Sick without signs. Subclinical infections reduce local movements, alter habitat selection, and cause demographic shifts

In wildlife populations, parasites often go unnoticed, as infected animals appear asymptomatic. However, these infections can subtly alter behaviour. Field evidence of how these subclinical infections induce changes in movement behaviour is scarce in free-ranging animals, yet it may be crucial for zoonotic disease surveillance. We used an ultra-high-resolution tracking system (ATLAS) to monitor the movements of 60 free-ranging swallows every 8 seconds across four breeding seasons, resulting in over 1 million localizations. About 40% of these swallows were naturally infected with haemosporidian parasites. Here, we show that infected individuals had reduced foraging ranges, foraged in lower quality habitats, and faced a lowered survival probability, with an average reduction of 7.4%, albeit with some variation between species and years. This study highlights the impact of subclinical infections on movement behaviour and survival, emphasizing the importance of considering infection status in movement ecology. Our findings provide insights into individual variations in behaviour and previously unobservable local parasite transmission dynamics.

Communities of metazoan parasites in seven sympatric skate species (Elasmobranchii, Rajidae) from the English Channel and Celtic Sea differing in conservation status

Elasmobranch populations are in steep decline mainly due to overfishing bycatch, but parasites may accelerate the collapse of vulnerable and/or highly parasitized species. We therefore studied metazoan parasites of Rajidae from the northeast Atlantic: vulnerable Leucoraja fullonica, near-threatened Raja brachyura, Raja clavata, Raja microocellata and Raja undulata, and least-concerned Raja montagui and Leucoraja naevus. Overall prevalence varied from 19% for R. montagui to 100% for L. fullonica. Parasite communities differed between skate species, and prevalence and abundance were higher for L. fullonica, R. microocellata, and R. undulata. We recorded 11 parasite taxa in the study: three nematodes, six cestodes, one monogenean, and one myxosporean. Whatever the skate species, the parasite component community comprised at least two nematode taxa among Phocanema spp., Proleptus sp. and Anisakis simplex. DNA-sequencing revealed that Phocanema azarasi and Phocanema krabbei both occurred in R. microocellata and R. undulata. Phocanema spp. was first recorded in L. fullonica, L. naevus, R. microocellata, R. montagui, and R. undulata, as Proleptus sp. in L. fullonica, and A. simplex in L. fullonica and R. clavata, Rockacestus sp. and Nybelinia sp. in R. undulata, and gill-myxosporeans on L. fullonica, L. naevus, R. microocellata, and R. undulata. The occurrence of 16 new host-parasite associations suggests potential environmental changes. Information provided by trophically transmitted helminths confirmed an opportunistic skate diet based on crustaceans and fish. We discuss results in terms of host fitness loss, bioindicator role of parasites, and anisakiasis risk. We recommend incorporating parasitology in research to improve elasmobranch conservation.

Natural parasites in conjunction with behavioral and color traits explain male agonistic behaviors in a lizard

Male competition conforms to a cost-benefit model, because while aggression may increase reproductive prospects, it can also increase the risk of injury. We hypothesize that an additional cost in aggressive males would be an increase in parasite load associated with a high energy investment into sexual competition. Some of these infections, in turn, may downmodulate the level of host aggression via energetic trade-offs. We staged dyadic male contests in the lab to investigate the relationships of multiple parasites with the agonistic behavior of lizard hosts, Sceloporus occidentalis. We also included both color and behavioral traits from opponents in the analyses because (1) color patches of lizards may serve as intraspecific signals used by conspecifics to assess the quality of opponents, and (2) contests between male lizards fit classical models of escalated aggression, where lizards increase aggression displays in response to an opponent's behavior. The results conform to our hypothesis because male lizards displayed more pushups when they had more ticks. Moreover, some parasites may modulate the levels of aggression because lizards infected by hematic coccidians performed fewer pushups. Interestingly, lizards also displayed fewer pushups when both the chroma and size of the opponent's blue patch were greater. The results thus also supported the role of the blue patch of S. occidentalis as a sexual armament, because it contributed to the deterrence of aggression from opponent lizards. We revealed that natural parasitic infections in lizard hosts can contribute to their agonistic behavior. We encourage future studies to account for parasites in behavioral tests with lizards.

