Light pollution increases West Nile virus competence of a ubiquitous passerine reservoir species

Scaling artificial light at night and disease vector interactions into socio-ecological systems: a conceptual appraisal

There is burgeoning interest in how artificial light at night (ALAN) interacts with disease vectors, particularly mosquitoes. ALAN can alter mosquito behaviour and biting propensity, and so must alter disease transfer rates. However, most studies to date have been laboratory-based, and it remains unclear how ALAN modulates disease vector risk. Here, we identify five priorities to assess how artificial light can influence disease vectors in socio-ecological systems. These are to (i) clarify the mechanistic role of artificial light on mosquitoes, (ii) determine how ALAN interacts with other drivers of global change to influence vector disease dynamics across species, (iii) determine how ALAN interacts with other vector suppression strategies, (iv) measure and quantify the impact of ALAN at scales relevant for vectors, and (v) overcome the political and social barriers in implementing it as a novel vector suppression strategy. These priorities must be addressed to evaluate the costs and benefits of employing appropriate ALAN regimes in complex socio-ecological systems if it is to reduce disease burdens, especially in the developing world. This article is part of the theme issue 'Light pollution in complex ecological systems'.

Understanding Organisms Using Ecological Observatory Networks

Human activities are rapidly changing ecosystems around the world. These changes have widespread implications for the preservation of biodiversity, agricultural productivity, prevalence of zoonotic diseases, and sociopolitical conflict. To understand and improve the predictive capacity for these and other biological phenomena, some scientists are now relying on observatory networks, which are often composed of systems of sensors, teams of field researchers, and databases of abiotic and biotic measurements across multiple temporal and spatial scales. One well-known example is NEON, the US-based National Ecological Observatory Network. Although NEON and similar networks have informed studies of population, community, and ecosystem ecology for years, they have been minimally used by organismal biologists. NEON provides organismal biologists, in particular those interested in NEON's focal taxa, with an unprecedented opportunity to study phenomena such as range expansions, disease epidemics, invasive species colonization, macrophysiology, and other biological processes that fundamentally involve organismal variation. Here, we use NEON as an exemplar of the promise of observatory networks for understanding the causes and consequences of morphological, behavioral, molecular, and physiological variation among individual organisms.

House Sparrows Vary Seasonally in Their Ability to Transmit West Nile Virus

AbstractSeasonality in infectious disease prevalence is predominantly attributed to changes in exogenous risk factors. For vectored pathogens, high abundance, activity, and/or diversity of vectors can exacerbate disease risk for hosts. Conversely, many host defenses, particularly immune responses, are seasonally variable. Seasonality in host defenses has been attributed, in part, to the proximate (i.e., metabolic) and ultimate (i.e., reproductive fitness) costs of defense. In this study, our goal was to discern whether any seasonality is observable in how a common avian host, the house sparrow (Passer domesticus), copes with a common zoonotic arbovirus, the West Nile virus (WNV), when hosts are studied under controlled conditions. We hypothesized that if host biorhythms play a role in vector-borne disease seasonality, birds would be most vulnerable to WNV when breeding and/or molting (i.e., when other costly physiological activities are underway) and thus most transmissive of WNV at these times of year (unless birds died from infection). Overall, the results only partly supported our hypothesis. Birds were most transmissive of WNV in fall (after their molt is complete and when WNV is most prevalent in the environment), but WNV resistance, WNV tolerance, and WNV-dependent mortality did not vary among seasons. These results collectively imply that natural arboviral cycles could be partially underpinned by endogenous physiological changes in hosts. However, other disease systems warrant study, as this result could be specific to the nonnative and highly commensal nature of the house sparrow or a consequence of the relative recency of the arrival of WNV to the United States.

