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Behavioural and physiological resistance are key to slowing epidemic spread. We explore the evolutionary and epidemic consequences of their different costs for the evolution of tolerance that trades off with resistance. Behavioural resistance affects social cohesion, with associated group-level costs, while the cost of physiological resistance accrues only to the individual. Further, resistance, and the associated reduction in transmission, benefit susceptible hosts directly, whereas infected hosts only benefit indirectly, by reducing transmission to kin. We therefore model the coevolution of transmission-reducing resistance expressed in susceptible hosts with resistance expressed in infected hosts, as a function of kin association, and analyse the effect on population-level outcomes. Using parameter values for guppies, Poecilia reticulata, and their gyrodactylid parasites, we find that: (1) either susceptible or infected hosts should invest heavily in resistance, but not both; (2) kin association drives investment in physiological resistance more strongly than in behavioural resistance; and (3) even weak levels of kin association can favour altruistic infected hosts that invest heavily in resistance (versus selfish tolerance), eliminating parasites. Overall, our finding that weak kin association affects the coevolution of infected and susceptible investment in both behavioural and physiological resistance suggests that kin selection may affect disease dynamics across systems.

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Choosing to mate with an infected partner has several potential fitness costs, including disease transmission and infection-induced reductions in fecundity and parental care. By instead choosing a mate with no, or few, parasites, animals avoid these costs and may also obtain resistance genes for offspring. Within a population, then, the quality of sexually selected ornaments on which mate choice is based should correlate negatively with the number of parasites with which a host is infected ("parasite load"). However, the hundreds of tests of this prediction yield positive, negative, or no correlation between parasite load and ornament quality. Here, we use phylogenetically controlled meta-analysis of 424 correlations from 142 studies on a wide range of host and parasite taxa to evaluate explanations for this ambiguity. We found that ornament quality is weakly negatively correlated with parasite load overall, but the relationship is more strongly negative among ornaments that can dynamically change in quality, such as behavioral displays and skin pigmentation, and thus can accurately reflect current parasite load. The relationship was also more strongly negative among parasites that can transmit during sex. Thus, the direct benefit of avoiding parasite transmission may be a key driver of parasite-mediated sexual selection. No other moderators, including methodological details and whether males exhibit parental care, explained the substantial heterogeneity in our data set. We hope to stimulate research that more inclusively considers the many and varied ways in which parasites, sexual selection, and epidemiology intersect.

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Microglia are key mediators of inflammatory responses within the brain, as they regulate pro-inflammatory responses while also limiting neuroinflammation via reparative phagocytosis. Thus, identifying genes that modulate microglial function may reveal novel therapeutic interventions for promoting better outcomes in diseases featuring extensive inflammation, such as stroke. To facilitate identification of potential mediators of inflammation, we performed single-cell RNA sequencing of aged mouse brains following stroke and found that Ifi27l2a was significantly up-regulated, particularly in microglia. The increased Ifi27l2a expression was further validated in microglial culture, stroke models with microglial depletion, and human autopsy samples. Ifi27l2a is known to be induced by interferons for viral host defense, however the role of Ifi27l2a in neurodegeneration is unknown. In vitro studies in cultured microglia demonstrated that Ifi27l2a overexpression causes neuroinflammation via reactive oxygen species. Interestingly, hemizygous deletion of Ifi27l2a significantly reduced gliosis in the thalamus following stroke, while also reducing neuroinflammation, indicating Ifi27l2a gene dosage is a critical mediator of neuroinflammation in ischemic stroke. Collectively, this study demonstrates that a novel gene, Ifi27l2a, regulates microglial function and neuroinflammation in the aged brain and following stroke. These findings suggest that Ifi27l2a may be a novel target for conferring cerebral protection post-stroke.

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While the link between the gut microbiome and host behaviour is well established, how the microbiomes of other organs correlate with behaviour remains unclear. Additionally, behaviour-microbiome correlations are likely sex-specific because of sex differences in behaviour and physiology, but this is rarely tested. Here, we tested whether the skin microbiome of the Trinidadian guppy, Poecilia reticulata, predicts fish activity level and shoaling tendency in a sex-specific manner. High-throughput sequencing revealed that the bacterial community richness on the skin (Faith's phylogenetic diversity) was correlated with both behaviours differently between males and females. Females with richer skin-associated bacterial communities spent less time actively swimming. Activity level was significantly correlated with community membership (unweighted UniFrac), with the relative abundances of 16 bacterial taxa significantly negatively correlated with activity level. We found no association between skin microbiome and behaviours among male fish. This sex-specific relationship between the skin microbiome and host behaviour may indicate sex-specific physiological interactions with the skin microbiome. More broadly, sex specificity in host-microbiome interactions could give insight into the forces shaping the microbiome and its role in the evolutionary ecology of the host.

