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In cooperatively breeding species, group members may derive multiple benefits from helping to raise other individuals' offspring, yet not all individuals do so. In this study, we tested predictions from the "kin selection", "pay-to-stay", "group augmentation" and "skills" hypotheses, to explain why group members feed nestlings of breeding placid greenbuls (Phyllastrephus placidus). In our study population, about 70% of the breeding pairs were accompanied by subordinates, and in 60% of these cases at least one subordinate helped in provisioning nestlings. In total, 80% of the subordinates were related to one or both breeders. In accordance with the "kin selection" hypothesis, and contrary to the "pay-to-stay" hypothesis, all the helpers were first-order kin of the breeding female (although relatedness to the breeding male did not explain variation in helping) and the presence of helpers was associated with increased survival of the breeding pair. However, the propensity to help varied among group members, as 46% of group members related to the breeding female did not feed nestlings. Younger helpers fed offspring more often than older ones, supporting the "skills" and "group augmentation" hypotheses. However, support for the "group augmentation" hypothesis was mixed since subordinate sex and group size did not explain additional variation in helping propensity and effort. We argue that in addition to indirect and direct benefits, also the costs of helping as well as other types of helping aside from provisioning must be considered to better understand variation in helping behavior. Relatedness is thought to be an important factor explaining helping at the nest by non-breeding group members. We show that placid greenbul helpers are always related to the breeding females, supporting this view. However, many related groups members never helped suggesting that other factors shape helping decision in this species.

Females are predicted to adjust their reproductive investment to optimize the trade-off between current and future reproduction. In many cooperatively breeding birds, females have been shown to reduce their investment both pre- and posthatching in response to the presence of food-provisioning helpers. However, in species where not all group members help during the posthatching stage, it is currently unclear to which social cues (i.e. group size versus number of helpers) females should tune their investment. Here, we used the cooperatively breeding placid greenbul, Phyllastrephus placidus, as a model species to examine whether and how group size and number of helpers affect female investment in eggs and food provisioning. We found that females used a contrasting strategy pre- and posthatching in response to different social cues: they laid larger eggs in larger groups while reducing their feeding rate when assisted by more helpers. We also found that fledging success increased with group size and that nestlings raised in groups with helpers fledged with longer wings but found no relation between condition of the young and number of helpers. Since the perceived contrasting investment strategies may have several underlying causes, we conclude that predicting the influence of social conditions on maternal investment may be more challenging than previously believed. (c) 2023 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Many studies have investigated how spring temperature affects laying dates and how this in turn affects the synchrony between nestling food demands and the insect food peak that follows tree budburst. While there is strong evidence that temperature itself acts as a cue for this plasticity in annual timing, the exact nature of the cue and response remains to be elucidated. Here we use long-term data on Great and Blue Tits and an unprecedented dataset on the location and phenology of 1396 trees to investigate whether small-scale variation in laying date can be explained by local tree phenology, and/or by tree species composition around nestboxes. Individual trees maintained their relative timing of budburst between years, while differences among tree species were more variable between springs. Contrary to expectation, we found no relation between first-egg dates and average budburst date at different distances around the nestbox. This can at least partly be explained by the very low degree of spatial autocorrelation in tree budburst. We did find an effect of local tree composition whereby Blue Tits, but not Great Tits, laid earlier in nestboxes surrounded by more oaks and fewer beeches. Although Blue Tit nest failure rate was higher in territories with more beech trees, independently of laying date, we found no evidence for preferential occupation of oak-dominated territories. Thus although we found some evidence for fine-scale effects of tree species on timing of breeding, the underlying mechanism remains unclear.

Urbanization has been shown to strongly affect community composition of various taxa with potentially strong shifts in ecological interactions, including those between hosts and parasites. We investigated the effect of urbanization on the composition of arthropods in nests of great tits in Flanders, Belgium. These nests contain taxonomically and functionally diverse arthropod communities including parasites, predators, detritivores and accidental commensals. Using a standardized hierarchical sampling design with subplots (200 m x 200 m) nested in plots (3 km x 3 km) of varying urbanization levels, we collected arthropods from nests of resident great tits after the young had fledged. Arthropods were extracted, identified to Primary Taxonomical Groups (PTG) and counted. Using generalized linear mixed models (GLMMs) we found diverging effects of urbanization on PTG occurrences and abundances at various levels, but we did not find an overall signal in arthropod diversity or richness. Also, visual inspection of non-metric multidimensional scaling (NMDS) plots did not reveal any community differences between urbanization levels at plot or subplot scales. Land use and environmental variables at different distances around nestboxes did not contribute much to the variation between communities. Our results indicate that arthropod nestbox communities are generally not adversely affected by urbanization, and even city gardens and parks harbor comparable communities to forests and suburban areas. We thus found no evidence for a parasite release effect due to urbanization, nor an increased risk of parasitism in human-dominated environments.

Sustainable land-use management must account for the potential trade-offs between biodiversity conservation, productive land uses and ecosystem services. In this study, we used Marxan with Zones to generate land use plans that optimize conservation, farming and forestry land uses to reach biodiversity targets while minimizing the opportunity cost for local communities in an inhabited but data-poor National Park in the Andes of Bolivia. Based on six alternative land-use plans, we identified the synergies and trade-offs between the biodiversity benefits achieved in the different plans and the delivery of four locally important water-related ecosystem services modeled with the web-based tool AguAAndes. Although we find synergies between the conservation of high altitude Polylepis woodlands and their associated avifauna and three of the ecosystem services investigated, soil erosion levels were actually higher in scenarios with higher achieved biodiversity benefits. Our study shows how systematic conservation planning and ecosystem service delivery modelling can be used to solve land-use conflicts and identify trade-offs between biodiversity conservation and ecosystem services in a data-poor tropical area.

The biotic and abiotic environments in bird nests change during the nesting cycle as eggs are laid and incubated and nestlings develop and eventually fledge. Nest-arthropod communities have been studied for many bird species and are commonly sampled after young fledge. However, the population dynamics of arthropods in nests are expected to vary over the nesting cycle as a result of the changing nest environment, in symphony with arthropod life cycles and generation times. Few investigators have examined nest arthropod communities at different stages of the breeding period. We collected nests of Great Tits (Parus major) at the egg stage, nestling stage, and after fledging, and extracted nest arthropods using Berlese funnels and identified them to Primary Taxonomic Groups (PTGs). Total arthropod abundance, as well as abundance of fleas, parasitic mites, and adult predatory beetles, was higher during the nestling stage than after fledging. The abundance of beetle mites decreased from the egg stage to fledging, whereas larval predatory beetles and scavenger flies increased. Thus, our results demonstrate important changes in overall abundance, but also in the trophic structure of nest arthropod communities during the nesting cycle. Our results also suggest that nests collected after fledging may give biased information on the abundance of parasites, or nest-arthropod communities in general, during the nestling stage.