Impact of Human Activities on Disease-Spreading Mosquitoes in Urban Areas

Urbanization is one of the leading global trends of the twenty-first century that has a significant impact on health. Among health challenges caused by urbanization, the relationship of urbanization between emergence and the spread of mosquito-borne infectious diseases (MBIDs) is a great public health concern. Urbanization processes encompass social, economic, and environmental changes that directly impact the biology of mosquito species. In particular, urbanized areas experience higher temperatures and pollution levels than outlying areas but also favor the development of infrastructures and objects that are favorable to mosquito development. All these modifications may influence mosquito life history traits and their ability to transmit diseases. This review aimed to summarize the impact of urbanization on mosquito spreading in urban areas and the risk associated with the emergence of MBIDs. Moreover, mosquitoes are considered as holobionts, as evidenced by numerous studies highlighting the role of mosquito-microbiota interactions in mosquito biology. Taking into account this new paradigm, this review also represents an initial synthesis on how human-driven transformations impact microbial communities in larval habitats and further interfere with mosquito behavior and life cycle in urban areas.

Integrated molecular and behavioural data reveal deep circadian disruption in response to artificial light at night in male Great tits (Parus major)

Globally increasing levels of artificial light at night (ALAN) are associated with shifting rhythms of behaviour in many wild species. However, it is unclear whether changes in behavioural timing are paralleled by consistent shifts in the molecular clock and its associated physiological pathways. Inconsistent shifts between behavioural and molecular rhythms, and between different tissues and physiological systems, disrupt the circadian system, which coordinates all major body functions. We therefore compared behavioural, transcriptional and metabolomic responses of captive great tits (Parus major) to three ALAN intensities or to dark nights, recording activity and sampling brain, liver, spleen and blood at mid-day and midnight. ALAN advanced wake-up time, and this shift was paralleled by advanced expression of the clock gene BMAL1 in all tissues, suggesting close links between behaviour and clock gene expression across tissues. However, further analysis of gene expression and metabolites revealed that clock shifts were inconsistent across physiological systems. Untargeted metabolomic profiling showed that only 9.7% of the 755 analysed metabolites followed the behavioural shift. This high level of desynchronization indicates that ALAN disrupted the circadian system on a deep, easily overlooked level. Thus, circadian disruption could be a key mediator of health impacts of ALAN on wild animals.

Artificial Light as a Modulator of Mosquito-Borne Disease Risk

Light is a fundamental cue regulating a host of biological responses. The artificial modification thereof demonstrably impacts a wide range of organisms. The use of artificial light is changing in type, extent and intensity. Insect vector-borne diseases remain a global scourge, but surprisingly few studies have directly investigated the interactions between artificial light and disease vectors, such as mosquitoes. Here we briefly overview the progress to date, which highlights that artificial light must be considered as a modulator of mosquito-borne disease risk. We discuss where the mechanisms may lie, and where future research could usefully be directed, particularly in advancing understanding of the biological effects of the light environment. Further understanding of how artificial light may modulate mosquito-borne disease risk may assist in employing and redesigning light regimes that do not increase, and may even mitigate, already significant disease burdens, especially in the developing world.

Trade-Offs (and Constraints) in Organismal Biology

AbstractTrade-offs and constraints are inherent to life, and studies of these phenomena play a central role in both organismal and evolutionary biology. Trade-offs can be defined, categorized, and studied in at least six, not mutually exclusive, ways. (1) Allocation constraints are caused by a limited resource (e.g., energy, time, space, essential nutrients), such that increasing allocation to one component necessarily requires a decrease in another (if only two components are involved, this is referred to as the Y-model, e.g., energy devoted to size versus number of offspring). (2) Functional conflicts occur when features that enhance performance of one task decrease performance of another (e.g., relative lengths of in-levers and out-levers, force-velocity trade-offs related to muscle fiber type composition). (3) Shared biochemical pathways, often involving integrator molecules (e.g., hormones, neurotransmitters, transcription factors), can simultaneously affect multiple traits, with some effects being beneficial for one or more components of Darwinian fitness (e.g., survival, age at first reproduction, fecundity) and others detrimental. (4) Antagonistic pleiotropy describes genetic variants that increase one component of fitness (or a lower-level trait) while simultaneously decreasing another. (5) Ecological circumstances (or selective regime) may impose trade-offs, such as when foraging behavior increases energy availability yet also decreases survival. (6) Sexual selection may lead to the elaboration of (usually male) secondary sexual characters that improve mating success but handicap survival and/or impose energetic costs that reduce other fitness components. Empirical studies of trade-offs often search for negative correlations between two traits that are the expected outcomes of the trade-offs, but this will generally be inadequate if more than two traits are involved and especially for complex physiological networks of interacting traits. Moreover, trade-offs often occur only in populations that are experiencing harsh environmental conditions or energetic challenges at the extremes of phenotypic distributions, such as among individuals or species that have exceptional athletic abilities. Trade-offs may be (partially) circumvented through various compensatory mechanisms, depending on the timescale involved, ranging from acute to evolutionary. Going forward, a pluralistic view of trade-offs and constraints, combined with integrative analyses that cross levels of biological organization and traditional boundaries among disciplines, will enhance the study of evolutionary organismal biology.

