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At least 577 records · Page 32Linked to original sources
USGS2016

Interactions of landscape disturbances and climate change dictate ecological pattern and process: spatial modeling of wildfire, insect, and disease dynamics under future climates

Context Interactions among disturbances, climate, and vegetation influence landscape patterns and ecosystem processes. Climate changes, exotic invasions, beetle outbreaks, altered fire regimes, and human activities may interact to produce landscapes that appear and function beyond historical analogs. Objectives We used the mechanistic ecosystem-fire process model FireBGCv2 to model interactions of wildland fire, mountain pine beetle ( Dendroctonus ponderosae ), and white pine blister rust ( Cronartium ribicola ) under current and future climates, across three diverse study areas. Methods We assessed changes in tree basal area as a measure of landscape response over a 300-year simulation period for the Crown of the Continent in north-central Montana, East Fork of the Bitterroot River in western Montana, and Yellowstone Central Plateau in western Wyoming, USA. Results Interacting disturbances reduced overall basal area via increased tree mortality of host species. Wildfire decreased basal area more than beetles or rust, and disturbance interactions modeled under future climate significantly altered landscape basal area as compared with no-disturbance and current climate scenarios. Responses varied among landscapes depending on species composition, sensitivity to fire, and pathogen and beetle suitability and susceptibility. Conclusions Understanding disturbance interactions is critical for managing landscapes because forest responses to wildfires, pathogens, and beetle attacks may offset or exacerbate climate influences, with consequences for wildlife, carbon, and biodiversity.

Landscape Ecology↗
USGS2020

Influence of soil microbiota on Taxodium distichum seedling performance during extreme flooding events

Plant associations with soil microbiota can modulate tree seedling growth and survival via mutualistic or antagonistic interactions. It is uncertain, however, whether soil microbiota influence seedling growth of coastal trees when exposed to extreme flooding regimes. We evaluated the role of soil microbes in promoting baldcypress ( Taxodium distichum ) seedling performance under different inundation scenarios and determined the influence of flooding on the colonization of in planta beneficial microbes. Seedlings reared in sterile and non-sterile soil were exposed to three different flooding regimes historically experienced in Louisiana swamps. Seedling growth was assessed, and the colonization by beneficial symbionts such as arbuscular mycorrizhal fungi (AMF), and dark septate endophytes (DSE) was evaluated in harvested roots. Seedlings grown in sterile soil had six times higher growth than seedlings reared in non-sterile soil. As a result, we evaluated pathogen load in the roots by assessing oomycete colonization. Flooding influenced the in planta colonization of DSE and oomycetes, but did not affect the colonization of mutualist AMF fungi. DSE and oomycetes were rarer in flooded conditions, while AMF remained abundant. Seedling biomass production was not correlated with in planta fungal colonization or pathogen load. Soil microbiota can negatively influence baldcypress seedling growth, and no growth benefit was evidenced from the root colonization of mutualist fungi. Flooding can modify baldcypress-fungal interactions by diminishing colonization of DSE. Overall, baldycpress seedlings were more sensitive to the presence of microbiota than flooding, and thus restoration efforts should focus on having a better understanding of plant–microbe interactions in swamps.

Louisiana↗
USGS2021

Transient disease dynamics across ecological scales

Analyses of transient dynamics are critical to understanding infectious disease transmission and persistence. Identifying and predicting transients across scales, from within-host to community-level patterns, plays an important role in combating ongoing epidemics and mitigating the risk of future outbreaks. Moreover, greater emphases on non-asymptotic processes will enable timely evaluations of wildlife and human diseases and lead to improved surveillance efforts, preventive responses, and intervention strategies. Here, we explore the contributions of transient analyses in recent models spanning the fields of epidemiology, movement ecology, and parasitology. In addition to their roles in predicting epidemic patterns and endemic outbreaks, we explore transients in the contexts of pathogen transmission, resistance, and avoidance at various scales of the ecological hierarchy. Examples illustrate how (i) transient movement dynamics at the individual host level can modify opportunities for transmission events over time; (ii) within-host energetic processes often lead to transient dynamics in immunity, pathogen load, and transmission potential; (iii) transient connectivity between discrete populations in response to environmental factors and outbreak dynamics can affect disease spread across spatial networks; and (iv) increasing species richness in a community can provide transient protection to individuals against infection. Ultimately, we suggest that transient analyses offer deeper insights and raise new, interdisciplinary questions for disease research, consequently broadening the applications of dynamical models for outbreak preparedness and management.