Identifying the environmental drivers of variation in fitness-related traits is a central objective in ecology and evolutionary biology. Temporal fluctuations of these environmental drivers are often synchronized at large spatial scales. Yet, whether synchronous environmental conditions can generate spatial synchrony in fitness-related trait values (i.e., correlated temporal trait fluctuations across populations) is poorly understood. Using data from long-term monitored populations of blue tits (Cyanistes caeruleus, n = 31), great tits (Parus major, n = 35), and pied flycatchers (Ficedula hypoleuca, n = 20) across Europe, we assessed the influence of two local climatic variables (mean temperature and mean precipitation in February–May) on spatial synchrony in three fitness-related traits: laying date, clutch size, and fledgling number. We found a high degree of spatial synchrony in laying date but a lower degree in clutch size and fledgling number for each species. Temperature strongly influenced spatial synchrony in laying date for resident blue tits and great tits but not for migratory pied flycatchers. This is a relevant finding in the context of environmental impacts on populations because spatial synchrony in fitness-related trait values among populations may influence fluctuations in vital rates or population abundances. If environmentally induced spatial synchrony in fitness-related traits increases the spatial synchrony in vital rates or population abundances, this will ultimately increase the risk of extinction for populations and species. Assessing how environmental conditions influence spatiotemporal variation in trait values improves our mechanistic understanding of environmental impacts on populations. birds, climate, clutch size, comparative analysis, fitness-related traits, fledgling number, phenology, spatial synchrony, timing of breeding, weather

The distribution of ticks in the Ixodes ricinus species complex is partly driven by climate, with temperature and relative humidity affecting survival. These variables are driven by macroclimate, but vary locally due to microclimate buffering. This buffering has been suggested to be one of the driving forces behind variation in tick survival and density in time and space. In order to understand the role of the herb layer with respect to this variation, we deployed I. ricinus within an existing experimental setup studying the response of forest under -storey to micrometeorological changes. This allowed for the analysis of both direct effects of warming on tick survival in controlled field conditions, as well as indirect effects through changes in herb layer biomass. Herb layer biomass estimates were observed to be higher in plots that had been experimentally warmed, with a trend towards higher survival in these warmed plots. This marginal increase in survival rate may be due to increased microclimate buffering. Comparing our results to literature implies that canopy and shrub layer vegetation have a larger effect on climate buffering, and therefore also on tick survival. Since the herb layer biomass is expected to increase due to global warming and increased frequency of disturbance-induced canopy gaps, survival in forested habitats may increase in the future. This would increase the difference in survival compared to that in open habitats.

Wild birds are frequently exposed to the zoonotic tick-borne bacteria Borrelia burgdorferi sensu lato (s.l.), and some bird species act as reservoirs for some Borrelia genospecies. Studying the tropism of Borrelia in the host, how it is sequestered in different organs, and whether it is maintained in circulation and/or in the host's skin is important to understand pathogenicity, infectivity to vector ticks and reservoir competency.We evaluated tissue dissemination of Borrelia in blackbirds (Turdus merula) and great tits (Parus major), naturally and experimentally infected with Borrelia genospecies from enzootic foci. We collected both minimally invasive biological samples (feathers, skin biopsies and blood) and skin, joint, brain and visceral tissues from necropsied birds. Infectiousness of the host was evaluated through xenodiagnoses and infection rates in fed and moulted ticks. Skin biopsies were the most reliable method for assessing avian hosts' Borrelia infectiousness, which was supported by the agreement of infection status results obtained from the analysis of chin and lore skin samples from necropsied birds and of their xenodiagnostic ticks, including a significant correlation between the estimated concentration of Borrelia genome copies in the skin and the Borrelia infection rate in the xenodiagnostic ticks. This confirms a dermatropism of Borrelia garinii, B. valaisiana and B. turdi in its avian hosts. However, time elapsed from exposure to Borrelia and interaction between host species and Borrelia genospecies may affect the reliability of skin biopsies. The blood was not useful to assess infectiousness of birds, even during the period of expected maximum spirochetaemia. From the tissues sampled (foot joint, liver, spleen, heart, kidney, gut and brain), Borrelia was detected only in the gut, which could be related with infection mode, genospecies competition, genospecies-specific seasonality and/or excretion processes. This study received financial support from Fundação para a Ciência e a Tecnologia by the strategic program of MARE (MARE - UID/MAR/04292/2019), the fellowship to Ana Cláudia Norte (SFRH/BPD/108197/2015) and from the Portuguese National Institute of Health Doutor Ricardo Jorge. Dieter Heylen is funded by the Marie Sklodowska-Curie Actions (EU-Horizon 2020, Individual Global Fellowship, project no. 799609), the Fund for Scientific Research – Flanders (FWO) and the Bill & Melinda Gates Foundation. info:eu-repo/semantics/publishedVersion

Conspecific density and animal personality (consistent among‐individual differences in behavior) may both play an important role in disease ecology. Nevertheless, both factors have rarely been studied together but may provide insightful information in understanding pathogen transmission dynamics. In this study, we investigated how both personality and density affect viral infections both direct and indirectly, using the multimammate mice (Mastomys natalensis) and Morogoro arenavirus (MORV) as a model system. Using a replicated semi‐natural experiment, we found a positive correlation between MORV antibody presence and density, suggesting that MORV infection is density‐dependent. Surprisingly, slower explorers were more likely to have antibodies against MORV compared to highly explorative individuals. However, exploration was positively correlated with density which may suggest a negative, indirect effect of density on MORV infection. We have shown here that in order to better understand disease ecology, both personality and density should be taken into account., Most studies concerning personality and its effect on parasitic or viral infection probability found that highly explorative individuals were more likely to acquire infection. We have found the opposite pattern in Mastomys natalensis, where individuals with antibodies against the Morogoro virus (MORVab) were significantly less explorative than individuals without antibodies against this virus.

Individual variation in behaviour can contribute to the heterogeneous distribution of parasites among hosts for example by affecting the probability of encountering infective stages (larvae). Here, we investigated the relationship between host boldness/exploration tendency and gastro-intestinal helminth infection in invasive Eastern grey squirrels (Sciurus carolinensis). We used direct helminth counts, data rarely available in host-parasite studies that often used less reliable indirect estimates of infection. We predicted that bolder animals with a strong exploration tendency will have higher parasite load than shy, less explorative hosts. We examined two parameters of parasite infection: infection status and intensity of infection. Individual personality of 207 grey squirrels was assessed by capture-mark-recapture (CMR), calculating the trappability and trap diversity indices as estimates of boldness and exploration, respectively. Since both indices were strongly correlated, we used PCA to derive a single score (first component) which had a high value for bold, exploring animals. At the end of the study, 77 individuals were euthanized and gastro-intestinal helminths were identified and counted. Overall 73% of grey squirrels were infected by Strongyloides robustus with the intensity of infection varying from 1 to 86 worms (mean ± SE = 10.7 ± 2.1 helminths per host). We found that bolder, more explorative animals were more likely to be infected by S. robustus. However, host personality was not related to parasite intensity, which was instead positively associated with host body mass. Our results confirm that differences in personality-related host behaviour can influence the distribution of infections within host populations and stimulate further questions on whether such personality-parasite relationships may affect the invasion process.