Implications of biotic factors for toxicity testing in laboratory studies

There is an emerging call from scientists globally to advance the environmental relevance of laboratory studies, particularly within the field of ecotoxicology. To answer this call, we must carefully examine and elucidate the shortcomings of standardized toxicity testing methods that are used in the derivation of toxicity values and regulatory criteria. As a consequence of rapidly accelerating climate change, the inclusion of abiotic co-stressors are increasingly being incorporated into toxicity studies, with the goal of improving the representativeness of laboratory-derived toxicity values used in ecological risk assessments. However, much less attention has been paid to the influence of biotic factors that may just as meaningfully impact our capacity to evaluate and predict risks within impacted ecosystems. Therefore, the overarching goal is to highlight key biotic factors that should be taken into consideration during the experimental design and model selection phase. SYNOPSIS: Scientists are increasingly finding that lab reared results in toxicology might not be reflective of the external wild environment, we highlight in this review some key considerations when working between the lab and field.

Accelerometer-based detection of African swine fever infection in wild boar

Infectious wildlife diseases that circulate at the interface with domestic animals pose significant threats worldwide and require early detection and warning. Although animal tracking technologies are used to discern behavioural changes, they are rarely used to monitor wildlife diseases. Common disease-induced behavioural changes include reduced activity and lethargy ('sickness behaviour'). Here, we investigated whether accelerometer sensors could detect the onset of African swine fever (ASF), a viral infection that induces high mortality in suids for which no vaccine is currently available. Taking advantage of an experiment designed to test an oral ASF vaccine, we equipped 12 wild boars with an accelerometer tag and quantified how ASF affects their activity pattern and behavioural fingerprint, using overall dynamic body acceleration. Wild boars showed a daily reduction in activity of 10-20% from the healthy to the viremia phase. Using change point statistics and comparing healthy individuals living in semi-free and free-ranging conditions, we show how the onset of disease-induced sickness can be detected and how such early detection could work in natural settings. Timely detection of infection in animals is crucial for disease surveillance and control, and accelerometer technology on sentinel animals provides a viable complementary tool to existing disease management approaches.

Adaptive host responses to infection can resemble parasitic manipulation

Using a dynamic optimisation model for juvenile fish in stochastic food environments, we investigate optimal hormonal regulation, energy allocation and foraging behaviour of a growing host infected by a parasite that only incurs an energetic cost. We find it optimal for the infected host to have higher levels of orexin, growth and thyroid hormones, resulting in higher activity levels, increased foraging and faster growth. This growth strategy thus displays several of the fingerprints often associated with parasite manipulation: higher levels of metabolic hormones, faster growth, higher allocation to reserves (i.e. parasite-induced gigantism), higher risk-taking and eventually higher predation rate. However, there is no route for manipulation in our model, so these changes reflect adaptive host compensatory responses. Interestingly, several of these changes also increase the fitness of the parasite. Our results call for caution when interpreting observations of gigantism or risky host behaviours as parasite manipulation without further testing.

Animal movement and associated infectious disease risk in a metapopulation

Animal movements among habitat patches or populations are important for maintaining long-term genetic and demographic viability, but connectivity may also facilitate disease spread and persistence. Understanding factors that influence animal movements is critical to understanding potential transmission risk and persistence of communicable disease in spatially structured systems. We evaluated effects of sex, age and Mycoplasma ovipneumoniae infection status at capture on intermountain movements and seasonal movement rates observed in desert bighorn sheep (Ovis canadensis nelsoni) using global positioning system collar data from 135 individuals (27 males, 108 females) in 14 populations between 2013 and 2018, following a pneumonia outbreak linked to the pathogen M. ovipneumoniae in the Mojave Desert, California, USA. Based on logistic regression analysis, intermountain movements were influenced by sex, age and most notably, infection status at capture: males, older animals and uninfected individuals were most likely to make such movements. Based on multiple linear regression analysis, females that tested positive for M. ovipneumoniae at capture also had lower mean daily movement rates that were further influenced by season. Our study provides empirical evidence of a pathogenic infection decreasing an individual's future mobility, presumably limiting that pathogen's ability to spread, and ultimately influencing transmission risk within a spatially structured system.