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Parasites exploit hosts to replicate and transmit, but overexploitation kills both host and parasite. Predators may shift this cost-benefit balance by consuming infected hosts or changing host behaviour, but the strength of these effects remains unclear. Here we use field and lab data on Trinidadian guppies and their Gyrodactylus spp. parasites to show how differential predation pressure influences parasite virulence and transmission. We use an experimentally demonstrated virulence-transmission trade-off to parametrize a mathematical model in which host shoaling (as a means of anti-predator defence), increases contact rates and selects for higher virulence. Then we validate model predictions by collecting parasites from wild, Trinidadian populations; parasites from high-predation populations were more virulent in common gardens than those from low-predation populations. Broadly, our results indicate that reduced social contact selects against parasite virulence.

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Parasite transmission is the ability of pathogens to move between hosts. As a key component of the interaction between hosts and parasites, it has crucial implications for the fitness of both. Here, we review the transmission dynamics of Gyrodactylus species, which are monogenean ectoparasites of teleost fishes and a prominent model for studies of parasite transmission. Particularly, we focus on the most studied host­parasite system within this genus: guppies, Poecilia reticulata, and G. turnbulli/G. bullatarudis. Through an integrative literature examination, we identify the main variables affecting Gyrodactylus spread between hosts, and the potential factors that enhance their transmission. Previous research indicates that Gyrodactylids spread when their current conditions are unsuitable. Transmission depends on abiotic factors like temperature, and biotic variables such as gyrodactylid biology, host heterogeneity, and their interaction. Variation in the degree of social contact between hosts and sexes might also result in distinct dynamics. Our review highlights a lack of mathematical models that could help predict the dynamics of gyrodactylids, and there is also a bias to study only a few species. Future research may usefully focus on how gyrodactylid reproductive traits and host heterogeneity promote transmission and should incorporate the feedbacks between host behaviour and parasite transmission.

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BACKGROUND: CD146 is a tight junction-associated molecule involved in maintaining endothelial barrier, and balancing immune-inflammation response, in cardiovascular disease. Notably, peripheral CD146+ cells significantly upsurge under vessel dyshomeostasis such as acute myocardial injury (AMI), appearing to be a promising therapeutic target. In this study, with a new view of gene correlation, we aim at deciphering the complex underlying mechanism of CD146+ cells' impact in the development of AMI. METHODS: Transcription dataset GSE 66,360 of CD146+ blood cells from clinical subjects was downloaded from NCBI. Pearson networks were constructed and the clustering coefficients were calculated to disclose the differential connectivity genes (DCGs). Analysis of gene connectivity and gene expression were performed to reveal the hub genes and hub gene clusters followed by gene enrichment analysis. RESULTS AND CONCLUSIONS: Among the total 23,520 genes, 27 genes out of 126 differential expression genes were identified as DCGs. These DCGs were found in the periphery of the networks under normal condition, but transferred to the functional center after AMI. Moreover, it was revealed that DCGs spontaneously crowded together into two functional models, CCL20 cluster and NR4A3 cluster, influencing the CD146-mediated signaling pathways during the pathology of AMI for the first time.

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Secondary injury following cortical stroke includes delayed gliosis and eventual neuronal loss in the thalamus. However, the effects of aging and the potential to ameliorate this gliosis with NMDA receptor (NMDAR) antagonism are not established. We used the permanent distal middle cerebral artery stroke model (pdMCAO) to examine secondary thalamic injury in young and aged mice. At 3 days post-stroke (PSD3), slight microgliosis (IBA-1) and astrogliosis (GFAP) was evident in thalamus, but no infarct. Gliosis increased dramatically through PSD14, at which point degenerating neurons were detected. Flow cytometry demonstrated a significant increase in CD11b+/CD45int microglia (MG) in the ipsilateral thalamus at PSD14. CCR2-RFP reporter mouse further demonstrated that influx of peripheral monocytes contributed to the MG/Mϕ population. Aged mice demonstrated reduced microgliosis and astrogliosis compared with young mice. Interestingly, astrogliosis demonstrated glial scar-like characteristics at two years post-stroke, but not by 6 weeks. Lastly, treatment with memantine (NMDAR antagonist) at 4 and 24 h after stroke significantly reduced gliosis at PSD14. These findings expand our understanding of gliosis in the thalamus following cortical stroke and demonstrate age-dependency of this secondary injury. Additionally, these findings indicate that delayed treatment with memantine (an FDA approved drug) provides significant reduction in thalamic gliosis.

