Marcel Eens

Infectious disease emergence in natural systems is driven by complex host–pathogen–environment interactions. Nutritional factors, particularly dietary antioxidants, can modulate physiological states by enhancing immune function and mitigating oxidative damage, but the underlying molecular mechanisms in wildlife remain poorly understood. To bridge this gap, we conducted a transcriptomic analysis of blood samples from both healthy and clinically affected magnificent frigatebirds Fregata magnificens chicks treated with either resveratrol (a plant-derived polyphenol with known antiviral and antioxidant properties) or a placebo. Resveratrol supplementation induced significant gene expression changes, particularly in diseased individuals, where we identified the upregulation of ten key genes in treated sick chicks, including the interferon-stimulated genes (IFI6, OASL2) and immune regulators (SOCS1, PLAC8); two additional transcripts were unannotated. Furthermore, resveratrol treatment was associated with increased expression of DDX60, a potent antiviral factor, and CYGB1, which supports cytoprotection. In contrast, healthy chicks showed fewer differentially expressed genes, primarily associated with metabolism and cellular organization. Collectively, our results reveal a transcriptional signature consistent with dietary antioxidants such as resveratrol acting as active molecular modulators of host defense, rather than simple passive antioxidants, although direct evidence of enhanced antiviral protection (e.g. reduced viral load) remains to be established. This study highlights the utility of transcriptomic approaches to link nutritional ecology with disease dynamics, offering a framework for understanding how dietary quality shapes host defense strategies and population resilience under increasing pathogen pressure.

Urbanisation alters resource availability and exposes wildlife to novel environmental stressors, potentially driving phenotypic divergence. Carotenoid‐based plumage colouration is a condition‐dependent trait linked to dietary carotenoid acquisition and physiological allocation trade‐offs. Although urban populations are often reported to exhibit paler carotenoid colouration than rural populations, these patterns have rarely been tested along continuous fine‐scale urbanisation gradients at a continental scale. We investigated how reflectance parameters of the yellow breast plumage of adult Great Tit ( Parus major ) covary with territory‐scale local imperviousness, used here as a broad descriptor of urban habitat structure, across six European cities. Using 838 adult observations spanning 2005–2024 and sub‐meter‐resolution satellite imagery, we quantified the proportion of impervious surface within 100 m of nest boxes and related this metric to feather carotenoid chroma, brightness and UV chroma. Carotenoid chroma declined significantly with increasing impervious surface cover within breeding territories across Europe, corresponding to an expected decrease of 0.053 chroma units across the observed 0%–88% imperviousness gradient. This relationship remained robust across bootstrap resampling, leave‐one‐city‐out analyses and models controlling for among‐city variation in mean carotenoid chroma. Older individuals exhibited higher carotenoid chroma than yearlings, while males tended to be more chromatic and brighter than females. Impervious surface cover was not associated with feather brightness or UV chroma, indicating that urban habitat structure is linked specifically to carotenoid pigment deposition rather than feather structural properties and overall quality. Because carotenoid‐based colouration depends on dietary intake, higher levels of impervious cover and reduced vegetation may reflect lower availability of carotenoid‐rich resources in urban territories, although imperviousness should be interpreted as a multifactorial habitat descriptor rather than a direct mechanistic proxy. Our study provides the first continent‐scale evidence that carotenoid‐based colouration declines along a continuous urbanisation gradient. These findings identify plumage carotenoid chroma as a phenotypic correlate of local imperviousness within European cities and highlight the importance of fine‐scale habitat characterisation for understanding phenotypic responses to urbanisation. Future studies should test the mechanistic links between territory‐scale imperviousness, diet composition, pollutant exposure, physiological condition and fitness.