The effects of Contracaecum osculatum larvae on the growth of Atlantic cod (Gadus morhua)

Atlantic cod (Gadus morhua) from the Eastern Baltic stock have decreased in numbers and condition since the 1990′s. Among several causes, an increased prevalence and intensity of the nematode Contracaecum osculatum has been discussed. This increase has been attributed to a population increase of the parasites final host, the grey seal (Halichoerus grypus). Other studies have looked at the role of Contracaecum osculatum on cod growth and condition on recently caught cod, or done short term experimental studies in lab. This study instead investigated the importance of Contracaecum osculatum for cod growth in a sea pen based experiment, where cod were kept and fed in order to monitor growth. The results show that a higher density (number of nematodes per gram liver) decreases cod growth potential. If the number of nematodes exceeded 8 per gram liver cod did not grow in length, even when given generous amounts of food. Accounting for the lack of growth due to Contracaecum osculatum may improve stock assessments and increase the possibility to reach management targets.

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High C. osculatum density limits cod growth potential, even if generously fed.

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A higher C. osculatum density result in less, and at a point no growth in weight.

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If exceeding eight C. osculatum per gram liver, cod do not grow in length.

Experimental removal of nematode parasites increases growth, sprint speed, and mating success in brown anole lizards

Parasites interact with nearly all free-living organisms and can impose substantial fitness costs by reducing host survival, mating success, and fecundity. Parasites may also indirectly affect host fitness by reducing growth and performance. However, experimentally characterizing these costs of parasitism is challenging in the wild because common antiparasite drug formulations require repeated dosing that is difficult to implement in free-living populations, and because the extended-release formulations that are commercially available for livestock and pets are not suitable for smaller animals. To address these challenges, we developed a method for the long-term removal of nematode parasites from brown anole lizards (Anolis sagrei) using an extended-release formulation of the antiparasite drug ivermectin. This treatment eliminated two common nematode parasites in captive adult males and dramatically reduced the prevalence and intensity of infection by these parasites in wild adult males and females. Experimental parasite removal significantly increased the sprint speed of captive adult males, the mating success of wild adult males, and the growth of wild juveniles of both sexes. Although parasite removal did not have any effect on survival in wild anoles, parasites may influence fitness directly through reduced mating success and indirectly through reduced growth and performance. Our method of long-term parasite manipulation via an extended-release formulation of ivermectin should be readily adaptable to many other small vertebrates, facilitating experimental tests of the extent to which parasites affect host phenotypes, fitness, and eco-evolutionary dynamics in the wild.

Increased parasite load is associated with reduced metabolic rates and escape responsiveness in pumpkinseed sunfish

Wild animals have parasites that can compromise their physiological and/or behavioural performance. Yet, the extent to which parasite load is related to intraspecific variation in performance traits within wild populations remains relatively unexplored. We used pumpkinseed sunfish (Lepomis gibbosus) and their endoparasites as a model system to explore the effects of infection load on host aerobic metabolism and escape performance. Metabolic traits (standard and maximum metabolic rates, aerobic scope) and fast-start escape responses following a simulated aerial attack by a predator (responsiveness, response latency, and escape distance) were measured in fish from across a gradient of visible (i.e. trematodes causing black spot disease counted on fish surfaces) and non-visible (i.e. cestodes in fish abdominal cavity counted post-mortem) endoparasite infection. We found that a higher infection load of non-visible endoparasites was related to lower standard and maximum metabolic rates, but not aerobic scope in fish. Non-visible endoparasite infection load was also related to decreased responsiveness of the host to a simulated aerial attack. Visible endoparasites were not related to changes in metabolic traits nor fast-start escape responses. Our results suggest that infection with parasites that are inconspicuous to researchers can result in intraspecific variation in physiological and behavioral performance in wild populations, highlighting the need to more explicitly acknowledge and account for the role played by natural infections in studies of wild animal performance.

