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At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

When can we detect lianas from space? Toward a mechanistic understanding of liana‐infested forest optics

Abstract Lianas, woody vines acting as structural parasites of trees, have profound effects on the composition and structure of tropical forests, impacting tree growth, mortality, and forest succession. Remote sensing could offer a powerful tool for quantifying the scale of liana infestation, provided the availability of robust detection methods. We analyze the consistency and global geographic specificity of spectral signals—reflectance across wavelengths—from liana‐infested tree crowns and forest stands, examining the underlying mechanisms of these signals. We compiled a uniquely comprehensive database, including leaf reflectance spectra from 5424 leaves, fine‐scale airborne reflectance data from 999 liana‐infested canopies, and coarse‐scale satellite reflectance data covering 775 ha of liana‐infested forest stands. To unravel the mechanisms of the liana spectral signal, we applied mechanistic radiative transfer models across scales, establishing a synthesis of the relative importance of different mechanisms, which we corroborate with field data on liana leaf chemistry and canopy structure. We find a consistent liana spectral signal at canopy and stand scales across globally distributed sites. This signature mainly arises at the canopy level due to direct effects of more horizontal leaf angles, resulting in a larger projected leaf area, and indirect effects from increased light scattering in the near and short‐wave infrared regions, linked to lianas' less costly leaf construction compared with trees on average. The existence of a consistent global spectral signal for lianas suggests that large‐scale quantification of liana infestation is feasible. However, because the traits responsible for the liana canopy‐reflectance signal are not exclusive to lianas, accurate large‐scale detection requires rigorously validated remote sensing methods. Our models highlight challenges in automated detection, such as potential misidentification due to leaf phenology, tree life history, topography, and climate, especially where the scale of liana infestation is less than a single remote sensing pixel. The observed cross‐site patterns also prompt ecological questions about lianas' adaptive similarities in optical traits across environments, indicating possible convergent evolution due to shared constraints on leaf biochemical and structural traits.

Environmental Sciences & Ecology↗
DOE OSTI2025

Resist! : Sustaining forest carbon sequestration and wood production after insect disturbance

Disturbances from insect pests threaten ecologically and economically important goods and services supplied by forests, including wood production and carbon sequestration. We highlight the factors that influence these services’ resistance, a term quantifying the initial response to disturbance. Insects inflict damage through a range of mechanisms, prompting distinct plant physiological responses that scale to influence ecosystem processes and, with time, goods and services. The degree and timing of tree mortality and defoliation affect the amount of residual vegetation available to support compensatory wood production and influence carbon sequestration by changing rates of detritus-fueled decomposition. Compounding, or sequential, insect attacks may prime a forest for additional disturbance, further eroding wood production and carbon sequestration. Forest management practices that promote biological and structural diversity, and augment or retain limiting biological and nutrient resources, may buffer against the effects of insect pests on wood production and carbon sequestration.

Gough, Christopher M. [Virginia Commonwealth Univ.↗
DOE OSTI2022

Strong parallel evidence of selection during switchgrass sward establishment in hybrid and lowland ecotypes

Switchgrass sward establishment results in up to 90% seedling mortality. The degree of selection during sward establishment has not been reported using modern genetic methods. Pooled leaf samples were sequenced from replicated swards of 46 half-sib families from two breeding groups (lowland and hybrid) before and through 3 years of stand establishment. Pooled allele frequencies were then assessed using fixation indices (Fst) and an independent data set was used to predict the polygenic impact of establishment selection on two traits (heading date and winter survivorship). Last, the DNA pools were assigned survival rankings to predict the sward survival genomically estimated breeding values within the training data set. Strong and parallel selection occured in both breeding groups. Five genomic regions exceeded the significant threshold of 99.9% in >10 families, indicating consistent selection across families and breeding groups. Polygenic trait predictions determined that establishment selection was partially associated with winter survivorship but resulted in variable heading date alterations. The genomewide variation is consistent with selection for a small number of related parental lines. This study observed strong selection for a small number of hybrid and coastal ecotype individuals which are promising germplasm sources for improved sward survival. This confirms prior reports of sward selection during grassland establishment and highlights the strength of pooled DNA sequencing for survival traits.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Pyroptosis by caspase11/4-gasdermin-D pathway in alcoholic hepatitis in mice and patients