The extensive production and use of per- and polyfluoroalkyl substances (PFAS) over recent decades have resulted in their pervasive distribution in environmental compartments worldwide. PFAS concentrations in soil and biota near fluorochemical manufacturing facilities tend to be typically higher near hotspots, which suggests that the consumption of home-produced foods near such hotspots most likely results in higher human exposure. One prominent European hotspot is located near the 3M fluorochemical production facility in Zwijndrecht (Belgium), where the relative contributions of different exposure pathways remain insufficiently characterised. This study therefore aimed to assess the PFAS concentrations and compositional profiles in serum, dwellings and gardens of teenagers residing near this hotspot. Serum samples from teenagers, along with multiple environmental matrices (i.e., soil, compost, vegetables/fruits/nuts, chicken eggs, rainwater and indoor house dust) were analysed for 21 selected PFAS. Additionally, potential determinants of PFAS occurrence and distribution across matrices were investigated using detailed questionnaire data. We found perfluorooctane sulfonic acid (PFOS) to be the predominant compound in both soil and serum, while perfluorobutanoic acid (PFBA) was most dominant in rainwater, compost, house dust and pods. Perfluorobutane sulfonic acid (PFBS) was most abundant in fruits and chicken eggs, while perfluorododecanoic acid (PFDoDA) was predominant in rooting vegetables and nuts. N-methylperfluorooctane sulfonamidoacetic acid (MePFOSAA) was the dominant compound in fruiting, stem, and leafy vegetables. These results indicate differences in accumulation pathways among the different media and/or differences in affinities of different PFAS in the matrices. Additionally, several environmental and behavioural factors were identified as determinants for PFAS in soil, compost, tree fruits, fruiting vegetables, chicken eggs and house dust, providing insight into potential drivers of exposure variability. The most important factors were related to the soil characteristics, the composting of grass and weeds, the chicken feed (i.e., bread, commercial feed), the type and frequency of ventilation and the frequency of cleaning.

The capacity for birds to adjust their breeding time to variation in spring temperature via plasticity is crucial for insectivorous passerines in temperate areas, particularly in a context of climate disruptions. Recent studies suggested that phenological plasticity varies in response to environmental change via urbanization. We investigated the effects of urbanization on laying date, its phenotypic plasticity in response to spring temperature, and the between-individual variation in laying date, using data from five long-term studies of European great tits, Parus major, in forest and urban areas. First, we compared laying phenology and its plasticity in response to spring temperature between urban and forest populations. We confirmed that birds lay eggs earlier in urban environments in four populations and revealed reduced phenological plasticity in more urbanized environments in two populations. Additionally, we demonstrated greater between-individual variation in laying date in two urban areas. Second, we focused on urban populations only, and showed that the proportion of impervious surface area had little effect on the laying date. Overall, urbanization was associated with earlier breeding and less plasticity, although the strength of these associations varied among cities, likely owing to variation in the intensity of urbanization, landscape connectivity and habitat composition.

The long-standing view that bonobos ( Pan paniscus ) are peaceful while chimpanzees ( Pan troglodytes ) are aggressive has shaped our understanding of primate and human social evolution. However, recent observations from the wild challenge this dichotomy, warranting standardized comparative analyses of aggression in the Pan species. Here, we examined aggressive interactions across 22 zoo-housed groups of chimpanzees ( N = 9 groups, 101 individuals) and bonobos ( N = 13 groups, 88 individuals) using Bayesian social network analysis. We find no species differences in overall or contact aggression rates, accounting for group size and sex ratio. However, aggression patterns diverge by sex: Bonobos exhibit higher female-to-male aggression, while chimpanzees show the reverse. Notably, absolute aggression rates varied substantially between groups within each species, reinforcing recent evidence on group-specific social structures in Pan . These findings challenge the traditional aggression dichotomy between bonobos and chimpanzees and provide insights into the evolutionary dynamics of social conflict strategies in great apes, including humans.

Sound production is widespread across the animal kingdom and can take many forms and serve various functions. A hissing sound is a non-vocal acoustic signal produced by forced air ventilation and is hypothesized to be a behavioural symplesiomorphy in Amniota. Yet, hissing sounds are typically associated with reptiles and have received comparably little research attention in birds. Here, we identified at least 86 families within 34 avian orders in which members produced hissing sounds. Despite being widespread, almost nothing is currently known about the mechanism(s) of avian hissing sound production. Functions of hissing signals were divided into broad categories based on the social/behavioural context in which they are typically expressed and most evidence pointed towards a main role in threat/defence displays towards predators. Yet, interesting examples exist where avian hissing signals are involved in agonistic interactions, parent-offspring communication, sibling competition, mating displays, pair communication and heterospecific eavesdropping. Our review also emphasizes that research on hissing sounds regarding individual variation, acoustic individuality, geographic variation and fitness consequences is still in its infancy. Overall, hissing sounds are widespread and can be involved in communication in many crucial aspects of avian life, thereby spanning various contemporary disciplines in behavioural and evolutionary ecology.