthesis pathway in the Eubacteria. Our results identifying a previously unknown branch of tetrapyrrole synthesis support a significant shift from current models for the evolution of bacterial heme and chlorophyll synthesis. Because some organisms that possess this coproporphyrin-dependent branch are major causes of human disease, HemQ is a novel pharmacological target of significant therapeutic relevance, particularly given high rates of antimicrobial resistance among these pathogens.
Significance It has been accepted dogma that eukaryotes and heme-synthesizing bacteria use the same metabolic intermediates in their heme synthesis pathways, where protoporphyrin is the final intermediate into which iron is inserted to make protoheme. Herein, we present data demonstrating that Gram-positive bacteria do not use protoporphyrin as an intermediate but, instead, have an altered set of terminal reactions that oxidize coproporphyrinogen to coproporphyrin and insert ferrous iron into coproporphyrin, resulting in the formation of coproheme. A newly characterized enzyme, HemQ, decarboxylates coproheme to generate protoheme. Because some organisms that possess this coproporphyrin-dependent branch are major causes of human disease, HemQ is a novel pharmacological target of significant therapeutic relevance, particularly given high rates of antimicrobial resistance among these pathogens.
Uncovering the demographic basis of population fluctuations is a central goal of population biology. This is particularly challenging for spatially structured populations, which require disentangling ...synchrony in demographic rates from coupling via movement between locations. In this study, we fit a stage-structured metapopulation model to a 29-year time series of threespine stickleback abundance in the heterogeneous and productive Lake Mývatn, Iceland. The lake comprises two basins (North and South) connected by a channel through which the stickleback disperse. The model includes time-varying demographic rates, allowing us to assess the potential contributions of recruitment and survival, spatial coupling via movement, and demographic transience to the population’s large fluctuations in abundance. Our analyses indicate that recruitment was only modestly synchronized between the two basins, whereas survival probabilities of adults were more strongly synchronized, contributing to cyclic fluctuations in the lake-wide population size with a period of approximately 6 years. The analyses further show that the two basins were coupled through movement, with the North Basin subsidizing the South Basin and playing a dominant role in driving the lake-wide dynamics. Our results show that cyclic fluctuations of a metapopulation can be explained in terms of the combined effects of synchronized demographic rates and spatial coupling.
Quantifying temporal variation in demographic rates is a central goal of population ecology. In this study, we analyzed a multidecadal age-structured time series of Arctic char (Salvelinus alpinus) ...abundance in Lake Mývatn, Iceland, to infer the time-varying demographic response of the population to reduced harvest in the wake of the fishery’s collapse. Our analysis shows that while survival probability of adults increased following the alleviation of harvesting pressure, per capita recruitment consistently declined over most of the study period, until the final three years when it began to increase. The countervailing demographic trends resulted in only limited directional change in the total population size and population growth rate. Rather, the population dynamics were dominated by large interannual variability and a shift towards an older age distribution. Our results are indicative of a slow recovery of the population after its collapse, despite the rising number of adults following relaxed harvest. This underscores the potential for heterogeneous demographic responses to management efforts due to the complex ecological context in which such efforts take place.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Adaptive genetic divergence occurs when selection imposed by the environment causes the genomic component of the phenotype to differentiate. However, genomic signatures of natural selection are ...usually identified without information on which trait is responding to selection by which selective agent(s). Here, we integrate whole‐genome sequencing with phenomics and measures of putative selective agents to assess the extent of adaptive divergence in threespine stickleback occupying the highly heterogeneous lake Mývatn, NE Iceland. We find negligible genome wide divergence, yet multiple traits (body size, gill raker structure and defence traits) were divergent along known ecological gradients (temperature, predatory bird densities and water depth). SNP based heritability of all measured traits was high (h2 = 0.42–0.65), indicating adaptive potential for all traits. Environment‐association analyses further identified thousands of loci putatively involved in selection, related to genes linked to, for instance, neuron development and protein phosphorylation. Finally, we found that loci linked to water depth were concurrently associated with pelvic spine length variation ‐ supporting the conclusion that divergence in pelvic spine length occurred in the face of gene flow. Our results suggest that whilst there is substantial genetic variation in the traits measured, phenotypic divergence of Mývatn stickleback is mostly weakly associated with environmental gradients, potentially as a result of substantial gene flow. Our study illustrates the value of integrative studies that combine genomic assays of multivariate trait variation with landscape genomics.
