Parasite load and seasonal migration in red deer

Elucidating nematode diversity and prevalence in moose across a wide latitudinal gradient using DNA metabarcoding

Parasitic nematodes are ubiquitous and can negatively impact their host by reducing fecundity or increasing mortality, yet the driver of variation in the parasite community across a wildlife host's geographic distribution remains elusive for most species. Based on an extensive collection of fecal samples (n = 264) from GPS marked moose (Alces alces), we used DNA metabarcoding to characterize the individual (sex, age class) and seasonal parasitic nematode community in relation to habitat use and migration behavior in five populations distributed across a wide latitudinal gradient (59.6°N to 70.5°N) in Norway. We detected 21 distinct nematode taxa with the six most common being Ostertagia spp., Nematodirella spp., Trichostongylus spp., T. axei, Elaphostrongylus alces, and an unclassified Strongylida. There was higher prevalence of livestock parasites in areas with larger sheep populations indicating a higher risk of spillover events. The individual level nematode richness was mostly consistent across study areas, while the number and type of nematode taxa detected at each study area varied considerably but did not follow a latitudinal gradient. While migration distance affected nematode beta-diversity across all sites, it had a positive effect on richness at only two of the five study areas suggesting population specific effects. Unexpectedly, nematode richness was higher in winter than summer when very few nematodes were detected. Here we provide the first extensive description of the parasitic nematode community of moose across a wide latitudinal range. Overall, the population-specific impact of migration on parasitism across the distribution range and variation in sympatry with other ruminants suggest local characteristics affect host-parasite relationships.

A New Endemic Locality of Dermacentor reticulatus in Central-Southern Poland and Its Potential Epidemiological Implications

Dermacentor reticulatus (Acari: Ixodidae) is an important arthropod vector in medical and veterinary contexts. Its geographic range is divided into western and eastern populations separated by a "Dermacentor-free zone" in central Poland. Recent faunistic studies showed a new endemic locality of the species in Upper Silesia to the west of the Vistula River (central-southern Poland) and its co-occurrence with I. ricinus. The prevalence of five tick-borne pathogens (TBPs), e.g., B. burgdorferi s.l., Bartonella spp., Rickettsia spp., and Babesia spp., in the ticks was assessed with polymerase chain reaction (PCR) methods. The molecular studies revealed the presence of Rickettsia spp. in 23.8% of the D. reticulatus specimens. In turn, 94.1% of the I. ricinus adults were infected with B. burgdorferi s.l., 11.7 % with Babesia spp., and 5.8% with Rickettsia spp. Coinfections with two TBPs were noted in 17.6% of the I. ricinus. These findings highlight not only the risk of infestation by both tick species in an area previously considered Dermacentor-free, but also the high prevalence of TBPs in the study area. Increased focus on medical and veterinary services appears necessary to diagnose and prevent tick-borne diseases in this region.

Experience reduces route selection for conspecifics by the collectively migrating white stork

Migration can be an energetically costly behavior with strong fitness consequences in terms of mortality and reproduction.1,2,3,4,5,6,7,8,9,10,11 Migrants should select migratory routes to minimize their costs, but both costs and benefits may change with experience.12,13,14 This raises the question of whether experience changes how individuals select their migratory routes. Here, we investigate the effect of age on route selection criteria in a collectively migrating soaring bird, the white stork (Ciconia ciconia). We perform step-selection analysis on a longitudinal dataset tracking 158 white storks over up to 9 years to quantify how they select their routes based on the social and atmospheric environments and to examine how this selection changes with age. We find clear ontogenetic shifts in route selection criteria. Juveniles choose routes that have good atmospheric conditions and high conspecific densities. Yet, as they gain experience, storks' selection on the availability of social information reduces-after their fifth migration, experienced birds also choose routes with low conspecific densities. Thus, our results suggest that as individuals age, they gradually replace information gleaned from other individuals with information gained from experience, allowing them to shift their migration timing and increasing the timescale at which they select their routes.

A unified evolutionary framework for understanding parasite infection and host migratory behaviour

Animal migration impacts organismal health and parasite transmission: migrants are simultaneously exposed to parasites and able to reduce infection for both individuals and populations. However, these dynamics are difficult to study; empirical studies reveal disparate results while existing theory makes assumptions that simplify natural complexity. Here, we systematically review empirical studies of migration and infection across taxa, highlighting key gaps in our understanding. Next, we develop a unified evolutionary framework incorporating different selective pressures of parasite-migration interactions while accounting for ecological complexity that goes beyond previous theory. Our framework generates diverse migration-infection patterns paralleling those seen in empirical systems, including partial and differential migration. Finally, we generate predictions about which mechanisms dominate which empirical systems to guide future studies. Our framework provides an overarching understanding of selective pressures shaping migration patterns in the context of animal health and disease, which is critical for predicting how environmental change may threaten migration.

Laser ablation strontium isotopes and spatial assignment show seasonal mobility in red deer (Cervus elaphus) at Lazaret Cave, France (MIS 6)