Theoretical Ecology↗
USGS1994

Detection of Aeromonas salmonicida from water using a filtration method

Aeromonas salmonicida is a principal pathogen that contributes to mortality in hatchery-maintained Atlantic salmon that originated from the Connecticut and Merrimack rivers in the northeastern United States. Field tests were conducted to assess a filtration method for detection of A. salmonicida in water used to rear fishes. A presumptive identification of typical A. salmonicida was available within 72 h and the pathogen was confirmed within 96 h. This filtration method has been incorporated into daily management practices and provides results that allowed managers to make more informed decisions for fishery resources.

Aquaculture↗
USGS1996

The glycoprotein genes and gene junctions of the fish rhabdoviruses spring viremia of carp virus and hirame rhabdovirus: Analysis of relationships with other rhabdoviruses

The nucleotide sequences of the glycoprotein genes and all of the internal gene junctions of the fish pathogenic rhabdoviruses spring viremia of carp virus (SVCV) and hirame rhabdovirus (HIRRV) have been determined from cDNA clones generated from viral genomic RNA. The SVCV glycoprotein gene sequence is 1588 nucleotides (nt) long and encodes a 509 amino acid (aa) protein. The HIRRV glycoprotein gene sequence comprises 1612 nt, coding for a 508 aa protein. In sequence comparisons of 15 rhabdovirus glycoproteins, the SVCV glycoprotein gene showed the highest amino acid sequence identity (31.2-33.2%) with vesicular stomatitis New Jersey virus (VSNJV), Chandipura virus (CHPV) and vesicular stomatitis Indiana virus (VSIV). The HIRRV glycoprotein gene showed a very high amino acid sequence identity (74.3%) with the glycoprotein gene of another fish pathogenic rhabdovirus, infectious hematopoietic necrosis virus (IHNV), but no significant similarity with glycoproteins of VSIV or rabies virus (RABV). In phylogenetic analyses SVCV was grouped consistently with VSIV, VSNJV and CHPV in the Vesiculovirus genus of Rhabdoviridae. The fish rhabdoviruses HIRRV, IHNV and viral hemorrhagic septicemia virus (VHSV) showed close relationships with each other, but only very distant relationships with mammalian rhabdoviruses. The gene junctions are highly conserved between SVCV and VSIV, well conserved between IHNV and HIRRV, but not conserved between HIRRV/IHNV and RABV. Based on the combined results we suggest that the fish lyssa-type rhabdoviruses HIRRV, IHNV and VHSV may be grouped in their own genus within the family Rhabdoviridae. Aquarhabdovirus has been proposed for the name of this new genus.

Virus Research↗
USGS2013

Disease in a dynamic landscape: host behavior and wildfire reduce amphibian chytrid infection

Disturbances are often expected to magnify effects of disease, but these effects may depend on the ecology, behavior, and life history of both hosts and pathogens. In many ecosystems, wildfire is the dominant natural disturbance and thus could directly or indirectly affect dynamics of many diseases. To determine how probability of infection by the aquatic fungus Batrachochytrium dendrobatidis (Bd) varies relative to habitat use by individuals, wildfire, and host characteristics, we sampled 404 boreal toads ( Anaxyrus boreas boreas ) across Glacier National Park, Montana (USA). Bd causes chytridiomycosis, an emerging infectious disease linked with widespread amphibian declines, including the boreal toad. Probability of infection was similar for females and the combined group of males and juveniles. However, only 9% of terrestrial toads were infected compared to >30% of aquatic toads, and toads captured in recently burned areas were half as likely to be infected as toads in unburned areas. We suspect these large differences in infection reflect habitat choices by individuals that affect pathogen exposure and persistence, especially in burned forests where warm, arid conditions could limit Bd growth. Our results show that natural disturbances such as wildfire and the resulting diverse habitats can influence infection across large landscapes, potentially maintaining local refuges and host behaviors that facilitate evolution of disease resistance.