Greining merkja um náttúrulegt val í stofni með frjálst genaflæði með greiningu á tengslum erfða, svipgerðar og umhverfis
Erfðafræðilegur aðskilnaður vegna aðlögunar verður þegar umhverfisþættir leiða til valþrýstings sem hefur áhrif á erfðaþætti sem tengjast svipgerðum. Oftast eru merki um náttúrulegt val í erfðamengjum náttúrlegra stofna greind án nákvæmra upplýsinga um það hvaða svipfarseiginleikar eru að bregðast við ólíkum valkröftum. Hér samþættum við gögn úr raðgreiningu á heilum erfðamengjum, svipfarsmælingar og mælingar á umhverfisþáttum sem líklegir eru til að valda valþrýstingi, til þess að leggja mat á aðskilnað vegna aðlagana hjá hornsílum í fjölbreyttum búsvæðum Mývatns. Mjög lítill erfðamismunur fannst milli hópa, þótt ýmis svipgerðareinkenni (stærð, lögun tálknatinda og eiginleikar tengdir vörnum gegn afráni) væru mismunandi þeirra á milli, og sýndu fylgni við ýmsar umhverfisbreytur (hitastig, dýpi og þéttleika fugla sem veiða hornsíli). Arfgengi eiginleika (byggt á stökum basabreytingum sem tengjast mældum eiginleikum) var hátt (h2 = 0.42–0.65), sem bendir til þess að allir þessir eiginleikar geti tengst aðlögun. Greining á tengslum erfðabreytileika og umhverfisþátta vísaði á þúsundir seta sem gætu tengst náttúrulegu vali í genum sem tengjast til dæmis taugaþroskun og fosfórun próteina. Að lokum komumst við að því að set með tengsl við lengd kviðgadds sýndu skýr tengsl við umhverfisþáttinn dýpi, sem styður þá ályktun að þróunarfræðilegur aðskilnaður hafi orðið í lengd kviðgadda þrátt fyrir umtalsvert genaflæði. Niðurstöður okkar benda til þess að þótt mikill erfðabreytileiki sé til staðar tengdur eiginleikunum sem mældir voru sé svipfarsbreytileiki hornsíla í Mývatni í veikum tengslum við umhverfisþætti, líklega vegna mikils genaflæðis. Niðurstöðurnar sýna glöggt mikilvægi samþættra rannsókna þar sem horft er til erfðabreytileika og fjölda svipfarsþátta með notkun landslagserfðamengjafræði.
Plants have evolved both physical and chemical defenses to make the nutrients of attacked organs difficult to access or more toxic to resist animal consumption or/and pathogen attack. Although it is ...intuitive that a tradeoff could exist between physical and chemical defenses because of finite defense resources, many studies have failed to detect this tradeoff. We hypothesized that tradeoff between physical and chemical defenses in individual organs was mediated by the total resource allocation to those organs. In this study, we tested whether a tradeoff between physical (i.e. fiber content, which has proved to be a good indicator of investment into seed coat) and chemical defenses (i.e. total phenolics, which are abundant chemical defenses in plant seeds) existed in plant seeds by using 163 common species collected from Xishuangbanna tropical forest, southwest China. Then we tested whether this tradeoff was mediated by seed mass which could be a potential proxy of total resource investment per seed. Among the 163 species, there was large interspecific variation in both total phenolics (from 0.01 to 20.52%) and fiber content (from 4.47 to 81.49%). Our results supported our hypothesis: negative relationships between physical and chemical defenses were much stronger among small seeds than among large seeds. Our study suggests that total resource acquisition must be considered when evaluating defense tradeoffs. However, it is usually extremely difficult to measure this resource acquisition variation, thus we suggest utilizing easily measured proxies of acquisition variation to quantify tradeoffs.
Abstract
Background
Carbapenem resistance is a critical healthcare challenge worldwide. Particularly concerning is the widespread dissemination of Klebsiella pneumoniae carbapenemase (KPC). ...Klebsiella pneumoniae harboring blaKPC (KPC-Kpn) is endemic in many areas including the United States, where the epidemic was primarily mediated by the clonal dissemination of Kpn ST258. We postulated that the spread of blaKPC in other regions occurs by different and more complex mechanisms. To test this, we investigated the evolution and dynamics of spread of KPC-Kpn in Colombia, where KPC became rapidly endemic after emerging in 2005.
Methods
We sequenced the genomes of 133 clinical isolates recovered from 24 tertiary care hospitals located in 10 cities throughout Colombia, between 2002 (before the emergence of KPC-Kpn) and 2014. Phylogenetic reconstructions and evolutionary mapping were performed to determine temporal and genetic associations between the isolates.
Results
Our results indicate that the start of the epidemic was driven by horizontal dissemination of mobile genetic elements carrying blaKPC-2, followed by the introduction and subsequent spread of clonal group 258 (CG258) isolates containing blaKPC-3.
Conclusions
The combination of 2 evolutionary mechanisms of KPC-Kpn within a challenged health system of a developing country created the “perfect storm” for sustained endemicity of these multidrug-resistant organisms in Colombia.