Zooarchaeological analysis is a useful means of exploring faunal palaeoecology, paleoclimate and past human behaviours. The Middle Pleistocene archaeological site Lazaret Cave, located in modern-day Nice, France, features a vast assemblage of faunal remains pertinent to the understanding of early Neanderthal subsistence behaviours as well as red deer (Cervus elaphus) ecology during MIS 6. This pilot study examines materials from archaeological layer UA25, a short-term occupation layer at Lazaret dating to ~150,000 years ka, which has revealed 28 early Neanderthal remains as well as thousands of faunal bones, of which red deer and ibex (Capra ibex) are most abundant. Molars from three red deer mandibles and a single ibex were analysed for strontium (87Sr/86Sr) isotopic analysis using laser ablation mass spectrometry to determine animal movements during tooth formation, combined with intra-tooth oxygen (δ18O) isotope analysis to determine seasonality. The isotope data was modelled within a local 87Sr/86Sr isoscape and computational spatial assignment was undertaken to reconstruct potential summer and winter ranges of red deer. Results from this pilot study show seasonal mobility within 20 km of Lazaret, identifying two possible summer and winter ranges for the red deer excavated from UA25. Both possible summer ranges are located at higher elevations further from Lazaret while winter ranges have been assigned to lower elevations closer to the coastline and closer to Lazaret. The ibex shows no 87Sr/86Sr variation throughout the first, second and third molar and the spatial assignment indicates it lived proximal to the site during the period of tooth formation. In addition to providing the first evidence of red deer spatial ecology in southern France during MIS 6, we also infer from the faunal isotope data that hominins at Lazaret Cave were likely hunting red deer in autumn and winter when they were closer to the cave site, while hunting in summer would have required up to 20 km of travel.

The emergence and shift in seasonality of Lyme borreliosis in Northern Europe

Climate change has had a major impact on seasonal weather patterns, resulting in marked phenological changes in a wide range of taxa. However, empirical studies of how changes in seasonality impact the emergence and seasonal dynamics of vector-borne diseases have been limited. Lyme borreliosis, a bacterial infection spread by hard-bodied ticks, is the most common vector-borne disease in the northern hemisphere and has been rapidly increasing in both incidence and geographical distribution in many regions of Europe and North America. By analysis of long-term surveillance data (1995-2019) from across Norway (latitude 57°58'-71°08' N), we demonstrate a marked change in the within-year timing of Lyme borreliosis cases accompanying an increase in the annual number of cases. The seasonal peak in cases is now six weeks earlier than 25 years ago, exceeding seasonal shifts in plant phenology and previous model predictions. The seasonal shift occurred predominantly in the first 10 years of the study period. The concurrent upsurgence in case number and shift in case timing indicate a major change in the Lyme borreliosis disease system over recent decades. This study highlights the potential for climate change to shape the seasonal dynamics of vector-borne disease systems.

Effect of sex on the gut microbiota characteristics of passerine migratory birds

The gut microbiota, considered the “invisible organ” in the host animal, has been extensively studied recently. However, knowledge about the gut microbiota characteristics of passerine migratory birds during migration is limited. This study investigated the gut microbiota characteristics of three dominant migratory bird species (namely orange-flanked bluetail Tarsiger cyanurus, yellow-throated bunting Emberiza elegans, and black-faced bunting Emberiza spodocephala) in the same niche during spring migration and whether they were bird sex-specific. The compositions of gut microbiota species in these three migratory bird species and their male and female individuals were found to be similar. The main bacterial phyla were Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes, and the main genera were Lactobacillus, Acinetobacter, Rickettsiella, and Mycobacterium; however, their relative abundance was different. Moreover, some potential pathogens and beneficial bacteria were found in all the three bird species. Alpha diversity analysis showed that in T. cyanurus, the richness and diversity of the gut microbiota were higher in male individuals than in female individuals, while the opposite was true for E. elegans and E. spodocephala. The alpha diversity analysis showed significant differences between male and female individuals of E. elegans (p < 0.05). The beta diversity analysis also revealed that the gut microbial community structure differed significantly between the male and female individuals of the three migratory bird species.

The effects of population management on wild ungulates: A systematic map of evidence for UK species

INTRODUCTION

Over recent decades, the abundance and geographic ranges of wild ungulate species have expanded in many parts of Europe, including the UK. Populations are managed to mitigate their ecological impacts using interventions, such as shooting, fencing and administering contraception. Predicting how target species will respond to interventions is critical for developing sustainable, effective and efficient management strategies. However, the quantity and quality of evidence of the effects of interventions on ungulate species is unclear. To address this, we systematically mapped research on the effects of population management on wild ungulate species resident in the UK.

METHODS

We searched four bibliographic databases, Google Scholar and nine organisational websites using search terms tested with a library of 30 relevant articles. Worldwide published peer-reviewed articles were considered, supplemented by 'grey' literature from UK-based sources. Three reviewers identified and screened articles for eligibility at title, abstract and full-text levels, based on predefined criteria. Data and metadata were extracted and summarised in a narrative synthesis supported by structured graphical matrices.

RESULTS

A total of 123 articles were included in the systematic map. Lethal interventions were better represented (85%, n = 105) than non-lethal interventions (25%, n = 25). Outcomes related to demography and behaviour were reported in 95% of articles (n = 117), whereas effects on health, physiology and morphology were studied in only 11% of articles (n = 14). Well-studied species included wild pigs (n = 58), red deer (n = 28) and roe deer (n = 23).

CONCLUSIONS

Evidence for the effects of population management on wild ungulate species is growing but currently limited and unevenly distributed across intervention types, outcomes and species. Priorities for primary research include: species responses to non-lethal interventions, the side-effects of shooting and studies on sika deer and Chinese muntjac. Shooting is the only intervention for which sufficient evidence exists for systematic review or meta-analysis.