Montana↗
USGS2024

Vaccination of endangered wildlife as a conservation tool: Hindsights and new horizons in the pandemic era

Vaccines are an established conservation tool that can reduce the threat of infectious disease in endangered wildlife populations. Vaccines exist for many infectious pathogens, and at a time of rapid technological advances in vaccinology, developing vaccines and vaccination programs for free-living endangered wildlife could help efforts to prevent extinctions from disease threats. Vaccination efforts could focus on protecting members of the target species or could be directed at reservoir populations to prevent pathogen spillover. Vaccination strategies need to be substantiated by research on safety and effectiveness, include risk and feasibility assessments, account for differences in host biology and disease epidemiology, and align with relevant regulatory frameworks. Engagement with stakeholders and the public is important to ensure the success of endangered species vaccination programs. Challenges such as funding, regulation, and societal acceptance are barriers to progress in vaccination programs for some species and geographic regions. We recommend the development of scientifically based international guidelines and a transdisciplinary forum with a specific emphasis on endangered wildlife vaccination. New technologies could be used collaboratively to prevent transmission of diseases for which vaccines are not currently available. Careful approaches and enhanced collaborations could help ensure the successful development of wildlife vaccination programs and promote resilience of endangered wildlife populations to increasing anthropogenic and environmental stressors on biodiversity.

Biological Conservation↗
USGS2006

Conservation of Toll-like receptor signaling pathways in teleost fish

In mammals, toll-like receptors (TLR) recognize ligands, including pathogen-associated molecular patterns (PAMPs), and respond with ligand-specific induction of genes. In this study, we establish evolutionary conservation in teleost fish of key components of the TLR-signaling pathway that act as switches for differential gene induction, including MYD88, TIRAP, TRIF, TRAF6, IRF3, and IRF7. We further explore this conservation with a molecular phylogenetic analysis of MYD88. To the extent that current genomic analysis can establish, each vertebrate has one ortholog to each of these genes. For molecular tree construction and phylogeny inference, we demonstrate a methodology for including genes with only partial primary sequences without disrupting the topology provided by the high-confidence full-length sequences. Conservation of the TLR-signaling molecules suggests that the basic program of gene regulation by the TLR-signaling pathway is conserved across vertebrates. To test this hypothesis, leukocytes from a model fish, rainbow trout ( Oncorhynchus mykiss ), were stimulated with known mammalian TLR agonists including: diacylated and triacylated forms of lipoprotein, flagellin, two forms of LPS, synthetic double-stranded RNA, and two imidazoquinoline compounds (loxoribine and R848). Trout leukocytes responded in vitro to a number of these agonists with distinct patterns of cytokine expression that correspond to mammalian responses. Our results support the key prediction from our phylogenetic analyses that strong selective pressure of pathogenic microbes has preserved both TLR recognition and signaling functions during vertebrate evolution.

Comparative Biochemistry and Physiology, Part D: G↗
USGS2021

Neither microcystin, nor nodularin, nor cylindrospermopsin directly interact with human toll-like receptors

Various stressors including temperature, environmental chemicals, and toxins can have profound impacts on immunity to pathogens. Increased eutrophication near rivers and lakes coupled with climate change are predicted to lead to increased algal blooms. Currently, the effects of cyanobacterial toxins on disease resistance in mammals is a largely unexplored area of research. Recent studies have suggested that freshwater cyanotoxins can elicit immunomodulation through interaction with specific components of innate immunity, thus potentially altering disease susceptibility parameters for fish, wildlife, and human health owing to the conserved nature of the vertebrate immune system. In this study, we investigated the effects of three microcystin congeners (LR, LA, and RR), nodularin-R, and cylindrospermopsin for their ability to directly interact with nine different human Toll-like receptors (TLRs)—key pathogen recognition receptors for innate immunity. Toxin concentrations were verified by LC/MS/MS prior to use. Using an established HEK293-hTLR NF-κB reporter assay, we concluded that none of the tested toxins (29–90 nM final concentration) directly interacted with human TLRs in either an agonistic or antagonistic manner. These results suggest that earlier reports of cyanotoxin-induced NF-κB responses likely occur through different surface receptors to mediate inflammation.

Chemosphere↗
USGS2022

Novel insights on aquatic mammal MHC evolution: Evidence from manatee DQB diversity

The low diversity in marine mammal major histocompatibility complex (MHC) appears to support the hypothesis of reduced pathogen selective pressure in aquatic systems compared to terrestrial environments. However, the lack of characterization of the aquatic and evolutionarily distant Sirenia precludes drawing more generalized conclusions. Therefore, we aimed to characterize the MHC DQB diversity of two manatee species and compare it with those reported for marine mammals. Our results identified 12 and 6 alleles in T. inunguis and T. manatus , respectively. Alleles show high rates of nonsynonymous substitutions, suggesting loci are evolving under positive selection. Among aquatic mammals, Pinnipeda DQB had smaller numbers of alleles, higher synonymous substitution rate, and a dN/dS ratio closer to 1, suggesting it may be evolving under more relaxed selection compared to fully aquatic mammals. This contradicts one of the predictions of the hypothesis that aquatic environments impose reduced pathogen pressure to mammalian immune system. These results suggest that the unique evolutionary trajectories of mammalian MHC may impose challenges in drawing ecoevolutionary conclusions from comparisons across distant vertebrate lineages.