Many consumers depend on the contemporaneous growth of their food resources. For example, Tanytarsus gracilentus midges feed on algae, and because midge generation time is much longer than that of ...algae, individual midges benefit not just from the standing stock but also from the growth of algae during their lifespans. This implies that an intermediate consumption rate maximizes midge somatic growth: low consumption rates constrain midge growth because they do not fully utilize the available food, whereas high consumption rates suppress algal biomass growth and consequently limit future food availability. An experiment manipulating midge presence and initial algal abundance showed that midges can suppress algal growth, as measured by changes in algal gross primary production (GPP). We also found a positive relationship between GPP and midge growth. A consumer–resource model fit to the experimental data showed a hump‐shaped relationship between midge consumption rates and their somatic growth. In the model, predicted midge somatic growth rates were only positively associated with GPP when their consumption rate was below the value that optimized midge growth. Therefore, midges did not overexploit algae in the experiment. This work highlights the balance that consumers which depend on contemporaneous resource growth might have to strike between short‐term growth and future food availability, and the benefits for consumers when they ‘manage' their resources well.
The purpose of this study was to determine the efficacy of a cognitive-behavioral-based physical therapy (CBPT) program for improving outcomes in patients after lumbar spine surgery. A randomized ...controlled trial was conducted on 86 adults undergoing a laminectomy with or without arthrodesis for a lumbar degenerative condition. Patients were screened preoperatively for high fear of movement using the Tampa Scale for Kinesiophobia. Randomization to either CBPT or an education program occurred at 6 weeks after surgery. Assessments were completed pretreatment, posttreatment and at 3-month follow-up. The primary outcomes were pain and disability measured by the Brief Pain Inventory and Oswestry Disability Index. Secondary outcomes included general health (SF-12) and performance-based tests (5-Chair Stand, Timed Up and Go, 10-Meter Walk). Multivariable linear regression analyses found that CBPT participants had significantly greater decreases in pain and disability and increases in general health and physical performance compared with the education group at the 3-month follow-up. Results suggest a targeted CBPT program may result in significant and clinically meaningful improvement in postoperative outcomes. CBPT has the potential to be an evidence-based program that clinicians can recommend for patients at risk for poor recovery after spine surgery.
This study investigated a targeted cognitive-behavioral-based physical therapy program for patients after lumbar spine surgery. Findings lend support to the hypothesis that incorporating cognitive-behavioral strategies into postoperative physical therapy may address psychosocial risk factors and improve pain, disability, general health, and physical performance outcomes.
Understanding how nutrient limitation affects algal biomass and production is a long‐standing interest in aquatic ecology. Nutrients can influence these whole‐community characteristics through ...several mechanisms, including shifting community composition. Therefore, incorporating the joint responses of biomass, taxonomic composition, and production of algal communities, and relationships among them, is important for understanding effects of nutrient enrichment.
In shallow subarctic Lake Mývatn, Iceland, benthic algae compose a majority of whole‐lake primary production, support high secondary production, and influence nutrient cycling. Given the importance of these ecosystem processes, the factors that limit benthic algae have a large effect on the function and dynamics of the Mývatn system.
In a 33‐day nutrient enrichment experiment conducted in Lake Mývatn, we measured the joint responses of benthic algal biomass, primary production, and composition to nitrogen (N) and phosphorus (P) supplementation. We enriched N and P using nutrient‐diffusing agar overlain by sediment, with three levels of N and P that were crossed in a factorial design.
We found little evidence of community‐wide nutrient limitation, as chlorophyll‐a concentrations showed a negligible response to nutrients. Gross primary production (GPP) was unaffected by P and inhibited by N enrichment after 10 days, although the inhibitory effect of N diminished by day 33.
In contrast to biomass and primary production, community composition was strongly affected by N and marginally affected by P, with some algal groups increasing and others decreasing with enrichment. The taxa with the most negative and positive responses to N enrichment were Fragilariaceae and Scenedesmus, respectively.
The abundances of particular algal groups, based on standardised cell counts, were related to GPP measured at the end of the experiment. Oocystis was negatively associated with GPP but was unaffected by N or P, while Fragilariaceae and Scenedesmus were positively associated with GPP but had opposite responses to N. As a result, nutrient‐induced compositional shifts did not alter GPP.
Overall, our results show that nutrient enrichment can have large effects on algal community composition while having little effect on total biomass and primary production. Our study suggests that nutrient‐driven compositional shifts may not alter the overall ecological function of algal communities if (1) taxa have contrasting responses to nutrient enrichment but have similar effects on ecological processes, and/or (2) taxa that have strong influences on ecological function are not strongly affected by nutrients.
PDF