Clair C, Kutz SJ, Hebblewhite M, Merrill EH. What makes elk tick: winter tick (Dermacentor albipictus) grooming behavior in wild elk (Cervus canadensis)

Ungulates groom to remove ectoparasites but grooming may interfere with foraging, vigilance, and rumination, and it is possible that these effects differ among migratory tactics due to differences in parasite infestations. We compared the effects of grooming for winter ticks (Dermacentor albipictus) on winter foraging behavior by migrating and resident elk (Cervus canadensis) in the partially migratory population at the Ya Ha Tinda, adjacent to Banff National Park, Canada. We used hair loss on the dorsal shoulder area (“withers”) measured from photographic images as an index of tick infestation of individual elk. We conducted 594 focal observations on 48 radio-collared and 18 uncollared individuals that were uniquely identifiable from ear-tags (N = 66) in 2019 to assess whether grooming for ticks in winter reduced time spent foraging, ruminating, or being vigilant. Because rubbing or hair loss from radio-collars may influence tick infestations and behavior, we controlled for whether elk were collared or uncollared in our analyses. Neck hair loss was 3−5% greater in collared elk than uncollared elk, but neither withers hair loss nor time spent grooming differed. Grooming occurred during 42% of the observations but grooming comprised only ~1% of observation time. Nevertheless, 40% of all grooming was observed during resting, and grooming interrupted vigilance behavior ~8 times more than foraging. We found no differences among elk following different migratory tactics in time spent grooming or in other behaviors, but one of the two groups of migrant elk had higher withers hair loss. Our results suggest winter ticks may have slight effects on elk relative to other ungulates, particularly moose (Alces alces), in North America.

Variation in movement patterns of mule deer: have we oversimplified migration?

BACKGROUND

Conservation and management of migratory animals has gained attention in recent years, but the majority of research has focused on stereotypical 'migrant' and 'resident' behaviors, often failing to incorporate any atypical behaviors or characterize migratory behaviors beyond distance and timing of the migration. With migration threatened by anthropogenic development and climate change, it is crucial that we understand the full range of migratory behaviors. Our objective was to demonstrate and characterize the variation in migration strategies, including typical and atypical migratory behaviors for mule deer (Odocoileus hemionus) in Utah, USA.

METHODS

Because calculation of common metrics such as distance, timing, and use of stopovers during migration did not adequately describe the variation we observed in migratory behavior for this species-particularly when animals visited multiple (> 3) ranges for extended lengths of time-we developed additional methods and categories to describe observed variation in migratory behavior. We first categorized trajectories based on the number of discrete, separate ranges and range shifts between them. Then, we further characterized the variation in migration strategies by examining the timing, duration, and distance traveled within each of the categories. We also examined if and how frequently individual deer switched among categories from year to year.

RESULTS

We classified 1218 movement trajectories from 722 adult female mule deer, and found that 54.4% were dual-range migrants, who made one round-trip to one distinct range. Multi-range migrants (23.6%) made one round-trip during which they stayed at multiple discrete ranges. Commuters (1.0%) traveled to the same range multiple times, and poly migrants (1.5%) made multiple round-trips to different ranges. Gradual movers (2.5%) did not show a discrete range shift but moved gradually between ranges, whereas residents (12.6%) never left their home ranges, and dispersers (4.4%) left but never returned. Of the deer that we monitored for multiple years, 51.2% switched among categories.

CONCLUSION

We conclude that the substantial number of atypical migratory strategies, as well as the number of deer that switched categories, underlines the importance of studying these less-stereotyped behaviors that may be exhibited by large proportions of populations. Acknowledging and investigating the full complexity and diversity in migratory strategies might uncover unknowns with respect to underlying factors and drivers of migration, and can help shape effective conservation strategies.

The Contribution of Wildlife Hosts to the Rise of Ticks and Tick-Borne Diseases in North America

Wildlife vertebrate hosts are integral to enzootic cycles of tick-borne pathogens, and in some cases have played key roles in the recent rise of ticks and tick-borne diseases in North America. In this forum article, we highlight roles that wildlife hosts play in the maintenance and transmission of zoonotic, companion animal, livestock, and wildlife tick-borne pathogens. We begin by illustrating how wildlife contribute directly and indirectly to the increase and geographic expansion of ticks and their associated pathogens. Wildlife provide blood meals for tick growth and reproduction; serve as pathogen reservoirs; and can disperse ticks and pathogens-either through natural movement (e.g., avian migration) or through human-facilitated movement (e.g., wildlife translocations and trade). We then discuss opportunities to manage tick-borne disease through actions directed at wildlife hosts. To conclude, we highlight key gaps in our understanding of the ecology of tick-host interactions, emphasizing that wildlife host communities are themselves a very dynamic component of tick-pathogen-host systems and therefore complicate management of tick-borne diseases, and should be taken into account when considering host-targeted approaches. Effective management of wildlife to reduce tick-borne disease risk further requires consideration of the 'human dimensions' of wildlife management. This includes understanding the public's diverse views and values about wildlife and wildlife impacts-including the perceived role of wildlife in fostering tick-borne diseases. Public health agencies should capitalize on the expertise of wildlife agencies when developing strategies to reduce tick-borne disease risks.

Spatial and temporal dynamics of space use by free-ranging domestic dogs Canis familiaris in rural Africa

Variation in the spatial ecology of animals influences the transmission of infections and so understanding host behavior can improve the control of diseases. Despite the global distribution of free-ranging domestic dogs Canis familiaris and their role as reservoirs for zoonotic diseases, little is known about the dynamics of their space use. We deployed GPS loggers on owned but free-ranging dogs from six villages in rural Chad, and tracked the movements of 174 individuals in the dry season and 151 in the wet season. We calculated 95% and core home ranges using auto-correlated kernel density estimates (AKDE₉₅ and AKDE_core ), determined the degree to which their movements were predictable, and identified correlates of movement patterns. The median AKDE₉₅ range in the dry season was 0.54 km² and in the wet season was 0.31 km² , while the median AKDE_core range in the dry season was 0.08 km² and in the wet season was 0.04 km² . Seasonal variation was, in part, related to owner activities; dogs from hunting households had ranges that were five times larger in the dry season. At least 70% of individuals were more predictably "at home" (<50 m from the household) throughout the day in the dry season, 80% of dogs demonstrated periodicity in activity levels (speed), and just over half the dogs exhibited periodicity in location (repeated space use). In the wet season, dogs mostly exhibited 24-h cycles in activity and location, with peaks at midday. In the dry season, dogs exhibited both 12- and 24-h cycles, with either a single peak at midday, or one peak between 06:00 and 12:00 and a second between 18:00 and 22:00. Strategies to control canine-mediated zoonoses can be improved by tailoring operations to the local spatial ecology of free-ranging dogs. Interventions using a door-to-door strategy in rural Chad would best conduct operations during the dry season, when access to dogs around their household more reliably exceeds 70% throughout the day. Given the importance of use in hunting for explaining variation in dog space-use, targeting approaches to disease control at the household level on the basis of owner activities offers potential to improve access to dogs.