Florida↗
USGS2019

The evolving threat of rapid Ohia death (ROD) to Hawaii’s native ecosystems and rare plant species

Hawai‘i’s most widespread native tree, ‘ōhi‘a lehua ( Metrosideros polymorpha ), has been dying across large areas of Hawai‘i Island mainly due to two fungal pathogens ( Ceratocystis lukuohia and Ceratocystis huliohia ) that cause a disease collectively known as Rapid ‘Ōhi‘a Death (ROD). Here we examine patterns of positive detections of C. lukuohia as it has been linked to the larger mortality events across Hawai‘i Island. Our analysis compares the environmental range of C. lukuohia and its spread over time through the known climatic range and distribution of ‘ōhi‘a. Analyses show this fungal pathogen generally encompassed the core, but not the extremes of the climatic range of ‘ōhi‘a. We further modeled the potential distribution of C. lukuohia across the Hawaiian Archipelago to estimate the risk of ROD to other islands. Given the potential for C. lukuohia to alter the structure of ‘ōhi‘a dominated forests, we used our projected potential distribution of C. lukuohia to assess the risk of ROD to threatened and endangered plant species across Hawai‘i. Many native plants are likely vulnerable to these types of large ‘ōhi‘a mortality events: of 234 endangered native plant species considered, 147 (62.8%) have more than half of their range within current and expanding C. lukuohia suitable areas. We also found evidence that protecting habitat by fencing out introduced feral ungulates reduces the prevalence of the disease likely by reducing physical damage caused by these animals to ‘ōhi‘a trees, a precondition for Ceratocystis infection. Given the ongoing spread of C. lukuohia , we developed a dynamic web portal to host our results online, where models and analyses are updated with new lab-confirmed detections to provide managers with a useful tool to help monitor and assess the risk of C. lukuohia as it continues to spread.

Hawaii↗
USGS2019

Whitebark pine (Pinus albicaulis) growth and defense in response to mountain pine beetle outbreaks

Whitebark pine (Pinus albicaulis) is a critical forest species of Northern Rocky Mountain upper subalpine ecosystems, yet little is known about the physiological response of whitebark pine to disturbance (e.g. fire, bark beetles, and pathogens) across a range of diverse environmental gradients. Resin–based defenses have long been recognized as the primary mechanism by which conifers respond to attack by bark beetles and pathogens and several studies have linked resin duct properties to survivorship during periods of increased beetle activity. However, to our knowledge, no studies have compared axial resin ducts in the secondary xylem of whitebark pine across pairs of living and dead whitebark pine trees to better understand survivorship following multiple disturbances including mountain pine beetle and white pine blister rust. We found a clear distinction in growth and defense characteristics between live and dead whitebark pine. Across our study sites on the Flathead Indian Reservation in northwestern Montana, live whitebark pine produced larger resin ducts with a greater annual investment in resin–based defenses than whitebark pine that died. Resin duct size, duct area, and relative duct area were all greater in live whitebark pine (by 56%, 48%, and 57%, respectively) and these were the most important variables influencing whitebark pine survivorship. In contrast, whitebark pine that had died grew faster over time (22% larger ring widths) than their live counterparts and also produced more resin duct structures (20% more ducts on average). Whitebark pine at our study sites exhibit differing strategies in the allocation of resources toward growth and defense, with the majority of survivors of recent disturbance investing more in defensive structures than growth. Our results support the idea that maintaining genetic variability and the associated suite of differing physiological traits promotes diverse response strategies to a complex array of biophysical and biological stressors that might leave a species vulnerable to extinction across its range.