Inter-individual variation in parasite manipulation of host phenotype: A role for parasite microbiomes?

Alterations in host phenotype induced by metazoan parasites are widespread in nature, yet the underlying mechanisms and the sources of intraspecific variation in the extent of those alterations remain poorly understood. In light of the microbiome revolution sweeping through ecology and evolutionary biology, we hypothesise that the composition of symbiotic microbial communities living within individual parasites influences the nature and extent of their effect on host phenotype. The interests of both the parasite and its symbionts are aligned through the latter's vertical transmission, favouring joint contributions to the manipulation of host phenotype. Our hypothesis can explain the variation in the extent to which parasites alter host phenotype, as microbiome composition varies among individual parasites. We propose two non-exclusive approaches to test the hypothesis, furthering the integration of microbiomes into studies of host-parasite interactions.

Energetic costs of ectoparasite infection in Atlantic salmon

Parasites are widespread in nature where they affect energy budgets of hosts, and depending on the imposed pathogenic severity, this may reduce host fitness. However, the energetic costs of parasite infections are rarely quantified. In this study, we measured metabolic rates in recently seawater adapted Atlantic salmon (Salmo salar) infected with the ectoparasitic copepod Lepeophtheirus salmonis and used an aerobic scope framework to assess the potential ecological impact of this parasite-host interaction. The early chalimus stages of L. salmonis did not affect either standard or maximum metabolic rates. However, the later mobile pre-adult stages caused an increase in both standard and maximum metabolic rate yielding a preserved aerobic scope. Notably, standard metabolic rates were elevated by 26%, presumably caused by increased osmoregulatory burdens and costs of mobilizing immune responses. The positive impact on maximum metabolic rates was unexpected and suggests that fish are able to transiently overcompensate energy production to endure the burden of parasites and thus allow for continuation of normal activities. However, infected fish are known to suffer reduced growth, and this suggests that a trade-off exists in acquisition and assimilation of resources despite of an uncompromised aerobic scope. As such, when assessing impacts of environmental or biotic factors, we suggest that elevated routine costs may be a stronger predictor of reduced fitness than the available aerobic scope. Furthermore, studying effects on parasitized fish in an ecophysiological context deserves more attention, especially considering interacting effects of other stressors in the Anthropocene.

The influence of infection status and parasitism risk on host dispersal and susceptibility to infection in Drosophila nigrospiracula

For many organisms, habitat avoidance provides the first line of defence against parasitic infection. Changes in infection status can shift the cost-benefit ratio of remaining in a given habitat vs dispersing. The aim of this study was to test the hypothesis that the propensity to disperse in Drosophila nigrospiracula is mediated by current parasite load and the risk of further infection by an ectoparasitic mite (Macrocheles subbadius). An activity monitor was used to assess dispersal propensity among infected and uninfected flies. The activity level of uninfected females increased threefold upon exposure to a mite, whereas the activity among uninfected males increased by 17-fold in the presence of a questing mite. Among infected flies, the risk of further infection also generated a change in activity, but the magnitude of the response was dependent on host sex. Current infection status influenced the probability of acquiring more parasites due to increased susceptibility to infection with mite load. The probability of acquiring additional mites among males increased more rapidly compared to female flies. Current infection status can potentially determine the risk of further infection, the host propensity and ability to disperse, with consequence for hosts and parasites at the individual, population and species level.

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.