Leveraging genomics to understand threats to migratory birds

Understanding how risk factors affect populations across their annual cycle is a major challenge for conserving migratory birds. For example, disease outbreaks may happen on the breeding grounds, the wintering grounds, or during migration and are expected to accelerate under climate change. The ability to identify the geographic origins of impacted individuals, especially outside of breeding areas, might make it possible to predict demographic trends and inform conservation decision-making. However, such an effort is made more challenging by the degraded state of carcasses and resulting low quality of DNA available. Here, we describe a rapid and low-cost approach for identifying the origins of birds sampled across their annual cycle that is robust even when DNA quality is poor. We illustrate the approach in the common loon (Gavia immer), an iconic migratory aquatic bird that is under increasing threat on both its breeding and wintering areas. Using 300 samples collected from across the breeding range, we develop a panel of 158 single-nucleotide polymorphisms (SNP) loci with divergent allele frequencies across six genetic subpopulations. We use this SNP panel to identify the breeding grounds for 142 live nonbreeding individuals and carcasses. For example, genetic assignment of loons sampled during botulism outbreaks in parts of the Great Lakes provides evidence for the significant role the lakes play as migratory stopover areas for loons that breed across wide swaths of Canada, and highlights the vulnerability of a large segment of the breeding population to botulism outbreaks that are occurring in the Great Lakes with increasing frequency. Our results illustrate that the use of SNP panels to identify breeding origins of carcasses collected during the nonbreeding season can improve our understanding of the population-specific impacts of mortality from disease and anthropogenic stressors, ultimately allowing more effective management.

Animal migrations and parasitism: reciprocal effects within a unified framework

Migrations, i.e. the recurring, roundtrip movement of animals between distant and distinct habitats, occur among diverse metazoan taxa. Although traditionally linked to avoidance of food shortages, predators or harsh abiotic conditions, there is increasing evidence that parasites may have played a role in the evolution of migration. On the one hand, selective pressures from parasites can favour migratory strategies that allow either avoidance of infections or recovery from them. On the other hand, infected animals incur physiological costs that may limit their migratory abilities, affecting their speed, the timing of their departure or arrival, and/or their condition upon reaching their destination. During migration, reduced immunocompetence as well as exposure to different external conditions and parasite infective stages can influence infection dynamics. Here, we first explore whether parasites represent extra costs for their hosts during migration. We then review how infection dynamics and infection risk are affected by host migration, thereby considering parasites as both causes and consequences of migration. We also evaluate the comparative evidence testing the hypothesis that migratory species harbour a richer parasite fauna than their closest free-living relatives, finding general support for the hypothesis. Then we consider the implications of host migratory behaviour for parasite ecology and evolution, which have received much less attention. Parasites of migratory hosts may achieve much greater spatial dispersal than those of non-migratory hosts, expanding their geographical range, and providing more opportunities for host-switching. Exploiting migratory hosts also exerts pressures on the parasite to adapt its phenology and life-cycle duration, including the timing of major developmental, reproduction and transmission events. Natural selection may even favour parasites that manipulate their host's migratory strategy in ways that can enhance parasite transmission. Finally, we propose a simple integrated framework based on eco-evolutionary feedbacks to consider the reciprocal selection pressures acting on migratory hosts and their parasites. Host migratory strategies and parasite traits evolve in tandem, each acting on the other along two-way causal paths and feedback loops. Their likely adjustments to predicted climate change will be understood best from this coevolutionary perspective.

Elk migration influences the risk of disease spillover in the Greater Yellowstone Ecosystem

Wildlife migrations provide important ecosystem services, but they are declining. Within the Greater Yellowstone Ecosystem (GYE), some elk Cervus canadensis herds are losing migratory tendencies, which may increase spatiotemporal overlap between elk and livestock (domestic bison Bison bison and cattle Bos taurus), potentially exacerbating pathogen transmission risk.

We combined disease, movement, demographic and environmental data from eight elk herds in the GYE to examine the differential risk of brucellosis transmission (through aborted foetuses) from migrant and resident elk to livestock.

For both migrants and residents, we found that transmission risk from elk to livestock occurred almost exclusively on private ranchlands as opposed to state or federal grazing allotments. Weather variability affected the estimated distribution of spillover risk from migrant elk to livestock, with a 7%–12% increase in migrant abortions on private ranchlands during years with heavier snowfall. In contrast, weather variability did not affect spillover risk from resident elk.

Migrant elk were responsible for the majority (68%) of disease spillover risk to livestock because they occurred in greater numbers than resident elk. On a per‐capita basis, however, our analyses suggested that resident elk disproportionately contributed to spillover risk. In five of seven herds, we estimated that the per‐capita spillover risk was greater from residents than from migrants. Averaged across herds, an individual resident elk was 23% more likely than an individual migrant elk to abort on private ranchlands.

Our results demonstrate links between migration behaviour, spillover risk and environmental variability, and highlight the utility of integrating models of pathogen transmission and host movement to generate new insights about the role of migration in disease spillover risk. Furthermore, they add to the accumulating body of evidence across taxa that suggests that migrants and residents should be considered separately during investigations of wildlife disease ecology. Finally, our findings have applied implications for elk and brucellosis in the GYE. They suggest that managers should prioritize actions that maintain spatial separation of elk and livestock on private ranchlands during years when snowpack persists into the risk period.