Northern Rocky Mountain↗
USGS2021

Growth and defense characteristics of whitebark pine (Pinus albicaulis) and lodgepole pine (Pinus contorta var latifolia) in a high-elevation, disturbance-prone mixed-conifer forest in northwestern Montana, USA

Recent, widespread tree mortality in the western U.S. resulting from changes in climate, pathogens, insect activity, and forest management practices has led to concerns for many ecologically and culturally important species. Within conifers, resin-based defenses have long been recognized as a primary defense mechanism against a variety of insects and pathogens. Oleoresin produced by trees contain complex mixtures of terpenoids that have numerous insecticidal and fungicidal properties. Research has also identified links between resin duct characteristics and increased probability of survival during bark beetle outbreaks. Whitebark pine ( Pinus albicaulis ) is a culturally significant high elevation species that provides numerous ecological services within subalpine and alpine ecosystems. Whitebark pine has co-evolved with a suite of biotic and abiotic disturbances. Individual trees allocate resources towards growth and resin-based defenses, making it a good candidate species to evaluate growth and defense relationships and tradeoffs. In this study we compared constitutive resin chemistry, tree growth and resin duct anatomy between similarly aged whitebark and lodgepole pine ( P. contorta var latifolia ) growing in proximity within a disturbance-prone, mixed-conifer forest in northwestern Montana. These two host species have varying degrees of historical exposure to mountain pine beetle. Our research yields four important findings. First, we did not find evidence of a tradeoff between tree growth and tree defenses (resin duct morphology and resin chemistry). This suggests that trees growing under favorable field conditions can experience high growth rates and still allocate ample resources towards defense. Second, we found that resin ducts and constitutive mono- and sesqui- terpenes were not correlated in lodgepole pine while duct production and area were positively related to constitutive monoterpenes, and duct size and area were positively related to constitutive sesquiterpenes, in whitebark pine. The lack of distinct, consistent relationships between these defensive features suggests that both whitebark and lodgepole pine trees present beetles with numerous, complex combinations of resin-based defenses. Third, based on constitutive terpene profiles, bark beetles are more likely to enter lodgepole pine but more likely to successfully elicit mass attacks in whitebark pine, which agrees with beetle attack and success patterns observed in the field. Fourth, overstory competition, particularly by Engelmann spruce ( Picea engelmannii ), can influence tree defenses, specifically by reducing constitutive terpene concentrations in lodgepole and whitebark pine. Competitive tree interactions could lead to altered bark beetle-conifer interactions as host and nonhost species migrate in response to changing climate. Our results suggest that strategies designed to support whitebark pine populations can benefit from better understanding interactions among growth, competition and physical and chemical defenses in response to multiple disturbance.

Montana↗
USGS2012

Production and characterization of monoclonal antibodies to IgM of Pacific herring ( Clupea pallasii )

Pacific herring ( Clupea pallasii ) have a central role in the North Pacific ecosystem as a forage fish species and are natural reservoirs of several important finfish pathogens, including Viral hemorrhagic septicemia virus (VHSV). Here, we report the identification of the gene encoding the immunoglobulin mu (IgM) heavy chain, as well as the development and characterization of monoclonal antibodies (MAbs) that specifically react with Pacific herring IgM. Pacific herring immunoglobulin was purified and consisted of heavy and light chains of approximately 80 and 25 kDa. Three hybridoma clones were initially identified by ELISA as reactive with purified immunoglobulin but only one clone was able to detect an 80 kDa protein in Pacific and Atlantic herring (Clupea harengus) whole plasma by denaturing western blot. However, all three MAbs were able to precipitate an 80 kDa protein from Pacific herring and LCMS sequencing of peptide fragments derived from this protein matched the predicted amino acid sequence of the cloned, heavy chain gene. In addition, two of the MAbs stained cells within the putative lymphocyte gates for the spleen, anterior kidney and posterior kidney but were not reactive for myeloid/granulocyte gates, which is consistent with these MAbs reacting with surface IgM + B-cells. To our knowledge, this is the first report of IgM-related gene sequences and anti-IgM monoclonal antibodies from any member of the family Clupeidae. The antibodies produced in this study are critical for achieving our long-term goal of conducting serological surveillance to assess pathogen exposure in natural populations of Pacific herring.