Heterogeneous selection is often proposed as a key mechanism maintaining repeatable behavioral variation ("animal personality") in wild populations. Previous studies largely focused on temporal variation in selection within single populations. The relative importance of spatial versus temporal variation remains unexplored, despite these processes having distinct effects on local adaptation. Using data from >3,500 great tits (Parus major) and 35 nest box plots situated within five West-European populations monitored over 4 to 18 y, we show that selection on exploration behavior varies primarily spatially, across populations, and study plots within populations. Exploration was, simultaneously, selectively neutral in the average population and year. These findings imply that spatial variation in selection may represent a primary mechanism maintaining animal personalities, likely promoting the evolution of local adaptation, phenotype-dependent dispersal, and nonrandom settlement. Selection also varied within populations among years, which may counteract local adaptation. Our study underlines the importance of combining multiple spatiotemporal scales in the study of behavioral adaptation.

Background: Variation in parasite burdens among hosts is typically related to differences in adaptive immunity. Comprehension of underlying mechanisms is hence necessary to gain better insights into endemic transmission cycles. Here we investigate whether wild songbirds that have never been exposed to ticks develop adaptive humoral immunity against endemic Ixodes ricinus ticks. Methods: Blue tits were exposed three times in succession to wild Ixodes ricinus ticks. For each infestation, serum samples were obtained. An enzyme-linked immunosorbent assay was developed, using tick salivary antigens, in order to quantify the bird’s IgY response against ticks. In addition, at every sampling occasion the birds’ body weight (corrected for body size) and haematocrit level was determined. Results: Individual IgY levels against the ticks’ salivary proteins increased over three consecutive tick infestations, and large among-individual variation was observed. The responses were specifically directed against I. ricinus; cross-reactivity against the congeneric tree-hole tick Ixodes arboricola was negligibly low. IgY responses did not impinge on tick feeding success (engorgement weight and attachment success). Yet, those birds with the highest immune responses were more capable to reduce the acute harm (blood depletions) by compensating erythrocyte loss. Furthermore, at the end of the experiment, these birds had gained more body weight than birds with lower IgY levels. Conclusions: Latter observations can be considered as an effect of host quality and/or tolerance mechanisms. Birds anticipate the (future) costs of the activation of the immune system by ticks and/or ongoing tick-borne pathogen infections. Furthermore, although unsuccessful against tick feeding, the IgY responses may indirectly protect birds against tick-borne disease by acting against salivary protein secretions on which pathogens rely for transmission. Grant Information: This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No [799609], (project ECODIS). DH is also funded by the Fund for Scientific Research – Flanders (FWO). BB is funded by the European Community Action Scheme for the Mobility of University Students Programme. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Open Access

The pace-of-life syndrome (POLS) theory provides an evolutionary explanation for the existence of consistent among-individual variation in behaviour, or animal personality. Herein, individuals with a fast lifestyle are considered to be bolder and should take more risks resulting in a lower life expectancy compared to shyer individuals with a slower lifestyle. However, this assumption depends on the levels of intra-specific competition that the individuals experience which has rarely been tested in species that experience large changes in competition on a very short time scale. We used the multimammate mice (Mastomys natalensis) as a model system to study the POLS assumption by investigating the effects of two personality traits (exploration and stress-sensitivity) on survival, maturation (a proxy for reproductive investment) and recapture probability during one population cycle (N

The pace-of-life syndrome (POLS) theory provides an evolutionary explanation for the existence of consistent among-individual variation in behaviour, or animal personality. Herein, individuals with a fast lifestyle are considered to be bolder and should take more risks resulting in a lower life expectancy compared to shyer individuals with a slower lifestyle. However, this assumption depends on the levels of intra-specific competition that the individuals experience which has rarely been tested in species that experience large changes in competition on a very short time scale. We used the multimammate mice (Mastomys natalensis) as a model system to study the POLS assumption by investigating the effects of two personality traits (exploration and stress-sensitivity) on survival, maturation (a proxy for reproductive investment) and recapture probability during one population cycle (Nindividuals = 201). Such a cycle consists of two phases in which the levels of intra-specific competition vary drastically. We found that only one personality trait, namely stress-sensitivity, had a negative effect on both survival and recapture probability but none of them affected maturation. This suggests that less stress-sensitive individuals take more risks in the wild and have a higher survival probability compared to high stress-sensitive individuals. However, the effect of personality on survival was only present during the population decrease phase, when the levels of intra-specific competition are high due to a scarcity of food. This suggests that seasonal changes in competition might be important in the evolution and maintenance of animal personalities in species whose population dynamics have a clear seasonal component.

Polylepis forests are endemic to the high‐Andes, with trees characterized by multi‐layered, exfoliating bark‐providing protection against harsh, high‐elevation conditions, both for individual trees and the wide array of organisms dependent on them. However, Polylepis habitat has suffered severe human‐induced land conversion and currently mainly occurs as fragmented remnants only. Here, we studied the effects of fragment size on local ambient temperature and on biomass of bark and its bark‐dwelling arthropods. We did so by comparing multiple samples at the edge and interior of both large and small fragments, while also accounting for branch size, tree width, and tree structure. Because arthropod biomass is likely to impact higher trophic levels, we also studied abundance and foraging behavior of two bird species specialized on Polylepis forest. We show that arthropod biomass was relatively higher in wider, larger trees, which were preferred for foraging by both bird species. Moreover, we show that small forest fragments are not only environmentally less buffered but are also characterized by lower amounts of bark and lower densities of bark‐dwelling arthropods than larger fragments. Our study highlights the conservation value of large trees. Also, we advise it is now timely to test to what degree restoration efforts to increase fragment size could mitigate the negative effects of reduced arthropod biomass for higher trophic levels of endemic specialist insectivores.