Red and fallow deer determine the density of Ixodes ricinus nymphs containing Anaplasma phagocytophilum

Background

The density of Ixodes ricinus nymphs infected with Anaplasma phagocytophilum is one of the parameters that determines the risk for humans and domesticated animals to contract anaplasmosis. For this, I. ricinus larvae need to take a bloodmeal from free-ranging ungulates, which are competent hosts for A. phagocytophilum.

Methods

Here, we compared the contribution of four free-ranging ungulate species, red deer (Cervus elaphus), fallow deer (Dama dama), roe deer (Capreolus capreolus), and wild boar (Sus scrofa), to A. phagocytophilum infections in nymphs. We used a combination of camera and live trapping to quantify the relative availability of vertebrate hosts to questing ticks in 19 Dutch forest sites. Additionally, we collected questing I. ricinus nymphs and tested these for the presence of A. phagocytophilum. Furthermore, we explored two potential mechanisms that could explain differences between species: (i) differences in larval burden, which we based on data from published studies, and (ii) differences in associations with other, non-competent hosts.

Results

Principal component analysis indicated that the density of A. phagocytophilum-infected nymphs (DIN) was higher in forest sites with high availability of red and fallow deer, and to a lesser degree roe deer. Initial results suggest that these differences are not a result of differences in larval burden, but rather differences in associations with other species or other ecological factors.

Conclusions

These results indicate that the risk for contracting anaplasmosis in The Netherlands is likely highest in the few areas where red and fallow deer are present. Future studies are needed to explore the mechanisms behind this association.

Graphical abstract

Parasite intensity and the evolution of migratory behavior

Migration can allow individuals to escape parasite infection, which can lead to a lower infection probability (prevalence) in a population and/or fewer parasites per individual (intensity). Because individuals with more parasites often have lower survival and/or fecundity, infection intensity shapes the life-history trade-offs determining when migration is favored as a strategy to escape infection. Yet, most theory relies on susceptible-infected (SI) modeling frameworks, defining individuals as either healthy or infected, ignoring details of infection intensity. Here, we develop a novel modeling approach that captures infection intensity as a spectrum, and ask under what conditions migration evolves as function of how infection intensity changes over time. We show that relative timescales of migration and infection accumulation determine when migration is favored. We also find that population-level heterogeneity in infection intensity can lead to partial migration, where less-infected individuals migrate while more infected individuals remain resident. Our model is one of the first to consider how infection intensity can lead to migration. Our results frame migratory escape in light of infection intensity rather than prevalence, thus demonstrating that decreased infection intensity should be considered a benefit of migration, alongside other typical drivers of migration.

Ticks in the ecotone: the impact of agri-environment field margins on the presence and intensity of Ixodes ricinus ticks (Acari: Ixodidae) in farmland in southern England

The present study aimed to assess whether agri-environment field margins provide a habitat for the sheep/deer tick Ixodes ricinus. Field studies were conducted in arable farmland in southern England in both extant and newly constructed field margins. The presence and intensity (i.e. the mean number of nymphs per transect, excluding zeros) of questing nymphs and adult I. ricinus were compared between field margins with three adjacent habitats: woodland, hedgerow and arable land. The presence and intensity of ticks within a field margin was also compared between three ecozones: the ecotone, the margin and the crop. It was found that field margins do support I. ricinus, although the intensity of ticks was associated with field margins with adjacent woodland, with a higher tick intensity along the ecotonal ecozone, compared with the rest of the margin or the crop edge. The presence of a hedge also increased the likelihood of finding questing nymphs in a field margin compared with a margin adjacent to arable land. This effect, however, was less pronounced than in field margins with adjacent woodland. The provision of footpaths within the margin (at least 1-2 m from the ecotone), or on the edge of the crop where paths run next to woodland known to be an important tick habitat, could be promoted to minimize tick exposure. In addition, based on the results of the present study, raising awareness that walking alongside woodlands also constitutes a tick risk could be promoted.

Living with liver flukes: Does migration matter?

Migration is typically thought to be an evolved trait driven by responses to forage or predation, but recent studies have demonstrated avoidance of parasitism can also affect success of migratory tactics within a population. We evaluated hypotheses of how migration alters parasite exposure in a partially migratory elk (Cervus canadensis) population in and adjacent to Banff National Park, Alberta, Canada. Equal numbers of elk remain year-round on the winter range or migrate to summer range. We quantified diversity and abundance of parasites in faecal elk pellets, and prevalence (number of infected individuals) and intensity (egg counts) of giant liver fluke eggs (Fascioloides magna) in faeces across migratory tactics. We tested whether giant liver fluke intensity in faeces was affected by elk use of wetlands, elevation, forage biomass, and elk concentration in the previous summer. We rejected the "migratory escape" hypothesis that suggests migration allowed elk to escape parasite exposure because migrant elk had the highest richness and evenness of parasite groups. We also rejected the hypothesis that prevalence was highest at highest summer densities because higher-density resident elk had the lowest diversity and giant liver fluke egg presence and intensity. Instead, the high prevalence and intensity of giant liver flukes in migrants was consistent with both the hypothesis of "environmental tracking", because elk that migrated earlier may expose themselves to favourable parasite conditions, and with the "environmental sampling" hypothesis, because giant liver fluke intensity increased with increased exposure to secondary host habitat (i.e., wetland). Our results indicate that differential exposure of different migratory tactics that leave the winter range has a greater influence on parasites than the concentration of elk that reside on the winter range year-round.