Alcoholic hepatitis (AH) continues to be a disease with high mortality and no efficacious medical treatment. Although severe AH is presented as acute on chronic liver failure, what underlies this transition from chronic alcoholic steatohepatitis (ASH) to AH is largely unknown. To address this question, unbiased RNA sequencing and proteomic analyses were performed on livers of the recently developed AH mouse model, which exhibits the shift to AH from chronic ASH upon weekly alcohol binge, and these results are compared to gene expression profiling data from AH patients. This cross-analysis has identified Casp11 (CASP4 in humans) as a commonly up-regulated gene known to be involved in the noncanonical inflammasome pathway. Immunoblotting confirms CASP11/4 activation in AH mice and patients, but not in chronic ASH mice and healthy human livers. Gasdermin-D (GSDMD), which induces pyroptosis (lytic cell death caused by bacterial infection) downstream of CASP11/4 activation, is also activated in AH livers in mice and patients. CASP11 deficiency reduces GSDMD activation, bacterial load in the liver, and severity of AH in the mouse model. Conversely, the deficiency of interleukin-18, the key antimicrobial cytokine, aggravates hepatic bacterial load, GSDMD activation, and AH. Furthermore, hepatocyte-specific expression of constitutively active GSDMD worsens hepatocellular lytic death and polymorphonuclear leukocyte inflammation. Conclusion: These results implicate pyroptosis induced by the CASP11/4-GSDMD pathway in the pathogenesis of AH. (Hepatology 2018;67:1737-1753).

Khanova, Elena↗
DOE OSTI2017

Landscape heterogeneity reduces coyote predation on white-tailed deer fawns

Coyote (Canis latrans) predation on white-tailed deer (Odocoileus virginianus) fawns in southeastern North America has led to deer population declines in some areas. Research or management efforts initiated in response to coyote predation on fawns have primarily focused on implementation of reduced antlerless deer harvest or coyote control to mitigate population declines. Vegetation characteristics may influence coyote hunting efficiency, but the potential influence of land cover at large scales in the southeastern United States is underexplored. We investigated whether mortality risk was affected by landscape characteristics within fawn home ranges for a sample of 165 fawns on the United States Department of Energy’s Savannah River Site (SRS), South Carolina, 2007–2012. We monitored fawns every 8 hours to ≥ 4 weeks of age and 1–3 times daily to 12 weeks of age. We included only surviving or coyote-predated fawns in the dataset. The most supported model describing hazard ratios included the length of edge (i.e., area where 2 land cover types joined) in fawn home ranges. Probability of coyote predation increased 1.26 times for each 968-m decrease in edge within a fawn’s simulated home range (29.1-ha circular buffer) under this model. Further, fawns with the least edge in their home ranges were >2 times more likely to be depredated by a coyote than fawns with the greatest edge availability. Support for other models was relatively low, but informative variables (e.g., mean patch fractal dimension, Shannon’s diversity index, mean forest patch size) supported a general trend that as fawn home ranges became more homogeneous and contained larger patches with less edge and fewer cover types, predation risk increased. These findings are consistent with similar work in the midwestern United States, despite landscape differences between regions. The combined weight of evidence suggests maintenance of a heterogeneous landscape consisting of relatively small dispersed patches may reduce fawn losses to coyotes. In conclusion, this information may also be used to identify areas susceptible to greater fawn predation rates across large spatial scales. However, the relatively long forestry rotation lengths and large scale of consistent forest management on the SRS are uncommon in the southeastern United States and the mechanism for the pattern we observed is unclear. Therefore, our results may not be applicable to sites with different forest management practices.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Effect of compensatory immigration on the genetic structure of coyotes

Despite efforts to reduce their impacts on livestock and native ungulates within the southeastern United States, coyotes (Canis latrans) are able to recover from control programs. It is unknown how coyotes compensate for high mortality following trapping, so there is great interest to identify methods that can provide insight into coyote response to intensive trapping. To investigate if population genetic tools can decipher how coyotes recover from intensive trapping, we combined an empirical test of how genetic differentiation, diversity, and familial structure changed following trapping on the Savannah River Site (SRS), South Carolina with spatially explicit genetic simulations.The empirical dataset found that pre- and post-trapping periods had similar genetic diversities and were not genetically differentiated as expected by either compensatory reproduction or immigration from a single genetic source. The post-trapping coyote populations exhibited weaker signatures of philopatry with little evidence for increased dispersal distances of young coyotes, which suggests immigration caused a decrease in familial structure. Our simulations indicated that spatial autocorrelation coefficients and observed heterozygosities change as immigration increases while population differentiation, allelic richness, and displacement distances do not. Collectively, our results suggest that coyotes recover from intensive trapping via both reproduction and immigration, which likely makes preventing compensation difficult. Furthermore, monitoring post-trapping populations may offer more insight into maximizing the effectiveness of control efforts, and based on our simulations, population genetics can provide critical information about the amount of compensatory immigration following trapping.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Factors influencing pregnancy, litter size, and reproductive parameters of invasive wild pigs