It remains poorly understood how effects of anthropogenic activity, such as large-scale habitat fragmentation, impact sociality in animals. In cooperatively breeding species, groups are mostly formed through delayed offspring dispersal, and habitat fragmentation can affect this process in two opposite directions. Increased habitat isolation may increase dispersal costs, promoting delayed dispersal. Alternatively, reduced patch size and quality may decrease benefits of philopatry, promoting dispersal. Here, we test both predictions in a cooperatively breeding bird (placid greenbul, Phyllastrephus placidus ) from an Afrotropical cloud forest archipelago. Males born in fragmented forest dispersed about 1 year earlier than those born in continuous forest. Contrary to females, males also started to reproduce earlier and mostly settled within their natal patch. Females only rarely delayed their dispersal for more than 1 year, both in fragmented and continuous forests. Our results suggest that early male dispersal and reproduction is jointly driven by a decrease in the value of the natal territory and an increase in local breeding opportunities in fragmented forest. While plasticity in dispersal strategies of cooperative breeders in response to anthropogenic change is believed to optimize reproduction-survival trade-offs, to what extent it shapes the ability of species to respond to rapid environmental change remains to be studied.

The phenology of many species shows strong sensitivity to climate change; however, with few large scale intra-specific studies it is unclear how such sensitivity varies over a species’ range. We document large intra-specific variation in phenological sensitivity to temperature using laying date information from 67 populations of two European songbirds covering a large part of their breeding range. Populations inhabiting deciduous habitats showed stronger phenological sensitivity compared with those in evergreen and mixed habitats. Strikingly, however, the lowest sensitivity was seen in populations that had experienced the greatest change in climate. Therefore, we predict that the strongest phenological advancement will not occur in those populations with the highest sensitivity. Our results show that to effectively assess the impact of climate change on phenology across a species range it will be necessary to account for intra-specific variation in phenological sensitivity, climate change exposure, and the ecological characteristics of a population.

Consistent among-individual variation in behavior, or animal personality, is present in a wide variety of species. This behavioral variation is maintained by both genetic and environmental factors. Parental effects are a special case of environmental variation and are expected to evolve in populations experiencing large fluctuations in their environment. They represent a non-genetic pathway by which parents can transmit information to their offspring, by modulating their personality. While it is expected that parental effects contribute to the observed personality variation, this has rarely been studied in wild populations. We used the multimammate mouse Mastomys natalensis as a model system to investigate the potential effects of maternal personality on offspring behavior. We did this by repeatedly recording the behavior of individually housed juveniles which were born and raised in the lab from wild caught females. A linear correlation, between mother and offspring in behavior, would be expected when the personality is only affected by additive genetic variation, while a more complex relationship would suggests the presence of maternal effects. We found that the personality of the mother predicted the behavior of their offspring in a non-linear pattern. Exploration behavior of mother and offspring was positively correlated, but only for slow and average exploring mothers, while this correlation became negative for fast exploring mothers. This may suggests that early maternal effects could affect personality in juvenile M. natalensis, potentially due to density-dependent and negative frequency-dependent mechanisms, and therefore contribute to the maintenance of personality variation.

Human activities impact upon natural habitats used by birds for breeding and foraging, and lead to changes in the composition and spatial distribution of predator communities, mainly through loss, fragmentation and disturbance of formerly pristine habitat. Yet possible fitness consequences of such changes through impacts on bird nest‐site selection remain poorly known. Here we study nest‐site selection and reproductive success of Placid Greenbuls Phyllastrephus placidus in the Taita Hills, southeast Kenya. We show that habitat features associated with nest‐site selection by this insectivorous, open‐cup‐nesting bird species vary among forest fragments that are exposed to different levels of habitat disturbance. Such differences in sites selected for breeding result from a plastic response to fragment‐specific conditions or may be driven by fragment‐specific variation in the distribution and availability of certain habitat features. Given the overall high nest predation rates in our study area, we expected variation in nest‐site selection to correlate with reproductive success and nestling condition, but detected no such relationship. Because predator density and nest predation rates may vary strongly in space and time, a better understanding of spatio‐temporal variation in predator communities is needed to assess the possible adaptive value of nest‐site selection strategies for reducing the high predation rates that are typical for this and many other open‐cup‐nesting tropical passerines.

Unique evolutionary potential could be lost when a population goes extinct or when individuals are translocated to other existing populations. Therefore, in order to identify priorities and to predict the efficiency and consequences of conservation actions, information is needed on the genetic structure of natural populations. In the urbanized and diverse landscapes of Flanders, Belgium, natterjack toad (Epidalea calamita) populations have been declining over the last decades. Therefore, this species is subjected to a wide range of different types of conservation measures (e.g. habitat management, corridor development, translocations). However, more information is needed on its genetic population structure. In this study, we sampled egg clutches from six populations and studied their genetic structure with six microsatellite markers. In total, 184 samples from 99 different egg strings were genotyped. Observed heterozygosity was generally high, even for the small and isolated populations (overall mean HO = 0.43). The weak clustering by the Bayesian analyses (STRUCTURE, Adegenet and BAPS) does not allow us to make strong conclusions on the population structure. However, the significant ΦST values between the populations underline the importance of genetic information when conservation priorities are discussed. Unique evolutionary potential could be lost when one or more natterjack toad populations would go extinct, and translocation of individuals to other existing populations should be considered with caution.

The increasing urbanization process is hypothesized to drastically alter (semi-)natural environments with a concomitant major decline in species abundance and diversity. Yet, studies on this effect of urbanization, and the spatial scale at which it acts, are at present inconclusive due to the large heterogeneity in taxonomic groups and spatial scales at which this relationship has been investigated among studies. Comprehensive studies analysing this relationship across multiple animal groups and at multiple spatial scales are rare, hampering the assessment of how biodiversity generally responds to urbanization. We studied aquatic (cladocerans), limno-terrestrial (bdelloid rotifers) and terrestrial (butterflies, ground beetles, ground- and web spiders, macro-moths, orthopterans and snails) invertebrate groups using a hierarchical spatial design, wherein three local-scale (200 m x 200 m) urbanization levels were repeatedly sampled across three landscape-scale (3 km x 3 km) urbanization levels. We tested for local and landscape urbanization effects on abundance and species richness of each group, whereby total richness was partitioned into the average richness of local communities and the richness due to variation among local communities. Abundances of the terrestrial active dispersers declined in response to local urbanization, with reductions up to 85% for butterflies, while passive dispersers did not show any clear trend. Species richness also declined with increasing levels of urbanization, but responses were highly heterogeneous among the different groups with respect to the richness component and the spatial scale at which urbanization impacts richness. Depending on the group, species richness declined due to biotic homogenization and/or local species loss. This resulted in an overall decrease in total richness across groups in urban areas. These results provide strong support to the general negative impact of urbanization on abundance and species richness within habitat patches and highlight the importance of considering multiple spatial scales and taxa to assess the impacts of urbanization on biodiversity. Belgian Science Policy Office, Grant/Award Number: P07/4; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico, Grant/Award Number: 45968/2012-1 Piano, E (reprint author), Univ Turin, Dept Life Sci & Syst Biol, Turin, Italy. elena.piano@unito.it

Humans fundamentally affect dispersal, directly by transporting individuals and indirectly by altering landscapes and natural vectors. This human-mediated dispersal (HMD) modifies long-distance dispersal, changes dispersal paths, and overall benefits certain species or genotypes while disadvantaging others. HMD is leading to radical changes in the structure and functioning of spatial networks, which are likely to intensify as human activities increase in scope and extent. Here, we provide an overview to guide research into HMD and the resulting rewiring of spatial networks, making predictions about the ecological and evolutionary consequences and how these vary according to spatial scale and the traits of species. Future research should consider HMD holistically, assessing the range of direct and indirect processes to understand the complex impacts on eco-evolutionary dynamics.