A unifying framework for the transient parasite dynamics of migratory hosts

Migrations allow animals to track seasonal changes in resources, find mates, and avoid harsh climates, but these regular, long-distance movements also have implications for parasite dynamics and animal health. Migratory animals have been dubbed "superspreaders" of infection, but migration can also reduce parasite burdens within host populations via migratory escape from contaminated habitats and transmission hotspots, migratory recovery due to parasite mortality, and migratory culling of infected individuals. Here, we show that a single migratory host-macroparasite model can give rise to these different phenomena under different parametrizations, providing a unifying framework for a mechanistic understanding of the parasite dynamics of migratory animals. Importantly, our model includes the impact of parasite burden on host movement capability during migration, which can lead to "parasite-induced migratory stalling" due to a positive feedback between increasing parasite burdens and reduced movement. Our results provide general insight into the conditions leading to different health outcomes in migratory wildlife. Our approach lays the foundation for tactical models that can help understand, predict, and mitigate future changes of disease risk in migratory wildlife that may arise from shifting migratory patterns, loss of migratory behavior, or climate effects on parasite development, mortality, and transmission.

Recovery from infection is more likely to favour the evolution of migration than social escape from infection

Pathogen and parasite infections are increasingly recognized as powerful drivers of animal movement, including migration. Yet, infection-related migration benefits can result from a combination of environmental and/or social conditions, which can be difficult to disentangle. Here, we focus on two infection-related mechanisms that can favour migration: moving to escape versus recover from infection. By directly comparing the evolution of migration in response to each mechanism, we can evaluate the likely importance of changing abiotic conditions (linked to migratory recovery) with changing social conditions (linked to migratory escape) in terms of infection-driven migration. We built a mathematical model and analysed it using numerically simulated adaptive dynamics to determine when migration should evolve for each migratory recovery and social migratory escape. We found that a higher fraction of the population migrated under migratory recovery than under social migratory escape. We also found that two distinct migratory strategies (e.g. some individuals always migrate and others only occasionally migrate) sometimes coexisted within populations with social migratory escape, but never with migratory recovery. Our results suggest that migratory recovery is more likely to promote the evolution of migratory behaviour, rather than escape from infected conspecifics (social migratory escape).

The Potential Role of Migratory Birds in the Rapid Spread of Ticks and Tick-Borne Pathogens in the Changing Climatic and Environmental Conditions in Europe

This opinion piece highlights the role of migratory birds in the spread of ticks and their role in the circulation and dissemination of pathogens in Europe. Birds with different lifestyles, i.e., non-migrants residing in a specific area, or short-, medium-, and long-distance migrants, migrating within one or several distant geographical regions are carriers of a number of ticks and tick-borne pathogens. During seasonal migrations, birds that cover long distances over a short time and stay temporarily in different habitats can introduce tick and pathogen species in areas where they have never occurred. An increase in the geographical range of ticks as well as the global climate changes affecting the pathogens, vectors, and their hosts increase the incidence and the spread of emerging tick-borne diseases worldwide. Tick infestations of birds varied between regions depends on the rhythms of tick seasonal activity and the bird migration rhythms determined by for example, climatic and environmental factors. In areas north of latitude ca. 58°N, immature Ixodes ricinus ticks are collected from birds most frequently, whereas ticks from the Hyalomma marginatum group dominate in areas below 42°N. We concluded that the prognosis of hazards posed by tick-borne pathogens should take into account changes in the migration of birds, hosts of many epidemiologically important tick species.

Host migration strategy is shaped by forms of parasite transmission and infection cost

Most studies on the evolution of migration focus on food, mates and/or climate as factors influencing these movements, whereas negative species interactions such as predators, parasites and pathogens are often ignored. Although infection and its associated costs clearly have the potential to influence migration, thoroughly studying these interactions is challenging without a solid theoretical framework from which to develop testable predictions in natural systems. Here, we aim to understand when parasites favour the evolution of migration. We develop a general model which enables us to explore a broad range of biological conditions and to capture population and infection dynamics over both ecological and evolutionary time-scales. We show that when migration evolves depends on whether the costs of migration and infection are paid in reduced fecundity or survival. Also important are the parasite transmission mode and spatiotemporal dynamics of infection and recovery (if it occurs). Finally, we find that partial migration (where only a fraction of the population migrates) can evolve but only when parasite transmission is density-dependent. Our results highlight the critical, if overlooked, role of parasites in shaping long-distance movement patterns, and suggest that infection should be considered alongside more traditional drivers of migration in both empirical and theoretical studies.

Responses of migratory species and their pathogens to supplemental feeding

Migratory animals undergo seasonal and often spectacular movements and perform crucial ecosystem services. In response to anthropogenic changes, including food subsidies, some migratory animals are now migrating shorter distances or halting migration altogether and forming resident populations. Recent studies suggest that shifts in migratory behaviour can alter the risk of infection for wildlife. Although migration is commonly assumed to enhance pathogen spread, for many species, migration has the opposite effect of lowering infection risk, if animals escape from habitats where pathogen stages have accumulated or if strenuous journeys cull infected hosts. Here, we summarize responses of migratory species to supplemental feeding and review modelling and empirical work that provides support for mechanisms through which resource-induced changes in migration can alter pathogen transmission. In particular, we focus on the well-studied example of monarch butterflies and their protozoan parasites in North America. We also identify areas for future research, including combining new technologies for tracking animal movements with pathogen surveillance and exploring potential evolutionary responses of hosts and pathogens to changing movement patterns. Given that many migratory animals harbour pathogens of conservation concern and zoonotic potential, studies that document ongoing shifts in migratory behaviour and infection risk are vitally needed.This article is part of the theme issue 'Anthropogenic resource subsidies and host-parasite dynamics in wildlife'.

Metrics matter: the effect of parasite richness, intensity and prevalence on the evolution of host migration

Parasites have long been thought to influence the evolution of migration, but precisely determining the conditions under which this occurs by quantifying costs of infection remains a challenge. Here we developed a model that demonstrates how the metric used to describe infection (richness/diversity, prevalence or intensity) shapes the prediction of whether migration will evolve. The model shows that predictions based on minimizing richness yield opposite results compared to those based on minimizing prevalence, with migration only selected for when minimizing prevalence. Consistent with these findings, empirical studies that measure parasite diversity typically find that migrants are worse off than residents, while those measuring prevalence or intensity find the opposite. Our own empirical analysis of fish parasite data finds that migrants (of all types) have higher parasite richness than residents, but with no significant difference in either prevalence or intensity.