Fish and Shellfish Immunology↗
USGS2023

Characterization of maternal immunity following vaccination of broodstock against IHNV or Flavobacterium psychrophilum in rainbow trout (Oncorhynchus mykiss)

Infectious hematopoietic necrosis (IHN) is a significant viral disease affecting salmonids, whereas Flavobacterium psychrophilum (Fp), the causative agent of bacterial coldwater disease (BCWD), remains one of the most significant bacterial pathogens of salmonids. We explored maternal immunity in the context of IHN and BCWD management in rainbow trout ( Oncorhynchus mykiss ) aquaculture. Two experimental trials were conducted where different groups of female broodstock were immunized prior to spawning with an IHNV DNA vaccine or a live attenuated F. psychrophilum (Fp B.17-ILM) vaccine alone, or in combination. Progeny were challenged with either a low or high dose of IHNV at 13 days post hatch (dph) and 32 dph or challenged with F. psychrophilum at 13 dph. Mortality following a low-dose IHNV challenge at 13 dph was significantly lower in progeny from vaccinated broodstock vs. unvaccinated broodstock, but no significant differences were observed at 32 dph. Mortality due to BCWD was also significantly reduced in 13 dph fry that originated from broodstock immunized with the Fp B.17-ILM vaccine. After vaccination broodstock developed specific or neutralizing antibodies respectively to F. psychrophilum and IHNV; however, antibody titers in eggs and fry were undetectable. In the eggs and fry mRNA transcripts of the complement components C3 and C5 were detected at much higher levels in progeny from vaccinated broodstock and showed a significantly increased and rapid response post-challenge compared with unvaccinated broodstock. After challenges pro-inflammatory cytokine expression was immediately and considerably elevated in the fry from vaccinated broodstock vs. unvaccinated broodstock, whereas adaptive immune genes were elevated to a lesser degree. Results suggest that maternal transfer of innate and adaptive factors at the transcript level occurred because development of lymphomyeloid organs is not complete in such young fry. In addition to documenting maternally derived immunity in teleosts, this study demonstrates that broodstock vaccination can confer some degree of protection to progeny against viral and bacterial pathogens.

Fish and Shellfish Immunology↗
USGS2020

Climate’s cascading effects on disease, predation, and hatching success in Anaxyrus canorus, the threatened Yosemite toad

The U.S. Fish and Wildlife Service listed Anaxyrus canorus , the Yosemite toad, as federally threatened in 2014 based upon reported population declines and vulnerability to global-change factors. A. canorus lives only in California’s central Sierra Nevada at medium to sub-alpine elevations. Lands throughout its range are protected from development, but climate and other global-change factors potentially can limit populations. A. canorus reproduces in ultra-shallow wetlands that typically hydrate seasonally via melting of the winter snowpack. Lesser snowpacks in drier years can render wetland water volumes and hydroperiods insufficient to allow for successful breeding and reproduction. Additionally, breeding and embryogenesis occur very soon after wetlands thaw when overnight temperatures can be below freezing. Diseases, such as chytridiomycosis, which recently decimated regional populations of ranid species, also might cause declines of A. canorus populations. However, reported studies focused on whether climate interacts with any pathogens to affect fitness in A. canorus have been scarce. We investigated effects of these factors on A. canorus near Tioga Pass from 1996 to 2001. We found breeding subpopulations were distributed widely but inconsistently among potentially suitable wetlands and frequently consisted of small numbers of adults. We occasionally observed small but not alarming numbers of dead adults at breeding sites. In contrast, embryo mortality often was notably high, with the majority of embryos dead in some egg masses while mortality among coincidental Pseudacris regilla (Pacific treefrog) embryos in deeper water was lower. After sampling and experimentation, we concluded that freezing killed A. canorus embryos, especially near the tops of egg masses, which enabled Saprolegnia diclina (a water mold [Oomycota]) to infect and then spread through egg masses and kill more embryos, often in conjunction with predatory flatworms ( Turbellaria spp.). We also concluded exposure to ultraviolet-B radiation did not play a role. Based upon our assessments of daily minimum temperatures recorded around snow-off during years before and after our field study, the freezing potential we observed at field sites during embryogenesis might have been commonplace beyond the years of our field study. However, interactions among snow quantity, the timing of snow-off, and coincidental air temperatures that determine such freezing potential make projections of future conditions highly uncertain, despite overall warming trends. Our results describe important effects from ongoing threats to the fitness and abundance of A. canorus via reduced reproduction success and demonstrate how climate conditions can exacerbate effects from pathogens to threaten the persistence of amphibian populations.