An increasing number of studies have investigated the consequences of biodiversity loss for the occurrence of vector-borne diseases such as Lyme borreliosis, the most common tick-borne disease in the northern hemisphere. As host species differ in their ability to transmit the Lyme borreliosis bacteria Borrelia burgdorferi s.l. to ticks, increased host diversity can decrease disease prevalence by increasing the proportion of dilution hosts, host species that transmit pathogens less efficiently. Previous research shows that Lyme borreliosis risk differs between forest types and suggests that a higher diversity of host species might dilute the contribution of small rodents to infect ticks with B. afzelii, a common Borrelia genospecies. However, empirical evidence for a dilution effect in Europe is largely lacking. We tested the dilution effect hypothesis in 19 Belgian forest stands of different forest types along a diversity gradient. We used empirical data and a Bayesian belief network to investigate the impact of the proportion of dilution hosts on the density of ticks infected with B. afzelii, and identified the key drivers determining the density of infected ticks, which is a measure of human infection risk. Densities of ticks and B. afzelii infection prevalence differed between forest types, but the model indicated that the density of infected ticks is hardly affected by dilution. The most important variables explaining variability in disease risk were related to the density of ticks. Combining empirical data with a model-based approach supported decision making to reduce tick-borne disease risk. We found a low probability of a dilution effect for Lyme borreliosis in a north-western European context. We emphasize that under these circumstances, Lyme borreliosis prevention should rather aim at reducing tick-human contact rate instead of attempting to increase the proportion of dilution hosts.

Urbanisation represents one of the most radical forms of terrestrial land use change and has been shown to lead to alterations in ecosystem functioning and community dynamics and changes in individual phenotypic traits. While the recent surge in microbiome studies has brought about a paradigm shift by which individuals cannot truly be considered independently of the bacterial communities they host, the role of gut microbiota in organismal response to human-induced environmental change is still scarcely studied. Here, we applied a metabarcoding approach to examine the impact of urbanisation on the gut microbiota of Passer domesticus. We found urbanisation to be associated to lower microbiota species diversity, modifications in taxonomic composition and community structure, and changes in functional composition. The strength of these relationships, however, depended on the spatial scale and season at which they were considered. Such spatio-temporal effect suggests that urbanisation may dampen the natural seasonal variation of the gut microbiota observed in more pristine habitats, potentially influencing the fitness of urban organisms. Our results hence shed light on a hitherto little considered perspective, i.e. that the negative effects of urbanisation on city-dwelling organisms may extend to their microbiomes, causing potential dysbioses.

Dispersal is a process of central importance for the ecological and evolutionary dynamics of populations and communities, because of its diverse consequences for gene flow and demography. It is subject to evolutionary change, which begs the question, what is the genetic basis of this potentially complex trait? To address this question, we (i) review the empirical literature on the genetic basis of dispersal, (ii) explore how theoretical investigations of the evolution of dispersal have represented the genetics of dispersal, and (iii) discuss how the genetic basis of dispersal influences theoretical predictions of the evolution of dispersal and potential consequences. Dispersal has a detectable genetic basis in many organisms, from bacteria to plants and animals. Generally, there is evidence for significant genetic variation for dispersal or dispersal-related phenotypes or evidence for the micro-evolution of dispersal in natural populations. Dispersal is typically the outcome of several interacting traits, and this complexity is reflected in its genetic architecture: while some genes of moderate to large effect can influence certain aspects of dispersal, dispersal traits are typically polygenic. Correlations among dispersal traits as well as between dispersal traits and other traits under selection are common, and the genetic basis of dispersal can be highly environment-dependent. By contrast, models have historically considered a highly simplified genetic architecture of dispersal. It is only recently that models have started to consider multiple loci influencing dispersal, as well as non-additive effects such as dominance and epistasis, showing that the genetic basis of dispersal can influence evolutionary rates and outcomes, especially under non-equilibrium conditions. For example, the number of loci controlling dispersal can influence projected rates of dispersal evolution during range shifts and corresponding demographic impacts. Incorporating more realism in the genetic architecture of dispersal is thus necessary to enable models to move beyond the purely theoretical towards making more useful predictions of evolutionary and ecological dynamics under current and future environmental conditions. To inform these advances, empirical studies need to answer outstanding questions concerning whether specific genes underlie dispersal variation, the genetic architecture of context-dependent dispersal phenotypes and behaviours, and correlations among dispersal and other traits.

Candidatus Rickettsia vini was originally detected in Ixodes arboricola ticks from Spain, and subsequently reported from several other Western Palearctic countries including Belgium. Recently, the bacterium was isolated in mammalian (Vero) cell culture from macerated male I. arboricola from Czech Republic, but there have been no reports of propagation in tick cells. Here we report isolation in a tick cell line of three strains of Ca. R. vini from I. arboricola collected from nests of great tits (Pants major) in Belgium. Internal organs of one male and two engorged female ticks were dissected aseptically, added to cultures of the Rhipicephalus microplus cell line BME/CTVM23 and incubated at 28 degrees C. Rickettsia-like bacteria were first seen in Giemsa-stained cytocentrifuge smears between 2 and 15 weeks later. Two of the isolates grew rapidly, destroying the tick cells within 2-4 weeks of onward passage in BME/CTVM23 cells, while the third isolate grew much more slowly, only requiring subculture at 4 - 5-month intervals. PCR amplification of bacterial 16S rRNA and Rickettsia gltA, sca4, ompB, ompA and 17-kDa genes revealed that all three isolates were Ca. R. vini, with 100 % identity to each other and to published Ca. R. vini sequences from other geographical locations. Transmission electron microscopy revealed typical single Rickettsia bacteria in the cytoplasm of BME/CTVM23 cells. The Ca. R. vini strain isolated from the male I. arboricola tick, designated Boshoek1, was tested for ability to grow in a panel of Ixodes ricinus, Ixodes scapularis and R. microplus cell lines and in Vero cells. The Boshoek1 strain grew rapidly, causing severe cytopathic effect, in the R. microplus line BME26, the I. ricinus line IRE11 and Vero cells, more slowly in the I. ricinus line IRE/CTVM19, possibly established a low-level infection in the I. ricinus line IRE/CTVM20, and failed to infect cells of any of four I. scapularis lines over a 12-week observation period. This study confirmed the applicability of the simple tick organ-cell line co-cultivation technique for isolation of tick-borne Rickettsia spp. using BME/CTVM23 cells. We would like to thank the Tick Cell Biobank at the University of Liverpool and Timothy Kurtti and Ulrike Munderloh of the University of Minnesota for tick cell lines, and Alison Beckett, Aleksandra Beliavskaia and Catherine Hartley of the University of Liverpool for, respectively, assistance with transmission electron microscopy, photomicrographs and provision of uninfected Vero cells. LBS, AA-K and LL were funded by the UK Biotechnology and Biological Sciences Research Council grants BB/P024270/1 and BB/N023889/2; GF is funded by the Fund for Scientific Research (FWO) (Fonds voor Wetenschappelijk Onderzoek-Flanders, Belgium. Grant number G.0538.17) awarded to EM and DH; DH is funded by the Marie Sklodowska-Curie Actions (EUHorizon 2020, Individual Global Fellowship, project no 799609). The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. Bell-Sakyi, L (corresponding author), Univ Liverpool, Inst Infect Vet & Ecol Sci, Dept Infect Biol & Microbiomes, Liverpool Sci Pk IC2,146 Brownlow Hill, Liverpool L3 5RF, Merseyside, England. supervisore2@yahoo.com; L.Bell-Sakyi@liverpool.ac.uk; gerardo.fracasso@uantwerpen.be; lisaluu@liverpool.ac.uk; dieter.heylen@uantwerpen.be; erik.matthysen@uantwerpen.be; jaoteo@riojasalud.es; ampalomar@riojasalud.es