Immune function and blood parasite infections impact stopover ecology in passerine birds

Stopovers play a crucial role for the success of migrating animals and are key to optimal migration theory. Variation in refuelling rates, stopover duration and departure decisions among individuals has been related to several external factors. The physiological mechanisms shaping stopover ecology are, however, less well understood. Here, we explore how immune function and blood parasite infections relate to several aspects of stopover behaviour in autumn migrating short- and long-distance migrating songbirds. We blood sampled individuals of six species and used an automated radio-telemetry system in the stopover area to subsequently quantify stopover duration, 'bush-level' activity patterns (~ 0.1-30 m), landscape movements (~ 30-6000 m), departure direction and departure time. We show that complement activity, the acute phase protein haptoglobin and blood parasite infections were related to prolonged stopover duration. Complement activity (i.e., lysis) and total immunoglobulins were negatively correlated with bush-level activity patterns. The differences partly depended on whether birds were long-distance or short-distance migrants. Birds infected with avian malaria-like parasites showed longer landscape movements during the stopover than uninfected individuals, and birds with double blood parasite infections departed more than 2.5 h later after sunset/sunrise suggesting shorter flight bouts. We conclude that variation in baseline immune function and blood parasite infection status affects stopover ecology and helps explain individual variation in stopover behaviour. These differences affect overall migration speed, and thus can have significant impact on migration success and induce carry-over effects on other annual-cycle stages. Immune function and blood parasites should, therefore, be considered as important factors when applying optimal migration theory.

Partial migration in savanna elephant populations distributed across southern Africa

Migration is an important, but threatened ecological process. Conserving migration requires the maintenance of functional connectivity across sufficiently large areas. Therefore, we need to know if, where and why species migrate. Elephants are highly mobile and can travel long distances but we do not know if they migrate. Here, we analysed the movement trajectories of 139 savanna elephants (Loxodonta africana) within eight clusters of protected areas across southern Africa to determine if elephants migrate, and if so, where, how and why they migrate. Only 25 of these elephants migrated. Elephants are a facultative partially migratory species, where only some individuals in a population migrate opportunistically, and not every year. Elephants migrated between distinct seasonal ranges corresponding to southern Africa’s dry and wet seasons. The timing of wet season migrations was associated with the onset of rainfall and the subsequent greening up of forage. Conversely, the duration, distance, and the timing of dry season migrations varied idiosyncratically. The drivers of elephant migration are likely a complex interaction between individual traits, density, and the distribution and availability of resources. Despite most migrations crossing administrative boundaries, conservation networks provided functional space for elephants to migrate.

How mammals stay healthy in nature: the evolution of behaviours to avoid parasites and pathogens

Mammals live and thrive in environments presenting ongoing threats from parasites in the form of biting flies, ticks and intestinal worms and from pathogens as wound contaminants and agents of infectious disease. Several strategies have evolved that enable animals to deal with parasites and pathogens, including eliminating away from the sleeping-resting areas, use of an array of grooming techniques, use of saliva in licking, and consuming medicinal plant-based compounds. These strategies all are species-specific and reflect the particular environment that the animal inhabits.This article is part of the Theo Murphy meeting issue 'Evolution of pathogen and parasite avoidance behaviours'.

Infections on the move: how transient phases of host movement influence disease spread

Animal movement impacts the spread of human and wildlife diseases, and there is significant interest in understanding the role of migrations, biological invasions and other wildlife movements in spatial infection dynamics. However, the influence of processes acting on infections during transient phases of host movement is poorly understood. We propose a conceptual framework that explicitly considers infection dynamics during transient phases of host movement to better predict infection spread through spatial host networks. Accounting for host transient movement captures key processes that occur while hosts move between locations, which together determine the rate at which hosts spread infections through networks. We review theoretical and empirical studies of host movement and infection spread, highlighting the multiple factors that impact the infection status of hosts. We then outline characteristics of hosts, parasites and the environment that influence these dynamics. Recent technological advances provide disease ecologists unprecedented ability to track the fine-scale movement of organisms. These, in conjunction with experimental testing of the factors driving infection dynamics during host movement, can inform models of infection spread based on constituent biological processes.

Infections with Bartonella spp. in free-ranging cervids and deer keds (Lipoptena cervi) in Norway

Bartonella bacteria are arthropod-borne and can cause long-term bacteremia in humans and animals. The predominant arthropod vectors and the mode of transmission for many novel Bartonella species remain elusive or essentially unstudied. The aim of this study was to investigate the prevalence of Bartonella spp. in Norwegian cervids and deer keds (Lipoptena cervi) and to characterise the bacteria by sequencing of the partial gltA gene and 16 S-23 S rRNA intergenic spacer region (ITS) in order to evaluate a possible transmission route. A total of 260 spleen samples and 118 deer keds were collected from cervids by hunters in the Southern part of Norway. Bartonella DNA was detected in 10.5% of spleen samples of roe deer (n = 67), in 35.1% red deer (n = 37), in 35.9% moose (n = 156), and in 85% pools of adult wingless deer ked (n = 59). Two Bartonella lineages were identified based on phylogenetic analysis of the gltA gene and ITS region sequences.