Light at night disrupts biological clocks, calendars, and immune function

Light at night is a pervasive problem in our society; over 80% of the world’s population experiences significant light pollution. Exacerbating this issue is the reality that artificially lit outdoor areas are growing by 2.2% per year and continuously lit areas brighten by 2.2% each year due to the rapid growths in population and urbanization. Furthermore, the increase in the prevalence of night shift work and smart device usage contributes to the inescapable nature of artificial light at night (ALAN). Although previously assumed to be innocuous, ALAN has deleterious effects on the circadian system and circadian-regulated physiology, particularly immune function. Due to the relevance of ALAN to the general population, it is important to understand its roles in disrupting immune function. This review presents a synopsis of the effects of ALAN on circadian clocks and immune function. We delineate the role of ALAN in altering clock gene expression and suppressing melatonin. We review the effects of light at night on inflammation and the innate and adaptive immune systems in various species to demonstrate the wide range of ALAN consequences. Finally, we propose future directions to provide further clarity and expansion of the field.

Introduction to the Symposium: Effects of Light Pollution Across Diverse Natural Systems

Light pollution, or the presence of artificial light at night (ALAN), is among the fastest growing but least understood anthropogenic stressor on the planet. While historically light pollution has not received attention comparable to climate change or chemical pollution, research over the past several decades has revealed the plethora of negative effects on humans, animals, and supporting ecosystems. As light pollution continues to grow in spatial, spectral, and temporal extent, we recognize the urgent need to understand how this affects circadian physiology, organismal fitness, life history traits and tradeoffs, population trends, and community interactions. Here, we aim to highlight background and foundational evidence of the effects of light pollution to present context and the basis for early light pollution studies. Next, we touch on several understudied topics where research is underway to fill gaps in our knowledge and provide the basis for future research. Last, we focus on questions that are vital to understanding the effects of ALAN on diverse natural systems and discuss the barriers we face conducting research on light pollution.

Wavelength-dependent effects of artificial light at night on phytoplankton growth and community structure

Artificial light at night (ALAN) is a disruptive form of pollution, impacting physiological and behavioural processes that may scale up to population and community levels. Evidence from terrestrial habitats show that the severity and type of impact depend on the wavelength and intensity of ALAN; however, research on marine organisms is still limited. Here, we experimentally investigated the effect of different ALAN colours on marine primary producers. We tested the effect of green (525 nm), red (624 nm) and broad-spectrum white LED ALAN, compared to a dark control, on the green microalgae Tetraselmis suesica and a diatom assemblage. We show that green ALAN boosted chlorophyll production and abundance in T. suesica. All ALAN wavelengths affected assemblage biomass and diversity, with red and green ALAN having the strongest effects, leading to higher overall abundance and selective dominance of specific diatom species, some known to cause harmful algal blooms. Our findings show that green and red ALAN should be used with caution as alternative LED colours in coastal areas, where there might be a need to strike a balance between the effects of green and red light on marine primary producers with the benefit they appear to bring to other organisms.