Montane forests worldwide are known centers of endemism and biodiversity but are highly threatened by fragmentation processes. Using data collected in 15 Polylepis forest remnants covering 2000 hectares, we investigated how bird species richness and bird community composition, particularly for species of conservation concern, are influenced by habitat quality and topography in the Tunari National Park in the High Andes of Bolivia. Bird species richness was highest in topographically complex, low-elevation Polylepis patches located in areas with a high potential to retain rainwater. Bird communities differed strongly between Polylepis lanata and P. subtusalbida remnants, each supporting different threatened and endemic species. Within the P. subtusalbida forest, high-elevation fragments characterized by high amounts of sunlight and low anthropogenic disturbance were more likely to contain threatened species. Surprisingly, we found no effect of fragment size on the diversity or composition of bird communities or the presence of bird species of conservation concern. The presence of exotic plantations ( Pinus and/or Eucalyptus spp.) in or outside forest remnants was negatively associated with the number of bird species as well as with occurrence of the endangered Cochabamba-mountain finch ( Compsospiza garleppi ). To support the different communities found in Polylepis forests, these results suggest that conservation efforts should be directed towards both forest types ( P. subtusalbida and P. lanata ) present in the area. For an efficient management of avian diversity, exotic plantations should be established away from native remnants while existing patches should be managed to maintain or increase habitat quality. Finally, the importance of local topography in determining avian species richness and community composition in forest fragments, mainly through topographic controls on moisture distribution and the amount of sunlight received by the fragments, should be considered when planning conservation and reforestation schemes.

The integration and synthesis of the data in different areas of science is drastically slowed and hindered by a lack of standards and networking programmes. Long-term studies of individually marked animals are not an exception. These studies are especially important as instrumental for understanding evolutionary and eco-logical processes in the wild. Furthermore, their number and global distribution provides a unique opportunity to assess the generality of patterns and to address broad-scale global issues (e.g. climate change)., To solve data integration issues and enable a new scale of ecological and evolution-ary research based on long-term studies of birds, we have created the SPI-Birds Network and Database (www.spibirds.org)—a large-scale initiative that connects data from, and researchers working on, studies of wild populations of individually recognizable (usually ringed) birds. Within year and a half since the establishment, SPI-Birds has recruited over 120 members, and currently hosts data on almost 1.5 million individual birds collected in 80 populations over 2,000 cumulative years, and counting., SPI-Birds acts as a data hub and a catalogue of studied populations. It prevents data loss, secures easy data finding, use and integration and thus facilitates collab-oration and synthesis. We provide community-derived data and meta-data stand-ards and improve data integrity guided by the principles of Findable, Accessible, Interoperable and Reusable (FAIR), and aligned with the existing metadata lan-guages (e.g. ecological meta-data language)., The encouraging community involvement stems from SPI-Bird's decentralized ap-proach: research groups retain full control over data use and their way of data management, while SPI-Birds creates tailored pipelines to convert each unique data format into a standard format. We outline the lessons learned, so that other communities (e.g. those working on other taxa) can adapt our successful model. Creating community-specific hubs (such as ours, COMADRE for animal demogra-phy, etc.) will aid much-needed large-scale ecological data integration., The SPI-Birds have been supported by an NWO personal grant (grant number 016.Veni.181.054) to A.C., and a Research Council of Norway grant: 223257 (SFF-III) and 267511 (EVOCLIM).

While numerous studies have reported negative effects of urbanisation on birds, few have examined the role of urban scale in influencing breeding success. Furthermore, many studies have relied on qualitative rather than quantitative assessments of urbanisation. This study sought to address these issues by testing the effects of urbanisation, measured at two spatial scales, on the breeding success of great tits Parus major. A nested study design, incorporating over 400 nestboxes, was used in study sites across northern Belgium with a priori quantified degrees of urbanisation at both local and regional scales. All measured breeding parameters were found to vary at one or both spatial scales of urbanisation; in more urbanised areas great tits displayed advanced laying dates but lower breeding success compared to rural areas, with smaller clutch sizes, lower nestling masses and fewer fledglings per egg. Importantly, urbanisation effects were not limited to big cities as birds breeding in gardens or parks in small towns also had comparatively low success. We found that both regional- and local-scale urbanisation had consistent significant effects on laying date, clutch size and nestling mass, while the number of fledglings per egg was negatively influenced by local-scale urbanisation only. Results of this study therefore highlight the importance of utilising multiple spatial scales in analysing urbanisation effects, as well as the potential negative impact of local urbanisation on breeding success. This calls for further investigation into mechanisms driving urbanisation effects and how these may vary at different scales.

International audience; Understanding species coexistence has long been a major goal of ecology. Coexistence theory for two competing species posits that intraspecific density dependence should be stronger than interspecific density dependence. Great tits and blue tits are two bird species that compete for food resources and nesting cavities. On the basis of long-term monitoring of these two competing species at sites across Europe, combining observational and manipulative approaches, we show that the strength of density regulation is similar for both species, and that individuals have contrasting abilities to compete depending on their age. For great tits, density regulation is driven mainly by intraspecific competition. In contrast, for blue tits, interspecific competition contributes as much as intraspecific competition, consistent with asymmetric competition between the two species. In addition, including age-specific effects of intra-and interspecific competition in density-dependence models improves predictions of fluctuations in population size by up to three times.