Physiological condition of Eastern Baltic cod, Gadus morhua, infected with the parasitic nematode Contracaecum osculatum

Establishing relationships between parasite infection and physiological condition of the host can be difficult and therefore are often neglected when describing factors causing population declines. Using the parasite-host system between the parasitic nematode Contracaecum osculatum and the Eastern Baltic cod Gadus morhua, we here shed new light on how parasite load may relate to the physiological condition of a transport host. The Eastern Baltic cod is in distress, with declining nutritional conditions, disappearance of the larger fish, high natural mortality and no signs of recovery of the population. During the latest decade, high infection levels with C. osculatum have been observed in fish in the central and southern parts of the Baltic Sea. We investigated the aerobic performance, nutritional condition, organ masses, and plasma and proximate body composition of wild naturally infected G. morhua in relation to infection density with C. osculatum. Fish with high infection densities of C. osculatum had (i) decreased nutritional condition, (ii) depressed energy turnover as evidenced by reduced standard metabolic rate, (iii) reduction in the digestive organ masses, and alongside (iv) changes in the plasma, body and liver composition, and fish energy source. The significantly reduced albumin to globulin ratio in highly infected G. morhua suggests that the fish suffer from a chronic liver disease. Furthermore, fish with high infection loads had the lowest Fulton's condition factor. Yet, it remains unknown whether our results steam from a direct effect of C. osculatum, or because G. morhua in an already compromised nutritional state are more susceptible towards the parasite. Nevertheless, impairment of the physiological condition can lead to reduced swimming performance, compromising foraging success while augmenting the risk of predation, potentially leading to an increase in the natural mortality of the host. We hence argue that fish-parasite interactions must not be neglected when implementing and refining strategies to rebuild deteriorating populations.

Parasite infection directly impacts escape response and stress levels in fish

Parasites can account for a substantial proportion of the biomass in marine communities. As such, parasites play a significant ecological role in ecosystem functioning via host interactions. Unlike macropredators, such as large piscivores, micropredators, such as parasites, rarely cause direct mortality. Rather, micropredators impose an energetic tax, thus significantly affecting host physiology and behaviour via sublethal effects. Recent research suggests that infection by gnathiid isopods (Crustacea) causes significant physiological stress and increased mortality rates. However, it is unclear whether infection causes changes in the behaviours that underpin escape responses or changes in routine activity levels. Moreover, it is poorly understood whether the cost of gnathiid infection manifests as an increase in cortisol. To investigate this, we examined the effect of experimental gnathiid infection on the swimming and escape performance of a newly settled coral reef fish and whether infection led to increased cortisol levels. We found that micropredation by a single gnathiid caused fast-start escape performance and swimming behaviour to significantly decrease and cortisol levels to double. Fast-start escape performance is an important predictor of recruit survival in the wild. As such, altered fitness-related traits and short-term stress, perhaps especially during early life stages, may result in large scale changes in the number of fish that successfully recruit to adult populations.

Schistocephalus parasite infection alters sticklebacks' movement ability and thereby shapes social interactions

Parasitism is ubiquitous in the animal kingdom. Although many fundamental aspects of host-parasite relationships have been unravelled, few studies have systematically investigated how parasites affect organismal movement. Here we combine behavioural experiments of Schistocephalus solidus infected sticklebacks with individual-based simulations to understand how parasitism affects individual movement ability and thereby shapes social interaction patterns. High-resolution tracking revealed that infected fish swam, accelerated, and turned more slowly than did non-infected fish, and tended to be more predictable in their movements. Importantly, the strength of these effects increased with increasing parasite load (proportion of body weight), with more heavily infected fish showing larger changes and impairments in behaviour. When grouped, pairs of infected fish moved more slowly, were less cohesive, less aligned, and less temporally coordinated than non-infected pairs, and mixed pairs were primarily led by the non-infected fish. These social patterns also emerged in simulations of self-organised groups composed of individuals differing similarly in speed and turning tendency, suggesting infection-induced changes in mobility and manoeuvrability may drive collective outcomes. Together, our results demonstrate how infection with a complex life-cycle parasite affects the movement ability of individuals and how this in turn shapes social interaction patterns, providing important mechanistic insights into the effects of parasites on host movement dynamics.