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BACKGROUND: Brain temperature is a strong determinant of ischemic stroke injury. For this reason, tight management of brain or body temperature (Tcore) in experimental rodent stroke models is recommended to improve the rigor and reproducibility of outcomes. However, methods for managing Tcore during and after stroke vary widely in approach and effectiveness. NEW METHOD: We developed a low-cost warm ambient air cage (WAAC) system to provide improved temperature control during the intra-ischemic and post-ischemic recovery periods. The system is incorporated into standard holding cages for maintaining Tcore during the intra-ischemic period as well as for several hours into the recovery period. RESULTS AND COMPARISON WITH EXISTING METHODS: We compared the WAAC system with a commonly used heat support method, consisting of a cage on a heating pad. Both heat support systems were evaluated for the middle cerebral artery occlusion (MCAo) stroke model in mice. The WAAC system provided improved temperature control (more normothermic Tcore and less Tcore variation) during the intra- ischemic period (60 min) and post-ischemic period (3 h). Mean infarct volume was not statistically different by heat support system, however, standard deviation was 54 % lower in the WAAC system group. CONCLUSIONS: Mice and other small rodents are highly vulnerable to heat loss during and after the MCAo procedure. The WAAC system provides more precise and controlled Tcore maintenance compared with frequently used induction heating methods in mice undergoing the MCAo stroke model. The improved temperature control should enhance experimental rigor and reduce the number of experimental animals needed.

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An animal's social behaviour both influences and changes in response to its parasites. Here we consider these bidirectional links between host social behaviours and parasite infection, both those that occur from ecological vs evolutionary processes. First, we review how social behaviours of individuals and groups influence ecological patterns of parasite transmission. We then discuss how parasite infection, in turn, can alter host social interactions by changing the behaviour of both infected and uninfected individuals. Together, these ecological feedbacks between social behaviour and parasite infection can result in important epidemiological consequences. Next, we consider the ways in which host social behaviours evolve in response to parasites, highlighting constraints that arise from the need for hosts to maintain benefits of sociality while minimizing fitness costs of parasites. Finally, we consider how host social behaviours shape the population genetic structure of parasites and the evolution of key parasite traits, such as virulence. Overall, these bidirectional relationships between host social behaviours and parasites are an important yet often underappreciated component of population-level disease dynamics and host-parasite coevolution.

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There is large interindividual variability in circadian timing, which is underestimated by mathematical models of the circadian clock. Interindividual differences in timing have traditionally been modeled by changing the intrinsic circadian period, but recent findings reveal an additional potential source of variability: large interindividual differences in light sensitivity. Using an established model of the human circadian clock with real-world light recordings, we investigated whether changes in light sensitivity parameters or intrinsic circadian period could capture variability in circadian timing between and within individuals. Healthy participants (n = 12, aged 18-26 years) underwent continuous light monitoring for 3 weeks (Actiwatch Spectrum). Salivary dim-light melatonin onset (DLMO) was measured each week. Using the recorded light patterns, a sensitivity analysis for predicted DLMO times was performed, varying 3 model parameters within physiological ranges: (1) a parameter determining the steepness of the dose-response curve to light (p), (2) a parameter determining the shape of the phase-response curve to light (K), and (3) the intrinsic circadian period (tau). These parameters were then fitted to obtain optimal predictions of the three DLMO times for each individual. The sensitivity analysis showed that the range of variation in the average predicted DLMO times across participants was 0.65 h for p, 4.28 h for K, and 3.26 h for tau. The default model predicted the DLMO times with a mean absolute error of 1.02 h, whereas fitting all 3 parameters reduced the mean absolute error to 0.28 h. Fitting the parameters independently, we found mean absolute errors of 0.83 h for p, 0.53 h for K, and 0.42 h for tau. Fitting p and K together reduced the mean absolute error to 0.44 h. Light sensitivity parameters captured similar variability in phase compared with intrinsic circadian period, indicating they are viable targets for individualizing circadian phase predictions. Future prospective work is needed that uses measures of light sensitivity to validate this approach.