Green spaces in the city are important for human wellbeing, but are also zones in which humans can become infected with zoonotic diseases. Therefore, there is a need to understand how infection risk is related to green space characteristics, wildlife communities and connectivity with rural areas hosting reservoir populations of hosts. Our hypothesis is that wildlife hosts in urban green spaces, and thereby the prevalence of questing ticks and their Lyme disease causing pathogens (Borrelia burgdorferi s.l.), can be partly predicted based on green space characteristics as well as measures of connectivity to known source areas. We sampled ticks in twenty-two green spaces during Spring (2014 and 2016) and Autumn 2016, located along an urbanization gradient in Antwerp (Belgium). More than 18,000 m2 was sampled, with tick densities ranging from 0 to 386 individuals/100 m2. We estimated connectivity using the least-cost algorithm as either the cost distance to the nearest green space, or to a known population of roe deer (Capreolus capreolus), known to be an important tick propagation host. Both connectivity measures turned out to be correlated, reflecting a gradient in green space isolation from the periphery to the urban center. In 87% of plots where ticks were trapped, at least one Borrelia-infected tick was found. The overall Borrelia-prevalence in nymphs was 17.8%, in adults 32.6%. Density of infected ticks decreased with urbanization and increased with connectivity. Nymphs in larger green spaces were more likely to be infected. While density and infection prevalence for adults increased with the amount of neighboring agricultural land, the larval density and nymphal infection prevalence decreased. Interestingly, the proportion of Borrelia genospecies associated with birds or mammals was comparable in rural and (sub)urban areas (bird/mammal: 0.38), suggesting that even in small green spaces Borrelia infections can persist in local host populations.

A major aim of evolutionary biology is to understand why patterns of genomic variation vary among populations and species. Large-scale genomic studies of widespread species are useful for studying how the environment and demographic history shape patterns of genomic divergence, and with the continually decreasing cost of sequencing, such studies are now becoming feasible. Here, we carry out one of the most comprehensive surveys of genomic variation in a wild vertebrate to date; the great tit ( Parus major ) HapMap project. We screened ca 500,000 SNP markers across 647 individuals from 29 populations, spanning almost the entire geographic range of the European great tit subspecies. We found that genome-wide variation was consistent with a recent colonisation across Europe from a single refugium in the Balkans and/or Turkey, with bottlenecks and reduced genetic diversity in island populations. Differentiation across the genome was highly heterogeneous, with clear “islands of differentiation” even among populations which are ostensibly panmictic. These islands of differentiation were consistently found in regions of low recombination, suggesting that background selection can rapidly promote population differentiation among even the most recently colonised populations. We also detected genomic outlier regions that were unique to peripheral great tit populations, most likely as a result of recent directional selection at the range edges of this species. These “unique” outlier regions contained candidate genes for morphology, thermal adaptation and colouration, supporting previous research in this species, and providing avenues for future investigation. Our study suggests that comprehensive screens of genomic variation in wild organisms can provide unique insights into evolution. Author summary Studying patterns of genetic variation is a useful way of determining why populations and species differ in nature. Genetic variation is shaped by natural selection, but also by the present and past size of populations, the amount of migration, and by features of the genome, such as variation in recombination rate, of the organism being studied. Teasing apart the effects of these different processes on genomic diversity is difficult, but one way that this can be achieved is by studying genomic variation across the entire range of a species. We performed a continental-scale analysis of genetic variation in the great tit - a widespread songbird that has been the focus of extensive ecological research. We first used genomic data to reconstruct the historical colonisation of great tits across Europe, and showed that during the last ice age, this species was likely restricted to a single region in Eastern Europe, from which they spread across the continent. We then studied how patterns of variation differ along the genome, and show that recombination rate is a key driver of variation among all populations. Importantly, by comparing many populations we were able to identify genes that have been subject to natural selection in specific geographical regions. We found that natural selection appeared to be strongest in populations on the edges of the great tit’s range acting on traits such as morphology, stress response and colouration. Large-scale genetic analyses such as ours are therefore useful approaches for understanding how evolution operates in the wild.

The risk of tick-borne disease in humans depends on the exposure to pathogen-infected ticks, which in turn is driven by local tick population densities, pathogen prevalence and human activity. Variation in tick densities and pathogen prevalence between green spaces differing in habitat characteristics, location and geography has been well documented. In contrast, variation within green spaces, although vital for management and prevention of disease risk, remains poorly understood. Studying this variation may lead to a better understanding of the drivers of small-scale tick distribution and reveal priority locations for tick management. We sampled ticks within green spaces at three location types representing different green space infrastructures and levels of human activity: (1) a structural element (e.g. bench); (2) the ecotone 40 m further along the adjacent trail and; (3) the interior of the associated forest stand, 20 m perpendicular to the trail, between (1) and (2). Drag sampling took place in 2018 and 2019 at 36 locations in 10 green spaces located in the Campine region of Flanders, Belgium. The density of questing nymphs (DON) was lowest at structural elements and slightly higher adjacent to trails. The highest tick densities were recorded in the forest interior. DON was higher in deciduous than in coniferous forests as well as in stands with a more developed shrub layer. This was true for all location types, as we observed a strong correlation of DON between location types within forest stands. This enables the prediction of DON within forest stands, thus enabling the prediction of DON near infrastructure based on the associated forest stand characteristics. Prevention and management efforts should be focused on infrastructure in or adjacent to deciduous, structure-rich forest stands, although large variation in DON at all location types indicates overall, factual risk while using green space infrastructure. This work was supported by the Research Foundation - Flanders [grant number 60897] Van Gestel, M (corresponding author), Campus Drie Eiken,Room D1-46,Univ Pl 1, B-2610 Antwerp, Belgium. Mats.vangestel@uantwerpen.be