Host age predicts parasite occurrence, richness, and nested infracommunities in a pilot whale-helminth network

Ecological data on marine mammal parasites represent an excellent opportunity to expand our understanding of host-parasite systems. In this study, we used a dataset of intestinal helminth parasites on 167 long-finned pilot whales Globicephala melas (Traill, 1809) from seven localities in the Faroe Islands to evaluate the extent to which the host's age and sex influence the occurrence, richness, and nested pattern of helminth parasites and the importance of individual hosts to the helminth community. We found positive effects of age on both the occurrence and richness of helminths. Older host individuals showed an ordered accumulation of parasites, as evidenced by the nested pattern in their composition. Males had a higher occurrence of parasites than females, but the richness of helminths did not differ between sexes. Our findings suggest that differences in host-parasite interactions in long-finned pilot whales result mainly from age-structured variations in biological and behavioral characteristics.

Magnitude and direction of parasite-induced phenotypic alterations: a meta-analysis in acanthocephalans

Several parasite species have the ability to modify their host's phenotype to their own advantage thereby increasing the probability of transmission from one host to another. This phenomenon of host manipulation is interpreted as the expression of a parasite extended phenotype. Manipulative parasites generally affect multiple phenotypic traits in their hosts, although both the extent and adaptive significance of such multidimensionality in host manipulation is still poorly documented. To review the multidimensionality and magnitude of host manipulation, and to understand the causes of variation in trait value alteration, we performed a phylogenetically corrected meta-analysis, focusing on a model taxon: acanthocephalan parasites. Acanthocephala is a phylum of helminth parasites that use vertebrates as final hosts and invertebrates as intermediate hosts, and is one of the few parasite groups for which manipulation is predicted to be ancestral. We compiled 279 estimates of parasite-induced alterations in phenotypic trait value, from 81 studies and 13 acanthocephalan species, allocating a sign to effect size estimates according to the direction of alteration favouring parasite transmission, and grouped traits by category. Phylogenetic inertia accounted for a low proportion of variation in effect sizes. The overall average alteration of trait value was moderate and positive when considering the expected effect of alterations on trophic transmission success (signed effect sizes, after the onset of parasite infectivity to the final host). Variation in the alteration of trait value was affected by the category of phenotypic trait, with the largest alterations being reversed taxis/phobia and responses to stimuli, and increased vulnerability to predation, changes to reproductive traits (behavioural or physiological castration) and immunosuppression. Parasite transmission would thereby be facilitated mainly by changing mainly the choice of micro-habitat and the anti-predation behaviour of infected hosts, and by promoting energy-saving strategies in the host. In addition, infection with larval stages not yet infective to definitive hosts (acanthella) tends to induce opposite effects of comparable magnitude to infection with the infective stage (cystacanth), although this result should be considered with caution due to the low number of estimates with acanthella. This analysis raises important issues that should be considered in future studies investigating the adaptive significance of host manipulation, not only in acanthocephalans but also in other taxa. Specifically, the contribution of phenotypic traits to parasite transmission and the range of taxonomic diversity covered deserve thorough attention. In addition, the relationship between behaviour and immunity across parasite developmental stages and host-parasite systems (the neuropsychoimmune hypothesis of host manipulation), still awaits experimental evidence. Most of these issues apply more broadly to reported cases of host manipulation by other groups of parasites.

The energetic cost of parasitism in a wild population

Parasites have profound fitness effects on their hosts, yet these are often sub-lethal, making them difficult to understand and quantify. A principal sub-lethal mechanism that reduces fitness is parasite-induced increase in energetic costs of specific behaviours, potentially resulting in changes to time and energy budgets. However, quantifying the influence of parasites on these costs has not been undertaken in free-living animals. We used accelerometers to estimate energy expenditure on flying, diving and resting, in relation to a natural gradient of endo-parasite loads in a wild population of European shags Phalacrocorax aristotelis. We found that flight costs were 10% higher in adult females with higher parasite loads and these individuals spent 44% less time flying than females with lower parasite loads. There was no evidence for an effect of parasite load on daily energy expenditure, suggesting the existence of an energy ceiling, with the increase in cost of flight compensated for by a reduction in flight duration. These behaviour specific costs of parasitism will have knock-on effects on reproductive success, if constraints on foraging behaviour detrimentally affect provisioning of young. The findings emphasize the importance of natural parasite loads in shaping the ecology and life-history of their hosts, which can have significant population level consequences.