Dynamics of data availability in disease modeling: An example evaluating the trade-offs of ultra-fine-scale factors applied to human West Nile virus disease models in the Chicago area, USA

Background

Since 1999, West Nile virus (WNV) has moved rapidly across the United States, resulting in tens of thousands of human cases. Both the number of human cases and the minimum infection rate (MIR) in vector mosquitoes vary across time and space and are driven by numerous abiotic and biotic forces, ranging from differences in microclimates to socio-demographic factors. Because the interactions among these multiple factors affect the locally variable risk of WNV illness, it has been especially difficult to model human disease risk across varying spatial and temporal scales. Cook and DuPage Counties, comprising the city of Chicago and surrounding suburbs, experience some of the highest numbers of human neuroinvasive cases of WNV in the United States. Despite active mosquito control efforts, there is consistent annual WNV presence, resulting in more than 285 confirmed WNV human cases and 20 deaths from the years 2014–2018 in Cook County alone.

Methods

A previous Chicago-area WNV model identified the fifty-five most high and low risk locations in the Northwest Mosquito Abatement District (NWMAD), an enclave ¼ the size of the combined Cook and DuPage county area. In these locations, human WNV risk was stratified by model performance, as indicated by differences in studentized residuals. Within these areas, an additional two-years of field collections and data processing was added to a 12-year WNV dataset that includes human cases, MIR, vector abundance, and land-use, historical climate, and socio-economic and demographic variables, and was assessed by an ultra-fine-scale (1 km spatial x 1 week temporal resolution) multivariate logistic regression model.

Results

Multivariate statistical methods applied to the ultra-fine-scale model identified fewer explanatory variables while improving upon the fit of the previous model. Beyond MIR and climatic factors, efforts to acquire additional covariates only slightly improved model predictive performance.

Conclusions

These results suggest human WNV illness in the Chicago area may be associated with fewer, but increasingly critical, key variables at finer scales. Given limited resources, these findings suggest large variations in model performance occur, depending on covariate availability, and provide guidance in variable selection for optimal WNV human illness modeling.

Light pollution affects West Nile virus exposure risk across Florida

Emerging infectious diseases (EIDs) present global health threats, and their emergences are often linked to anthropogenic change. Artificial light at night (ALAN) is one form of anthropogenic change that spans beyond urban boundaries and may be relevant to EIDs through its influence on the behaviour and physiology of hosts and/or vectors. Although West Nile virus (WNV) emergence has been described as peri-urban, we hypothesized that exposure risk could also be influenced by ALAN in particular, which is testable by comparing the effects of ALAN on prevalence while controlling for other aspects of urbanization. By modelling WNV exposure among sentinel chickens in Florida, we found strong support for a nonlinear relationship between ALAN and WNV exposure risk in chickens with peak WNV risk occurring at low ALAN levels. Although our goal was not to discern how ALAN affected WNV relative to other factors, effects of ALAN on WNV exposure were stronger than other known drivers of risk (i.e. impervious surface, human population density). Ambient temperature in the month prior to sampling, but no other considered variables, strongly influenced WNV risk. These results indicate that ALAN may contribute to spatio-temporal changes in WNV risk, justifying future investigations of ALAN on other vector-borne parasites.

The Circadian Clock and Viral Infections

The circadian clock controls several aspects of mammalian physiology and orchestrates the daily oscillations of biological processes and behavior. Our circadian rhythms are driven by an endogenous central clock in the brain that synchronizes with clocks in peripheral tissues, thereby regulating our immune system and the severity of infections. These rhythms affect the pharmacokinetics and efficacy of therapeutic agents and vaccines. The core circadian regulatory circuits and clock-regulated host pathways provide fertile ground to identify novel antiviral therapies. An increased understanding of the role circadian systems play in regulating virus infection and the host response to the virus will inform our clinical management of these diseases. This review provides an overview of the experimental and clinical evidence reporting on the interplay between the circadian clock and viral infections, highlighting the importance of virus-clock research.