Gene flow is usually thought to reduce genetic divergence and impede local adaptation by homogenising gene pools between populations. However, evidence for local adaptation and phenotypic differentiation in highly mobile species, experiencing high levels of gene flow, is emerging. Assessing population genetic structure at different spatial scales is thus a crucial step towards understanding mechanisms underlying intraspecific differentiation and diversification. Here, we studied the population genetic structure of a highly mobile species - the great tit Parus major - at different spatial scales. We analysed 884 individuals from 30 sites across Europe including 10 close-by sites (< 50 km), using 22 microsatellite markers. Overall we found a low but significant genetic differentiation among sites (F-ST = 0.008). Genetic differentiation was higher, and genetic diversity lower, in south-western Europe. These regional differences were statistically best explained by winter temperature. Overall, our results suggest that great tits form a single patchy metapopulation across Europe, in which genetic differentiation is independent of geographical distance and gene flow may be regulated by environmental factors via movements related to winter severity. This might have important implications for the evolutionary trajectories of sub-populations, especially in the context of climate change, and calls for future investigations of local differences in costs and benefits of philopatry at large scales. (C) 2016 The Linnean Society of London, The study was funded by the Swiss National Science Foundation (3100A0-102017 to HR, P2BEP3_152103 to KL and PMPDP3_151361/161858 to ML). We thank L. Gustafsson and J. Forsman who kindly allowed us to use their nest boxes. We gratefully thank E. Bezault, L. Cornetti and two anonymous reviewers for valuable advice on genetic analyses and helpful comments on the manuscript. All samples were collected under licenses of national authorities and financially supported by the Academy of Finland grant (to NP and 265859 to TE), the Netherland Organisation for Scientific Research (NWO-VICI 86503003 to JK and NWO-VICI to MV), the Netherlands Genomics Initiative (Horizon grant to KvO), the Hungarian Scientific Research Fund (OTKA 75618 to JT), the Estonian Ministry of Education and Science (IUT 34-8 to RM), the OSU-OREME, the Spanish Ministry of Education and Science (CGL2010-21933-CO-02 to EB), the Portuguese Foundation for Science and Technology (SFRH/BD/13594/2003 to ACN) and the Agence Nationale de la Recherche (ANR-08-JCJC-0041-01 to BD).

SUMMARYLyme disease is caused by bacteria of theBorrelia burgdorferigenospecies complex and transmitted by Ixodid ticks. In North America only one pathogenic genospecies occurs, in Europe there are several. According to the dilution effect hypothesis (DEH), formulated in North America, nymphal infection prevalence (NIP) decreases with increasing host diversity since host species differ in transmission potential. We analysedBorreliainfection in nymphs from 94 forest stands in Belgium, which are part of a diversification gradient with a supposedly related increasing host diversity: from pine stands without to oak stands with a shrub layer. We expected changing tree species and forest structure to increase host diversity and decrease NIP. In contrast with the DEH, NIP did not differ between different forest types. Genospecies diversity however, and presumably also host diversity, was higher in oak than in pine stands. Infected nymphs tended to harbourBorrelia afzeliiinfection more often in pine stands whileBorrelia gariniiandBorrelia burgdorferiss. infection appeared to be more prevalent in oak stands. This has important health consequences, since the latter two cause more severe disease manifestations. We show that the DEH must be nuanced for Europe and should consider the response of multiple pathogenic genospecies.

The red squirrel (Sciurus vulgaris) population in the United Kingdom has declined over the last century and is now on the UK endangered species list. This is the result of competition from the eastern grey squirrel (S. carolinensis) which was introduced in the 19th century. However, recent evidence suggests that the rate of population decline is enhanced by squirrelpox disease, caused by a viral infection carried asymptomatically by grey squirrels but to which red squirrels are highly susceptible. Population genetic diversity provides some resilience to rapidly evolving or exotic pathogens. There is currently no data on genetic diversity of extant UK squirrel populations with respect to genes involved in disease resistance. Diversity is highest at loci involved in the immune response including genes clustered within the major histocompatibility complex (MHC). Using the class II DRB locus as a marker for diversity across the MHC region we genotyped 110 red squirrels from locations in the UK and continental Europe. Twenty-four Scvu-DRB alleles at two functional loci; Scvu-DRB1 and Scvu-DRB2, were identified. High levels of diversity were identified at both loci in the continental populations. In contrast, no diversity was observed at the Scvu-DRB2 locus in the mainland UK population while a high level of homozygosity was observed at the Scvu-DRB1 locus. The red squirrel population in the UK appears to lack the extensive MHC diversity associated with continental populations, a feature which may have contributed to their rapid decline.

Dispersal and migration are superficially similar large-scale movements, but which appear to differ in terms of inter-individual behavioural synchronization. Seasonal migration is a striking example of coordinated behaviour, enabling animal populations to track spatio-temporal variation in ecological conditions. By contrast, for dispersal, while social context may influence an individual's emigration and settlement decisions, transience is believed to be mostly a solitary behaviour. Here, we review differences in drivers that may explain why migration appears to be more synchronized than dispersal. We derive the prediction that the contrast in the importance of behavioural synchronization between dispersal and migration is linked to differences in the selection pressures that drive their respective evolution. Although documented examples of collective dispersal are rare, this behaviour may be more common than currently believed, with important consequences for eco-evolutionary dynamics. Crucially, to date, there is little available theory for predicting when we should expect collective dispersal to evolve, and we also lack empirical data to test predictions across species. By reviewing the state of the art in research on migration and collective movements, we identify how we can harness these advances, both in terms of theory and data collection, to broaden our understanding of synchronized dispersal and its importance in the context of global change.

Many vector-borne diseases are transmitted through complex pathogen-vector-host networks, which makes it challenging to identify the role of specific host groups in disease emergence. Lyme borreliosis in humans is now the most common vector-borne zoonosis in the Northern Hemisphere. The disease is caused by multiple genospecies of Borrelia burgdorferi sensu lato bacteria transmitted by ixodid (hard) ticks, and the major host groups transmit Borrelia genospecies with different pathogenicity, causing variable clinical symptoms in humans. The health impact of a given host group is a function of the number of ticks it infects as well as the pathogenicity of the genospecies it carries. Borrelia afzelii, with mainly small mammals as reservoirs, is the most common pathogen causing Lyme borreliosis, and it is often responsible for the largest proportion of infected host-seeking tick nymphs in Europe. The bird-borne Borrelia garinii, though less prevalent in nymphal ticks, is more likely to cause Lyme neuroborreliosis, but whether B. garinii causes disseminated disease more frequently has not been documented. Based on extensive data of annual disease incidence across Norway from 1995 to 2017, we show here that 69% of disseminated Lyme borreliosis cases were neuroborreliosis, which is three times higher than predicted from the infection prevalence of B. garinii in host-seeking ticks (21%). The population estimate of migratory birds, mainly of thrushes, explained part of the annual variation in cases of neuroborreliosis, with a one-year time lag. We highlight the important role of the genospecies' pathogenicity and the host associations for understanding the epidemiology of disseminated Lyme borreliosis. We are grateful to the Research Council of Norway and the Norwegian Environment Agency funding the #EcoTick project (254469). A.M. is grateful for the travel grant from the Faculty of Mathematics and Natural Sciences, UiO as part of a sabbatical in Antwerp, Belgium, to work on this project. D.J.A.H. is funded by the Marie Sklodowska-Curie Actions (EU-Horizon 2020, Individual Global Fellowship, project no. 799609), the Fund for Scientific Research-Flanders (FWO) and the Bill & Melinda Gates Foundation.