Abstract Reproduction is the most energetically expensive life stage with the demands of productivity representing a balance between physiological requirements and environmental conditions. Wild pigs ( Sus scrofa ) throughout most of North America are genetic hybrids of feral domestic pigs and wild boar and have the highest reproductive potential of any wild ungulate. The phenology of reproduction, extent of multiple reproductive events per year, how individual and extrinsic factors contribute to variability in productivity, and impact of genetic lineage on these parameters is not well understood in wild pigs. We quantified reproductive parameters in wild pigs relative to a suite of individual and environmental attributes across seasons and multiple years in South Carolina, USA, from March 2017 and May 2020. We hypothesized that individual attributes (mass, age class, number of teats, rump fat, relative genetic association to wild boar vs. domestic pigs) and extrinsic factors (mast availability) would influence probability of pregnancy and fetal litter size. Wild pigs produced offspring throughout all months with peaks in conception corresponding to a seasonal pulse in food availability. The likelihood of pregnancy was influenced by female mass and nutritional condition and was greatest during years with abundant resources. Similarly, litter size increased with female mass and age, implying larger and older females represent the most important group for population recruitment. In evaluating the relationship between reproductive output and ancestral associations to domestic pigs versus wild boar, the proportion of wild boar ancestry was not an important influence on productivity in our population. We determined juveniles reach a physiological threshold of sexual maturity at approximately 30 kg. Average litter size was comparable to other populations, and wild pigs maintain an average fetal litter size of 5.43 offspring despite 13.6% embryonic mortality. A thorough understanding of biotic and extrinsic factors influencing reproduction are important for realistic population models, which are necessary for identifying areas to focus management needs and implementation.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

The Thermodynamic Links between Substrate, Enzyme, and Microbial Dynamics in Michaelis-Menten-Monod Kinetics

Accurate prediction of the temperature response of the velocity v of a biochemical reaction has wide applications in cell biology, reaction design, and biomass yield enhancement. Here in this study, we introduce a simple but comprehensive mechanistic approach that uses thermodynamics and biochemical kinetics to describe and link the reaction rate and Michaelis–Menten constants (k T and K T ) with the biomass yield and mortality rate (Y T and δ T ) as explicit functions of T . The temperature control is exerted by catabolic enthalpy at low temperatures and catabolic entropy at high temperatures, whereas changes in cell and enzyme–substrate heat capacity shift the anabolic electron use efficiency e A and the maximum reaction velocity v max . We show that cells have optimal growth when the catabolic (differential) free energy of activation decreases the cell free energy harvest required to duplicate their internal structures as long as electrons for anabolism are available. Lastly, with the described approach, we accurately predicted observed glucose fermentation and ammonium nitrification dynamics across a wide temperature range with a minimal number of thermodynamics parameters, and we highlight how kinetic parameters are linked to each other using first principles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Stock-specific spatial overlap among seabird predators and Columbia River juvenile Chinook Salmon suggests a mechanism for predation during early marine residence