Drivers of Infectious Disease Seasonality: Potential Implications for COVID-19

Not 1 year has passed since the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19). Since its emergence, great uncertainty has surrounded the potential for COVID-19 to establish as a seasonally recurrent disease. Many infectious diseases, including endemic human coronaviruses, vary across the year. They show a wide range of seasonal waveforms, timing (phase), and amplitudes, which differ depending on the geographical region. Drivers of such patterns are predominantly studied from an epidemiological perspective with a focus on weather and behavior, but complementary insights emerge from physiological studies of seasonality in animals, including humans. Thus, we take a multidisciplinary approach to integrate knowledge from usually distinct fields. First, we review epidemiological evidence of environmental and behavioral drivers of infectious disease seasonality. Subsequently, we take a chronobiological perspective and discuss within-host changes that may affect susceptibility, morbidity, and mortality from infectious diseases. Based on photoperiodic, circannual, and comparative human data, we not only identify promising future avenues but also highlight the need for further studies in animal models. Our preliminary assessment is that host immune seasonality warrants evaluation alongside weather and human behavior as factors that may contribute to COVID-19 seasonality, and that the relative importance of these drivers requires further investigation. A major challenge to predicting seasonality of infectious diseases are rapid, human-induced changes in the hitherto predictable seasonality of our planet, whose influence we review in a final outlook section. We conclude that a proactive multidisciplinary approach is warranted to predict, mitigate, and prevent seasonal infectious diseases in our complex, changing human-earth system.

Artificial light at night alters the seasonal responses of biting mosquitoes

Urban light pollution caused by artificial light at night (ALAN) profoundly affects the ecology, behavior, and physiology of plants and animals. Further, this widespread environmental pollutant has the potential to negatively impact human and animal health by changing the seasonal dynamics of disease-transmitting insects. In response to short days, females of the Northern house mosquito enter an overwintering dormancy, or diapause. While in diapause, female mosquitoes divert energy away from reproduction, cease blood-feeding, and no longer transmit disease. We demonstrate that exposure to dim ALAN (~4 lx) causes female mosquitoes to avert diapause and become reproductively active, as these females acquired less fat content, developed larger egg follicles, imbibed vertebrate blood, and produced viable eggs and larvae. Our findings suggest that mosquitoes in highly light-polluted areas such as cities may be actively reproducing and biting later in the season, thereby extending the period of disease risk for urban residents. Our results suggest that ALAN should be considered when modeling mosquito abundance, disease risk, and when deciding how long mosquito surveillance and control should persist in temperate regions.

Artificial light at night amplifies seasonal relapse of haemosporidian parasites in a widespread songbird

Urban habitats can shape interactions between hosts and parasites by altering not only exposure rates but also within-host processes. Artificial light at night (ALAN) is common in urban environments, and chronic exposure can impair host immunity in ways that may increase infection. However, studies of causal links between this stressor, immunity, and infection dynamics are rare, particularly in migratory animals. Here, we experimentally tested how ALAN affects cellular immunity and haemosporidian parasite intensity across the annual cycle of migrant and resident subspecies of the dark-eyed junco (Junco hyemalis). We monitored an experimental group exposed to light at night and a control group under natural light/dark cycles as they passed through short days simulating early spring to longer days simulating the breeding season, followed by autumn migration. Using generalized additive mixed models, we show that ALAN increased inflammation, and leucocyte counts were greatest in early spring and autumn. At the start of the experiment, few birds had active infections based on microscopy, but PCR revealed many birds had chronic infections. ALAN increased parasitaemia across the annual cycle, with strong peaks in spring and autumn that were largely absent in control birds. As birds were kept in indoor aviaries to prevent vector exposure, this increased parasitaemia indicates relapse of chronic infection during costly life-history stages (i.e. reproduction). Although the immunological and parasitological time series were in phase for control birds, cross-correlation analyses also revealed ALAN desynchronized leucocyte profiles and parasitaemia, which could suggest a general exaggerated inflammatory response. Our study shows how a common anthropogenic influence can shape within-host processes to affect infection dynamics.