California↗
USGS2024

Linking avian malaria parasitemia estimates from quantitative PCR and microscopy reveals new infection patterns in Hawai'i

Plasmodium parasites infect thousands of species and provide an exceptional system for studying host-pathogen dynamics, especially for multi-host pathogens. However, understanding these interactions requires an accurate assay of infection. Assessing Plasmodium infections using microscopy on blood smears often misses infections with low parasitemias (the fractions of cells infected), and biases in malaria prevalence estimates will differ among hosts that differ in mean parasitemias. We examined Plasmodium relictum infection and parasitemia using both microscopy of blood smears and quantitative polymerase chain reaction (qPCR) on 299 samples from multiple bird species in Hawai'i and fit models to predict parasitemias from qPCR cycle threshold (Ct) values. We used these models to quantify the extent to which microscopy underestimated infection prevalence and to more accurately estimate infection patterns for each species for a large historical study done by microscopy. We found that most qPCR-positive wild-caught birds in Hawaii had low parasitemias (Ct scores ≥35), which were rarely detected by microscopy. The fraction of infections missed by microscopy differed substantially among eight species due to differences in species’ parasitemia levels. Infection prevalence was likely 4–5-fold higher than previous microscopy estimates for three introduced species, including Zosterops japonicus , Hawaii’s most abundant forest bird, which had low average parasitemias. In contrast, prevalence was likely only 1.5–2.3-fold higher than previous estimates for Himatione sanguinea and Chlorodrepanis virens , two native species with high average parasitemias. Our results indicate that relative patterns of infection among species differ substantially from those observed in previous microscopy studies, and that differences depend on variation in parasitemias among species. Although microscopy of blood smears is useful for estimating the frequency of different Plasmodium stages and host attributes, more sensitive quantitative methods, including qPCR, are needed to accurately estimate and compare infection prevalence among host species.

Hawai'i↗
USGS2023

Coproduction and modeling spatial contact networks prevent bias about infectious hematopoietic necrosis virus transmission for Snake River Basin salmonids

Much remains unknown about variation in pathogen transmission across the geographic range of a free-ranging fish or animal species and about the influence of movement (associated with husbandry practices or animal behavior) on pathogen transmission. Salmonid hatcheries are an ideal system in which to study these processes. Salmonid hatcheries are managed for endangered species recovery, supplementation of threatened or at-risk fish stocks, support of fisheries, and ecosystem stability. Infectious hematopoietic necrosis virus (IHNV) is a rhabdovirus of significant concern to salmon aquaculture. Landscape IHNV transmission dynamics previously had been estimated only for salmonid hatcheries in the Lower Columbia River Basin (LCRB). The objectives of this study were to estimate IHNV transmission dynamics in a unique geographic region, the Snake River Basin (SRB), and to quantitatively estimate the effect of model coproduction on inference because previous assessments of coproduction have been qualitative. In contrast to the LCRB, the SRB has hatchery complexes consisting of a main hatchery and ≥1 satellite facility. Knowledge about hatchery complexes was held by a subset of project researchers but would not have been available to project modelers without coproduction. Project modelers generated and tested multiple versions of Bayesian susceptible-exposedinfected models to realistically represent the SRB and estimate the effect of coproduction. Models estimated the frequency of transmission routes, route-specific infection probabilities, and infection probabilities for combinations of salmonid hosts and IHNV lineages. Model results indicated that in the SRB, avoiding exposure to IHNV-positive adult salmonids is the most important action to prevent juvenile infections. Migrating adult salmonids exposed juvenile cohort-sites most frequently, and the infection probability was greatest following exposure to migrating adults. Without coproduction, the frequency of exposure by migrating adults would have been overestimated by 70 cohort-sites, and the infection probability following exposure to migrating adults would have been underestimated by∼0.09. The coproduced model had less uncertainty in the infection probability if no transmission route could be identified (Bayesian credible interval (BCI) width = 0.12) compared to the model without coproduction (BCI width = 0.34). Evidence for virus lineage MD specialization on steelhead and rainbow trout (both Oncorhynchus mykiss) was apparent without model coproduction. In the SRB, we found a greater probability of virus lineage UC infection in Chinook salmon (Oncorhynchus tshawytscha) compared to in O. mykiss, whereas in the LCRB, UC more clearly exhibited a generalist approach. Coproduction influenced estimates that depended on transmission routes, which operated differently at main hatcheries and satellite sites within hatchery complexes. Hatchery complexes are found outside of the SRB and are not specific to salmonid hatcheries alone. There is great potential for coproduction and modeling spatial contact networks to advance understanding about infectious disease transmission in complex production systems and surrounding free-ranging animal populations.

Idaho, Oregon, Washington↗