Abstract Objective Because predation is thought to be the primary source of natural mortality for juvenile salmon first entering the ocean, we sought to identify regions where, on average, stock-specific spatial overlap between the distribution of threatened and endangered juvenile Chinook Salmon Oncorhynchus tshawytscha and abundant fish-eating seabirds (common murres Uria aalge and sooty shearwaters Ardenna grisea) suggests the greatest potential for ocean predation risk to juvenile Chinook Salmon. Methods The relative abundance and spatial distribution of seabird predators and juvenile Chinook Salmon were quantified as part of long-term ecosystem surveys during May 2003–2012 and June 2003–2022. Genetic stock identification methods were used to assign individual fish to their respective stock groups. Stock-specific species distribution models then generated maps and indices of average annual spatial overlap between predators and prey within the survey area. Result There is unequivocal evidence for spatial overlap between common murres, sooty shearwaters, and five genetic groups of interior and lower Columbia River juvenile Chinook Salmon. We found strongly positive (≥0.70) spatial correlations between predator and prey densities in both May and June, although spatial overlap was, in general, greater during May. The region of highest spatial overlap occurred on the inner continental shelf between the Columbia River mouth (46.2°N) and Grays Harbor (47.0°N), a region at the beginning of the juvenile salmon migratory pathway that is strongly affected by freshwater outflow from the river. Conclusion Our findings support the idea that ocean avian predation during early marine residence has the potential to affect marine survival of juvenile Chinook Salmon and should be further investigated to better inform and implement ecological models and possible recovery actions for Chinook Salmon populations of the Columbia River basin.

Zamon, Jeannette E.↗
DOE OSTI2018

Juvenile Chinook Salmon Survival When Exposed to Simulated Dam Passage after Being Implanted with a New Microacoustic Transmitter

The current minimum size for tagging Chinook Salmon Oncorhynchus tshawytscha with acoustic transmitters is = 95 mm fork length (FL). Using a new injectable acoustic transmitter (AT), our objective was to determine a minimum size for tagging Chinook Salmon. We measured survival and transmitter and tissue retention after exposure to rapid pressure changes (n = 399) or shear forces (n = 308). Fish (69–107 mm FL) were implanted with an AT (0.22 g; AT-only) or an AT and a passive integrated transponder (PIT; 0.10 g; AT+PIT) tag through a 3-mm incision with no sutures, or did not receive an incision or tag (control). Survival and transmitter and tissue retention following pressure changes was significantly lower for AT-only (0.70) and AT+PIT (0.54) fish compared to controls (0.85). No transmitters were expelled but 2.2% of AT-only and 12.5% of AT+PIT fish had tissue or a transmitter protruding. Following shear exposure, survival and transmitter and tissue retention was significantly lower for AT-only (0.70) and AT+PIT (0.61) fish compared to controls (0.98). Here, tissue expulsion described 87% of AT-only and 80% of AT+PIT mortalities. In both tests fish larger than 85–88 mm FL had a higher probability of survival and tissue and transmitter retention than smaller fish. We recommend the minimum size for tagging continue to be 95 mm FL, using a 3-mm incision with no sutures.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

How Small Can We Go? Evaluating Survival, Tag Retention, and Growth of Juvenile Chinook Salmon Implanted with a New Acoustic Microtag

Abstract Recently, an acoustic microtag, called the Eel–Lamprey Acoustic Tag (ELAT), was developed for use in juvenile American Eel Anguilla rostrata and Pacific Lamprey Entosphenus tridentatus. The ELAT (12.0 × 2.0 mm; 0.088 g in air) has the potential to be used to study other small-bodied fishes. In this pilot study, juvenile Chinook Salmon Oncorhynchus tshawytscha 52–99 mm fork length (FL) were surgically implanted with an ELAT (n = 99) or remained untagged (control; n = 101). Fish were held for 30 d to evaluate survival, tag retention, and growth. Survival did not differ significantly between control (n = 98 or 97.0%) and tagged fish (n = 95 or 95.9%). Logistic regression analysis suggested that survival was influenced by initial FL and tag burden. Mortalities only occurred in tagged fish with initial FLs of ≤65 mm (FL range = 57–65 mm; tag burdens = 3.8–5.9%). However, a tagged fish with an initial FL of 62 mm or an initial tag burden of 4.1% (FL range = 58–64 mm) was predicted to have a 90% chance of survival, and the smallest fish that survived the study was 54 mm FL (1.8 g; tag burden = 4.9%). Tag retention was high (99%), with only one fish expelling an ELAT during the study. Control fish grew slightly larger than the tagged individuals, but differences in final pooled FLs and weight gains were not significant. Our results demonstrate the successful surgical implantation of the ELAT into Chinook Salmon as small as 54 mm FL (1.8 g).