Genomic architecture of gapeworm resistance in a natural bird population

Parasites are recognized to be some of the strongest agents of natural selection, sometimes causing major changes in the phenotypes of their hosts. Understanding the genomic determinants leading to these adaptive processes is key to understand host-parasite interactions. However, dissecting the genetic architecture of host resistance in natural systems is difficult because of the multiple factors affecting these complex traits in the wild. In this issue of Molecular Ecology, Lundregan et al. (2020) use an impressive long-term data set to analyse the genomic architecture of host resistance to gapeworm in a metapopulation of house sparrows. The authors elegantly combine different approaches (variance component analyses, genome partitioning and genome-wide associations) to reveal that resistance to gapeworm is under polygenic control and can have both a significant additive genetic and dominance variance. This study is one of the first to simultaneously determine genomic architecture and assess additive genetic and dominance genetic variance in parasite resistance in natural populations.

Macroimmunology: The drivers and consequences of spatial patterns in wildlife immune defence

The prevalence and intensity of parasites in wild hosts varies across space and is a key determinant of infection risk in humans, domestic animals and threatened wildlife. Because the immune system serves as the primary barrier to infection, replication and transmission following exposure, we here consider the environmental drivers of immunity. Spatial variation in parasite pressure, abiotic and biotic conditions, and anthropogenic factors can all shape immunity across spatial scales. Identifying the most important spatial drivers of immunity could help pre-empt infectious disease risks, especially in the context of how large-scale factors such as urbanization affect defence by changing environmental conditions. We provide a synthesis of how to apply macroecological approaches to the study of ecoimmunology (i.e. macroimmunology). We first review spatial factors that could generate spatial variation in defence, highlighting the need for large-scale studies that can differentiate competing environmental predictors of immunity and detailing contexts where this approach might be favoured over small-scale experimental studies. We next conduct a systematic review of the literature to assess the frequency of spatial studies and to classify them according to taxa, immune measures, spatial replication and extent, and statistical methods. We review 210 ecoimmunology studies sampling multiple host populations. We show that whereas spatial approaches are relatively common, spatial replication is generally low and unlikely to provide sufficient environmental variation or power to differentiate competing spatial hypotheses. We also highlight statistical biases in macroimmunology, in that few studies characterize and account for spatial dependence statistically, potentially affecting inferences for the relationships between environmental conditions and immune defence. We use these findings to describe tools from geostatistics and spatial modelling that can improve inference about the associations between environmental and immunological variation. In particular, we emphasize exploratory tools that can guide spatial sampling and highlight the need for greater use of mixed-effects models that account for spatial variability while also allowing researchers to account for both individual- and habitat-level covariates. We finally discuss future research priorities for macroimmunology, including focusing on latitudinal gradients, range expansions and urbanization as being especially amenable to large-scale spatial approaches. Methodologically, we highlight critical opportunities posed by assessing spatial variation in host tolerance, using metagenomics to quantify spatial variation in parasite pressure, coupling large-scale field studies with small-scale field experiments and longitudinal approaches, and applying statistical tools from macroecology and meta-analysis to identify generalizable spatial patterns. Such work will facilitate scaling ecoimmunology from individual- to habitat-level insights about the drivers of immune defence and help predict where environmental change may most alter infectious disease risk.

Artificial Light at Night (ALAN): A Potential Anthropogenic Component for the COVID-19 and HCoVs Outbreak

The origin of the coronavirus disease 2019 (COVID-19) pandemic is zoonotic. The circadian day-night is the rhythmic clue to organisms for their synchronized body functions. The "development for mankind" escalated the use of artificial light at night (ALAN). In this article, we tried to focus on the possible influence of this anthropogenic factor in human coronavirus (HCoV) outbreak. The relationship between the occurrences of coronavirus and the ascending curve of the night-light has also been delivered. The ALAN influences the physiology and behavior of bat, a known nocturnal natural reservoir of many Coronaviridae. The "threatened" and "endangered" status of the majority of bat species is mainly because of the destruction of their proper habit and habitat predominantly through artificial illumination. The stress exerted by ALAN leads to the impaired body functions, especially endocrine, immune, genomic integration, and overall rhythm features of different physiological variables and behaviors in nocturnal animals. Night-light disturbs "virus-host" synchronization and may lead to mutation in the genomic part of the virus and excessive virus shedding. We also proposed some future strategies to mitigate the repercussions of ALAN and for the protection of the living system in the earth as well.