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AbstractSexually selected ornaments range from highly dynamic traits to those that are fixed during development and relatively static throughout sexual maturity. Ornaments along this continuum differ in the information they provide about the qualities of potential mates, such as their parasite resistance. Dynamic ornaments enable real-time assessment of the bearer's condition: they can reflect an individual's current infection status, or they can reflect resistance to recent infections. Static ornaments, however, are not affected by recent infection but may instead indicate an individual's genetically determined resistance, even in the absence of infection. Given the typically aggregated distribution of parasites among hosts, infection is unlikely to affect the ornaments of the vast majority of individuals in a population: static ornaments may therefore be the more reliable indicators of parasite resistance. To test this hypothesis, we quantified the ornaments of male guppies (Poecilia reticulata) before experimentally infecting them with Gyrodactylus turnbulli. Males with more left-right symmetrical black coloration and those with larger areas of orange coloration, both static ornaments, were more resistant. However, males with more saturated orange coloration, a dynamic ornament, were less resistant. Female guppies often prefer symmetrical males with larger orange ornaments, suggesting that parasite-mediated natural and sexual selection act in concert on these traits.

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The 'social distancing' that occurred in response to the COVID-19 pandemic in humans provides a powerful illustration of the intimate relationship between infectious disease and social behaviour in animals. Indeed, directly transmitted pathogens have long been considered a major cost of group living in humans and other social animals, as well as a driver of the evolution of group size and social behaviour. As the risk and frequency of emerging infectious diseases rise, the ability of social taxa to respond appropriately to changing infectious disease pressures could mean the difference between persistence and extinction. Here, we examine changes in the social behaviour of humans and wildlife in response to infectious diseases and compare these responses to theoretical expectations. We consider constraints on altering social behaviour in the face of emerging diseases, including the lack of behavioural plasticity, environmental limitations and conflicting pressures from the many benefits of group living. We also explore the ways that social animals can minimize the costs of disease-induced changes to sociality and the unique advantages that humans may have in maintaining the benefits of sociality despite social distancing.

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Peroxisomes exist in nearly every cell, oxidizing fats, synthesizing lipids and maintaining redox balance. As the brain ages, multiple pathways are negatively affected, but it is currently unknown if peroxisomal proteins are affected by aging in the brain. While recent studies have investigated a PEX5 homolog in aging C. elegans models and found that it is reduced in aging, it is unclear if PEX5, a mammalian peroxisomal protein that plays a role in peroxisomal homeostasis and degradation, is affected in the aging brain. To answer this question, we first determined the amount of PEX5, in brain homogenates from young (3 months) and aged (26 through 32+ months of age) wild-type mice of both sexes. PEX5 protein was decreased in aged male brains, but this reduction was not significant in female brains. RNAScope and real-time qPCR analyses showed that Pex5 mRNA was also reduced in aged male brain cortices, but not in females. Immunohistochemistry assays of cortical neurons in young and aged male brains showed that the amount of neuronal PEX5 was reduced in aged male brains. Cortical neurons in aged female mice also had reduced PEX5 levels in comparison to younger female mice. In conclusion, total PEX5 levels and Pex5 gene expression both decrease with age in male brains, and neuronal PEX5 levels lower in an age-dependent manner in the cortices of animals of both sexes.

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Neurodevelopment requires precise regulation of gene expression, including post-transcriptional regulatory events such as alternative splicing and mRNA translation. However, translational regulation of specific isoforms during neurodevelopment and the mechanisms behind it remain unknown. Using RNA-seq analysis of mouse neocortical polysomes, here we report translationally repressed and derepressed mRNA isoforms during neocortical neurogenesis whose orthologs include risk genes for neurodevelopmental disorders. We demonstrate that the translation of distinct mRNA isoforms of the RNA binding protein (RBP), Elavl4, in radial glia progenitors and early neurons depends on its alternative 5' UTRs. Furthermore, 5' UTR-driven Elavl4 isoform-specific translation depends on upstream control by another RBP, Celf1. Celf1 regulation of Elavl4 translation dictates development of glutamatergic neurons. Our findings reveal a dynamic interplay between distinct RBPs and alternative 5' UTRs in neuronal development and underscore the risk of post-transcriptional dysregulation in co-occurring neurodevelopmental disorders.