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Overwintering Distribution and Postspawn Survival of Steelhead in the Upper Columbia River Basin

Abstract Adult summer-run steelhead Oncorhynchus mykiss overwinter in freshwater for several months prior to spawning. In systems supporting mixed populations of fisheries and conservation importance, understanding the distribution and survival of pre- and postspawn fish is necessary for informed management. The upper Columbia River supports hatchery-origin components valued by anglers, natural-origin components of conservation concern, and temporary strays from downstream populations. We used radiotelemetry and PIT telemetry to monitor the behavior, distribution, and survival of adult steelhead during fall, overwintering, spawning, and postspawn periods, with a focus on use of the main stem versus four major tributaries. Adult steelhead (N = 807) were tagged at Priest Rapids Dam in 2015 and 2016. One-fifth of steelhead fell back below Priest Rapids Dam and did not reascend. A slight majority of tagged steelhead that overwintered upstream of Priest Rapids Dam did so in main-stem reservoirs (54%; N = 548). Overwintering in the main-stem Columbia River was more likely for later-arriving steelhead and was concentrated in the upstream-most reservoir. Winter tributary use was highest in the Wenatchee (26%; 2016) and Methow (18%; 2015) rivers, whereas no steelhead overwintered in the Entiat River. Harvest of hatchery-origin steelhead was 18% in 2015 and was near zero in 2016, when the fishery was suspended due to low adult returns. After accounting for reported harvest, annual overwinter survival did not differ between main-stem and tributary habitats, and relatively low adjusted survival of hatchery-origin steelhead in 2015 suggested unreported harvest. In contrast to low iteroparity rates (<3%), the majority of postspawn steelhead (56.5%) exited tributaries as kelts; kelt survival to Bonneville Dam was 65% in 2016 and 23% in 2017. Collectively, the results highlight the importance of understanding patterns of habitat use and mortality in steelhead populations when managers are faced with balancing harvest and conservation goals.

Fuchs, Nathaniel T.↗
DOE OSTI2019

A comparison of opioid‐involved fatalities captured in the National Poison Data System to data derived from US death certificate literal text

Abstract Purpose The purpose of the study is to describe and compare the number and characteristics of opioid‐involved fatal cases captured in the National Poison Data System (NPDS) and in US death certificates. Methods NPDS, which collects data on all calls to US poison control centers, and Drug‐Involved Mortality (DIM), which combines information from literal text of US death certificates and National Vital Statistics Systems, were queried for opioid‐involved fatal cases from 2010 to 2015. Characteristics of the two case series were compared. Results DIM contained 154 016 opioid‐involved overdose deaths, and NPDS contained 2524 fatal opioid exposures, a ratio of 61:1. The number of opioid deaths remained stable in NPDS but increased in DIM over the 6‐year period. On average, deaths involving opioids with higher mean dosage strength (in morphine milligram equivalents) per unit among dispensed prescriptions were more likely to be captured in DIM relative to NPDS, as compared with those with a lower mean dosage strength per unit. The increase in fentanyl‐related deaths seen in DIM since 2013 was not observed in NPDS. Conclusions NPDS is a valuable drug safety surveillance resource due to its timeliness and drug specificity. However, it captures only a small fraction of opioid‐involved fatal poisonings, and comparisons with data derived from death certificate literal text indicate that caution is warranted in making inferences about opioid‐involved fatality trends over time or comparisons across opioids.

Mallama, Celeste A.↗
DOE OSTI2020

Fine-root dynamics vary with soil depth and precipitation in a lown-utrient tropical forest in the Central Amazonia

A common assumption in tropical ecology is that root systems respond rapidly to climatic cues but that most of that response is limited to the uppermost layer of the soil, with relatively limited changes in deeper layers. However, this assumption has not been tested directly, preventing models from accurately predicting the response of tropical forests to environmental change. We measured seasonal dynamics of fine roots in a Central Amazonia mature forest using minirhizotrons to 90 cm depth, which were calibrated with fine roots extracted from soil cores. Root productivity and mortality in superficial soil layers were positively correlated with precipitation, whereas root standing length was greater during the dry periods at the deeper layers. Contrary to historical assumptions, a large fraction of fine-root standing biomass (46%) and productivity (41%) were found in soil layers deeper than 30 cm. Furthermore, root turnover decreased linearly with soil depth. Our findings demonstrate a strong relationship between fine-root dynamics and precipitation regimes in Central Amazonia. Our results also emphasize the importance of deep roots for accurate estimates of primary productivity and the interaction between roots and carbon, water, and nutrients.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Degradation in photovoltaic encapsulant transmittance: Results of the first PVQAT TG5 artificial weathering study