Distinct effects of acute versus chronic corticosterone exposure on Zebra finch responses to West Nile virus

Wild animals are exposed to both short- (acute) and long-term (chronic) stressors. The glucocorticoid hormones, such as corticosterone (CORT), facilitate coping with such stressors, but these hormones can have quite distinct effects contingent on the duration of their elevation. Previously, we found that experimental elevation of CORT for 2 days (via implantation) affected zebra finch (Taeniopygia guttata) responses to West Nile virus (WNV). CORT-elevated birds had higher viremia for at least 2 days longer than controls, and West Nile virus (WNV)-associated mortality occurred only in CORT-elevated birds. Here, we queried how acute elevations of CORT, via injection an hour prior to WNV exposure, would affect host responses, as short-term CORT elevations can be protective in other species. Although CORT injections and implantations elevated circulating CORT to a similar degree, the type of CORT exposure had quite distinct effects on WNV responses. CORT-implanted individuals reached higher viremia and suffered more mortality to WNV than control and CORT-injected individuals. However, CORT-implanted birds maintained body mass better during infection than the other two groups. Our results further support the possibility that chronic physiological stress affects aspects of host competence and potentially community-level WNV disease dynamics.

Parent and offspring genotypes influence gene expression in early life

Parents can have profound effects on offspring fitness. Little, however, is known about the mechanisms through which parental genetic variation influences offspring physiology in natural systems. White-throated sparrows (Zonotrichia albicollis, WTSP) exist in two genetic morphs, tan and white, controlled by a large polymorphic supergene. Morphs mate disassortatively, resulting in two pair types: tan male × white female (T × W) pairs, which provide biparental care and white male × tan female (W × T) pairs, which provide female-biased care. To investigate how parental composition impacts offspring, we performed RNA-seq on whole blood of WTSP nestlings sampled from nests of both pair types. Parental pair type had a large effect on nestling gene expression, with 881 genes differentially expressed (DE) and seven correlated gene coexpression modules. The DE genes and modules expressed at higher levels in W × T nests with female-biased parental care function in metabolism and stress-related pathways resulting from the overrepresentation of proteolysis and stress-response genes (e.g., SOD2, NR3C1). These results show that parental genotypes and/or associated behaviours influence nestling physiology, and highlight avenues of further research investigating the ultimate implications for the maintenance of this polymorphism. Nestlings also exhibited morph-specific gene expression, with 92 differentially expressed genes, comprising immunity genes and genes encompassed by the supergene. Remarkably, we identified the same regulatory hub genes in these blood-derived expression networks as were previously identified in adult WTSP brains (EPM2A, BPNT1, TAF5L). These hub genes were located within the supergene, highlighting the importance of this gene complex in structuring regulatory networks across diverse tissues.

Light pollution increases West Nile virus competence of a ubiquitous passerine reservoir species

Among the many anthropogenic changes that impact humans and wildlife, one of the most pervasive but least understood is light pollution. Although detrimental physiological and behavioural effects resulting from exposure to light at night are widely appreciated, the impacts of light pollution on infectious disease risk have not been studied. Here, we demonstrate that artificial light at night (ALAN) extends the infectious-to-vector period of the house sparrow (Passer domesticus), an urban-dwelling avian reservoir host of West Nile virus (WNV). Sparrows exposed to ALAN maintained transmissible viral titres for 2 days longer than controls but did not experience greater WNV-induced mortality during this window. Transcriptionally, ALAN altered the expression of gene regulatory networks including key hubs (OASL, PLBD1 and TRAP1) and effector genes known to affect WNV dissemination (SOCS). Despite mounting anti-viral immune responses earlier, transcriptomic signatures indicated that ALAN-exposed individuals probably experienced pathogen-induced damage and immunopathology, potentially due to evasion of immune effectors. A simple mathematical modelling exercise indicated that ALAN-induced increases of host infectious-to-vector period could increase WNV outbreak potential by approximately 41%. ALAN probably affects other host and vector traits relevant to transmission, and additional research is needed to advise the management of zoonotic diseases in light-polluted areas.