Low intensity blood parasite infections do not reduce the aerobic performance of migratory birds

Blood parasites (Haemosporidia) are thought to impair the flight performance of infected animals, and therefore, infected birds are expected to differ from their non-infected counterparts in migratory capacity. Since haemosporidians invade host erythrocytes, it is commonly assumed that infected individuals will have compromised aerobic capacity, but this has not been examined in free-living birds. We tested if haemosporidian infections affect aerobic performance by examining metabolic rates and exercise endurance in migratory great reed warblers (Acrocephalus arundinaceus) experimentally treated with Plasmodium relictum pGRW04 and in naturally infected wild birds over consecutive life-history stages. We found no effect of acute or chronic infections on resting metabolic rate, maximum metabolic rate or exercise endurance in either experimentally treated or free-living birds. Oxygen consumption rates during rest and while undergoing maximum exercise as well as exercise endurance increased from breeding to migration stages in both infected and non-infected birds. Importantly, phenotypic changes associated with preparation for migration were similarly unaffected by parasitaemia. Consequently, migratory birds experiencing parasitaemia levels typical of chronic infection do not differ in migratory capacity from their uninfected counterparts. Thus, if infected hosts differ from uninfected conspecifics in migration phenology, other mechanisms besides aerobic capacity should be considered.

Endoparasite and nutritional status of Suffolk lambs in seven production systems

Lambs are the most susceptible category for parasite infections; therefore, the choice of the production system can influence nutritional status and reduce parasite infections. The present study aimed to evaluate the endoparasites and nutritional status of meat lambs in seven production systems. In the feedlot, they were (S1) early weaned lambs in feedlot and (S2) unweaned lambs in feedlot with controlled suckling. On pasture, they were (S3) early weaned lambs on pasture without supplementation, (S4) early weaned lambs on pasture with concentrate supplementation post-weaning, (S5) unweaned and unsupplemented lambs on pasture, (S6) unweaned lambs on pasture with concentrate supplementation and creep-feeding and (S7) unweaned lambs on pasture with free access to creep-grazing on white clover (Trifolium repens). Suffolk lambs (n = 132) were evaluated from 45 to 101 days of age, at 14-day intervals (0, 14, 28, 42 and 56 days). Parasite faecal egg count (FEC), FAMACHA score (FMC), average daily weight-gain and body condition score (BCS) were evaluated. The animals were treated with anthelmintics when they had FMC 3, 4 or 5 and/or FEC above 700. BCS and FEC (r = –0.361) and BCS and FMC variables (r = –0.313) were negatively correlated (P ≤ 0.01). FEC was lower in feedlot and in creep-feeding animals than in the other systems after the second evaluation (28 days). The weaned feedlot-lamb and controlled-suckling systems presented the best performance. On pasture, the animals in creep-feeding and creep-grazing had the best performance. Weaned and unsupplemented lambs on pasture had the lowest daily weight-gain (63 g/day) and the highest FMC scores (43% of animals) and the lowest BCS (mean 1.5). The endoparasite and nutritional statuses of the lambs were strongly correlated and were influenced by the production system, mainly when the ewes were present and the lambs received supplementation on pasture.