Reduced optical transmittance of encapsulants resulting from ultraviolet (UV) degradation is frequently identified as a cause of decreased performance through the service life of photovoltaic modules. However, the present module safety and qualification standards apply short UV doses, only capable of examining design robustness and 'infant mortality' failures. Furthermore, essential information remains unknown that might be used to screen encapsulants through product lifetime. We conducted an interlaboratory study to provide the understanding that will be used toward developing a higher-fidelity, more-rigorous UV weathering test. Five representative known formulations of poly (ethylene-co-vinyl acetate) were studied, in addition to one thermoplastic polyurethane material. Replicate laminated silica/polymer/silica specimens were examined at seven institutions using a variety of indoor chambers (including xenon, UVA-340, and metal-halide light sources). Specimens were artificially weathered for 180 cumulative days at steady-state accelerated test conditions, predesignated relative to the default irradiance of 1.0 W m-2 nm-1 at 340 nm, chamber temperature of 60 degrees C, and chamber relative humidity of 30%. The solar-weighted transmittance, yellowness index, and the UV cut-off wavelength - each determined from the measured hemispherical transmittance - are examined to provide understanding and guidance for the UV light source (type lamp and filters), temperature, and humidity used in accelerated UV aging tests. The relative efficacy of xenon-arc and UVA-340 fluorescent sources and the typical range of activation energy for degradation is quantified from the experiments.

14 SOLAR ENERGY↗
DOE OSTI2020

Metribuzin resistance via enhanced metabolism in a multiple herbicide resistant Lolium rigidum population

Abstract BACKGROUND The photosystem II (PSII)‐inhibiting herbicides are important for Australian farmers to control Lolium rigidum Gaud. and other weed species in trazine tolerant (TT)‐canola fields. A L. rigidum population (R) collected from a TT‐canola field from Western Australia showed multiple resistance to PSII, acetyl‐coenzyme A carboxylase (ACCase) and acetolactate synthase (ALS) inhibitors. The mechanisms of multiple resistance in this R population were determined. RESULTS The R population showed a low‐level (about 3.0‐fold) resistance to the PSII‐inhibiting herbicides metribuzin and atrazine. Sequencing of the psbA gene revealed no differences between the R and susceptible (S) sequences. Furthermore, [ 14 C]‐metribuzin experiments found no significant difference in metribuzin foliar uptake and translocation between the R and S plants. However, [ 14 C]‐metribuzin metabolism in R plants was 2.3‐fold greater than in S plants. The cytochrome P450 monooxygenase inhibitor piperonyl butoxide (PBO) enhanced plant mortality response to metribuzin and atrazine in both R and S populations. In addition, multiple resistance to ALS and ACCase inhibitors are due to known resistance mutations in ALS and ACCase genes. CONCLUSION The results demonstrate that enhanced metribuzin metabolism likely involving cytochrome P450 monooxygenase contributes to metribuzin resistance in Lolium rigidum. This is the first report of metabolic resistance to the PSII‐inhibiting herbicide metribuzin in Australian Lolium rigidum . © 2020 Society of Chemical Industry

Ma, Hongju↗
DOE OSTI2024

Molecular Evolution of the H5 and H7 Highly Pathogenic Avian Influenza Virus Haemagglutinin Cleavage Site Motif

ABSTRACT Avian influenza viruses are ubiquitous in the Anatinae subfamily of aquatic birds and occasionally spill over to poultry. Infection with low pathogenicity avian influenza viruses generally leads to subclinical or mild clinical disease. In contrast, highly pathogenic avian influenza viruses emerge from low pathogenic forms and can cause severe disease associated with extraordinarily high mortality rates. Here, we describe the natural history of avian influenza virus, with a focus on H5Nx and H7Nx subtypes, and the emergence of highly pathogenic forms; we review the biology of AIV; we examine cleavage of haemagglutinin by host cell enzymes with a particular emphasis on the biochemical properties of the proprotein convertases, and trypsin and trypsin‐like proteases; we describe mechanisms implicated in the functional evolution of the haemagglutinin cleavage site motif that leads to emergence of HPAIVs; and finally, we discuss the diversity of H5 and H7 haemagglutinin cleavage site sequence motifs. It is crucial to understand the molecular attributes that drive the emergence and evolution of HPAIVs with pandemic potential to inform risk assessments and mitigate the threat of HPAIVs to poultry and human populations.

Luczo, Jasmina M. [Australian Animal Health Labora↗