Migratory animals feel the cost of getting sick: A meta-analysis across species

Migratory animals are widely assumed to play an important role in the long-distance dispersal of parasites, and are frequently implicated in the global spread of zoonotic pathogens such as avian influenzas in birds and Ebola viruses in bats. However, infection imposes physiological and behavioural constraints on hosts that may act to curtail parasite dispersal via changes to migratory timing ("migratory separation") and survival ("migratory culling"). There remains little consensus regarding the frequency and extent to which migratory separation and migratory culling may operate, despite a growing recognition of the importance of these mechanisms in regulating transmission dynamics in migratory animals. We quantitatively reviewed 85 observations extracted from 41 studies to examine how both infection status and infection intensity are related to changes in body stores, refuelling rates, movement capacity, phenology and survival in migratory hosts across taxa. Overall, host infection status was weakly associated with reduced body stores, delayed migration and lower survival, and more strongly associated with reduced movement. Infection intensity was not associated with changes to host body stores, but was associated with moderate negative effects on movement, phenology and survival. In conclusion, we found evidence for negative effects of infection on host phenology and survival, but the effects were relatively small. This may have implications for the extent to which migratory separation and migratory culling act to limit parasite dispersal in migratory systems. We propose a number of recommendations for future research that will further advance our understanding of how migratory separation and migratory culling may shape host-parasite dynamics along migratory routes globally.

Are Migratory Animals Superspreaders of Infection?

Migratory animals are simultaneously challenged by the physiological demands of long-distance movements and the need to avoid natural enemies including parasites and pathogens. The potential for animal migrations to disperse pathogens across large geographic areas has prompted a growing body of research investigating the interactions between migration and infection. However, the phenomenon of animal migration is yet to be incorporated into broader theories in disease ecology. Because migrations may expose animals to a greater number and diversity of pathogens, increase contact rates between hosts, and render them more susceptible to infection via changes to immune function, migration has the potential to generate both "superspreader species" and infection "hotspots". However, migration has also been shown to reduce transmission in some species, by facilitating parasite avoidance ("migratory escape") and weeding out infected individuals ("migratory culling"). This symposium was convened in an effort to characterize more broadly the role that animal migrations play in the dynamics of infectious disease, by integrating a range of approaches and scales across host taxa. We began with questions related to within-host processes, focusing on the consequences of nutritional constraints and strenuous movement for individual immune capability, and of parasite infection for movement capacity. We then scaled-up to between-host processes to identify what types, distances, or patterns of host movements are associated with the spread of infectious agents. Finally, we discussed landscape-scale relationships between migration and infectious disease, and how these may be altered as a result of anthropogenic changes to climate and land use. We are just beginning to scratch the surface of the interactions between infection and animal migrations; yet, with so many migrations now under threat, there is an urgent need to develop a holistic understanding of the potential for migrations to both increase and reduce infection risk.

Seasonal variation of bat-flies (Diptera: Streblidae) in four bat species from a tropical dry forest

Seasonality of climate promotes differences in abundance and species composition of parasites, affecting host-parasite interactions. Studies have reported seasonal variation in bat-flies, which are obligate bat ectoparasites. We characterized the bat-fly load of three insectivores [Pteronotus davyi (Gray), Pteronotus parnellii (Gray) and Pteronotus personatus (Wagner)] and one nectarivorous [Leptonycteris yerbabuenae (Martínez and Villa-R.)] bat species in a tropical dry forest to test the existence of seasonality in response to the availability of resources during the wet and dry seasons. We collected 3710 bat-fly specimens belonging to six species and two genera from 497 bats. Most of the ectoparasite load parameters examined (mean abundance, mean intensity, richness, etc.), including comparisons among reproductive conditions and sex of the host, were similar in both seasons. Prevalence was the parameter that varied the most between seasons. The six bat-fly species were found in all bat species except P. personatus. The latter species and L. yerbabuenae had four and five bat-fly species in the wet and dry seasons, respectively. This study provides significant information of ectoparasites ecology in relation to seasonality, contributes to the understanding of host-parasite relationships in tropical dry forests and discusses the relevance of the abiotic and biotic factors that could impact host-parasite interactions.

The effects of seasonality on host-bat fly ecological networks in a temperate mountain cave

Changes in the specialization of parasite-host interactions will be influenced by variations in host species composition. We evaluated this hypothesis by comparing the composition of bats and bat flies within a roost cave over one annual. Five bat and five bat fly species occupied the cave over the course of the study. Bat species composition was 40% different in the rainy season compared with the dry-cold and dry-warm seasons. Despite the incorporation of three new bat species into the cave during the rainy season, bat fly species composition was not affected by seasonality, since the bats that arrived in the rainy season only contributed one new bat fly species at a low prevalence. Bat-bat fly ecological networks were less specialized in the rainy season compared with the dry-cold and dry-warm seasons because of the increase of host overlap among bat fly species during this season. This study suggests that seasonality promote: (1) differences in host species composition, and (2) a reduction in the specialization of host-parasite ecological networks.

Contrasting emergence of Lyme disease across ecosystems

Global environmental changes are causing Lyme disease to emerge in Europe. The life cycle of Ixodes ricinus, the tick vector of Lyme disease, involves an ontogenetic niche shift, from the larval and nymphal stages utilizing a wide range of hosts, picking up the pathogens causing Lyme disease from small vertebrates, to the adult stage depending on larger (non-transmission) hosts, typically deer. Because of this complexity the role of different host species for emergence of Lyme disease remains controversial. Here, by analysing long-term data on incidence in humans over a broad geographical scale in Norway, we show that both high spatial and temporal deer population density increase Lyme disease incidence. However, the trajectories of deer population sizes play an overall limited role for the recent emergence of the disease. Our study suggests that managing deer populations will have some effect on disease incidence, but that Lyme disease may nevertheless increase as multiple drivers are involved.

Environmental change is thought to have driven the recent emergence of Lyme disease in Europe. Using a decade of human disease incidence data across a large area in Norway, Mysterud et al. show that incidence correlates with deer population, but that deer population plays a limited role in recent disease emergence.