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A large body of research has demonstrated that host-associated microbiota-the archaeal, bacterial, fungal and viral communities residing on and inside organisms-are critical to host health (Cho & Blaser, 2012). Although the vast majority of these studies focus on humans or model organisms in laboratory settings (Pascoe, Hauffe, Marchesi, & Perkins, 2017), they nevertheless provide important conceptual evidence that the disruption of host-associated microbial communities (termed "dysbiosis") among wild animals may reduce host fitness and survival under natural environmental conditions. Among the myriad of environmental factors capable of inducing dysbiosis among wild animals (Trevelline, Fontaine, Hartup, & Kohl, 2019), parasitic infections represent a potentially potent, yet poorly understood, factor influencing microbial community dynamics and animal health. The study by DeCandia et al. in this issue of Molecular Ecology is a rare example of a host-parasite-microbiota interaction that impacts the health, survival and conservation of a threatened wild animal in its natural habitat. Using culture-independent techniques, DeCandia et al. found that the presence of an ectoparasitic mite (Otodectes cynotis) in the ear canal of the Santa Catalina Island fox (Urocyon littoralis catalinae) was associated with significantly reduced ear canal microbial diversity, with the opportunistic pathogen Staphylococcus pseudintermedius dominating the community. These findings suggest that parasite-induced inflammation may contribute to the formation of ceruminous gland tumours in this subspecies of Channel Island fox. As a rare example of a host-parasite-microbiota interaction that may mediate a lethal disease in a population of threatened animals, their study provides an excellent example of how aspects of disease ecology can be integrated into studies of host-associated microbiota to advance conservation science and practice.

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Recent advances in three-dimensional (3D) fluorescence microscopy offer the ability to image the entire vascular network in entire organs, or even whole animals. However, these imaging modalities rely on either endogenous fluorescent reporters or involved immunohistochemistry protocols, as well as optical clearing of the tissue and refractive index matching. Conversely, X-ray-based 3D imaging modalities, such as micro CT, can image non-transparent samples, at high resolution, without requiring complicated or expensive immunolabeling and clearing protocols, or fluorescent reporters. Here, we compared two "homemade" barium-based contrast agents to the field standard, lead-containing Microfil, for micro-computed tomography (micro CT) imaging of the adult mouse cerebrovasculature. The perfusion pressure required for uniform vessel filling was significantly lower with the barium-based contrast agents compared to the polymer-based Microfil. Accordingly, the barium agents showed no evidence of vascular distension or rupture, common problems associated with Microfil. Compellingly, perfusion of an aqueous BaCl2 /gelatin mixture yielded equal or superior visualization of the cerebrovasculature by micro CT compared to Microfil. However, phosphate-containing buffers and fixatives were incompatible with BaCl2 due to the formation of unwanted precipitates. X-ray attenuation of the vessels also decreased overtime, as the BaCl2 appeared to gradually diffuse into surrounding tissues. A second, unique formulation composed of BaSO4 microparticles, generated in-house by mixing BaCl2 and MgSO4 , suffered none of these drawbacks. These microparticles, however, were unable to pass small diameter capillary vessels, conveniently labeling only the arterial cerebrovasculature. In summary, we present an affordable, robust, low pressure, non-toxic, and straightforward methodology for 3D visualization of the cerebrovasculature.

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Understanding the effects of parasites on host behaviour, of host behaviour on parasite infection, and the reciprocal interactions between these processes is vital to improving our understanding of animal behaviour and disease dynamics. However, behaviour and parasite infection are both highly variable within and between individual hosts, and how this variation affects behaviour-parasite feedbacks is poorly understood. For example, it is unclear how an individual's behaviour before infection might change once it becomes infected, or as the infection progresses, and how these changes depend on the host's parasite susceptibility. Here, using the guppy, Poecilia reticulata, and a directly transmitted ectoparasite, Gyrodactylus turnbulli, I show that parasite-induced behavioural plasticity depends on host sex and susceptibility. Among females, time spent shoaling (sociality), a behaviour that increases parasite transmission, did not depend on infection status (infected/not) or susceptibility. By contrast, male sociality in the absence of infection was negatively correlated with susceptibility, suggesting that the most susceptible males use behaviour to avoid infection. However, in late infection, when parasite transmission is most likely, male sociality and susceptibility became positively correlated, suggesting that susceptible males modify their behaviour upon infection potentially to increase transmission and mating opportunities. I discuss the implications of these patterns for disease dynamics.

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