Helminth infections in a pair of sympatric congeneric lizard species

We analyzed parameters of parasitism by helminths in a pair of sympatric congeneric lizard species (Tropidurus hispidus and Tropidurus semitaeniatus). Differences in their supracommunities (richness, composition, and abundance) and the influence of helminthic loads on minimum flight initiation distances and body temperatures were evaluated. We reported new findings of Piratuba digiticauda infecting T. hispidus and Oochoristica bresslaui infecting T. semitaeniatus. Parapharyngodon alvarengai was the most abundant helminth in both host species. Tropidurus hispidus individuals hosted a higher abundance and richness of helminths than T. semitaeniatus, with females of the former having larger helminthic loads than males. Dissimilarities between host species may be attributed to differences in their utilization of niche dimensions (time, food, and structural and thermal space), the occurrence of morphological differences that result in differential exposure to the sources and agents of infection, and/or differential immunological functions. Our data suggests that infection by P. alvarengai led to some limitations in locomotor performance of T. hispidus resulting in decreased minimum flight initiation distance as infection rates increased. Individuals opted for a prolonged period of immobility to avoid capture. There was a negative relationship between helminthic loads and body temperatures in T. semitaeniatus, possibly due to decreased activity and thermoregulation rates, and increased use of shelters by lizards with high infection levels to avoid predation.

Prevalence of Ostertagia ostertagi lesions in slaughtered dairy cattle from São Miguel Island, Azores, Portugal

Ostertagiosis caused by Ostertagia ostertagi is considered the most important parasitosis in dairy cattle raised in temperate areas. The aim of this investigation was to determinate the prevalence of ostertagiosis in cattle slaughtered in São Miguel Island (SMI), Azores, the geographical distribution of positive cases, its economic impact and farmers awareness regarding preventive and control measurements against this parasitosis. From the 2000 animals sampled, 1282 presented lesions compatible with ostertagiosis representing a prevalence of 49.0% in young animals and 75.7% in adults. Positive animals had significantly worse carcass rating when slaughtered and the fat rating of positive uncastrated males older than 24months was also significantly lower. The presence of lesions compatible with ostertagiosis resulted in a total weight loss of 2.810.89kg (2.19kg mean weight loss per animal - 1.07% carcass weight drop), which extrapolating to the total of animals slaughtered in SMI in 2014 corresponds to a value of losses of roughly about 91.000.00€. Our data also indicate that ostertagiosis has a widespread distribution throughout the Island and that 85.7% of the farmers dewormed calves and 42.9% dewormed cows (only one administration was provided for each deworming). Data shows that ostertagiosis represents an important economical lost in dairy cattle from SMI and a significant lack of knowledge by farmers about the benefits of deworming and preventive management practices.

Inter- and intraspecific conflicts between parasites over host manipulation

Host manipulation is a common strategy by which parasites alter the behaviour of their host to enhance their own fitness. In nature, hosts are usually infected by multiple parasites. This can result in a conflict over host manipulation. Studies of such a conflict in experimentally infected hosts are rare. The cestode Schistocephalus solidus (S) and the nematode Camallanus lacustris (C) use copepods as their first intermediate host. They need to grow for some time inside this host before they are infective and ready to be trophically transmitted to their subsequent fish host. Accordingly, not yet infective parasites manipulate to suppress predation. Infective ones manipulate to enhance predation. We experimentally infected laboratory-bred copepods in a manner that resulted in copepods harbouring (i) an infective C plus a not yet infective C or S, or (ii) an infective S plus a not yet infective C. An infective C completely sabotaged host manipulation by any not yet infective parasite. An infective S partially reduced host manipulation by a not yet infective C. We hence show experimentally that a parasite can reduce or even sabotage host manipulation exerted by a parasite from a different species.

Does resource availability affect host manipulation? – an experimental test with Schistocephalus solidus

Host manipulation is a common strategy of parasites employed to increase their fitness by changing the phenotype of their hosts. Whether host manipulation might be affected by environmental factors such as resource availability, has received little attention. We experimentally infected laboratory-bred copepods with the cestodeSchistocephalus solidus, submitted infected and uninfected copepods to either a high or a low food treatment, and measured their behaviour. Infection reduced host activity and speed in both feeding treatments. However, the difference between the infected and uninfected copepods was smaller under low food conditions, because uninfected, but not infected, copepods moved slower under these conditions. We suggest that these differences are mediated by the physical condition of copepods rather than changes in how strongly the parasite manipulated host behaviour. Additionally, we measured three fitness-relevant traits (growth, development and infection rate in the next host) of the parasite to identify potential trade-offs with host manipulation. The largest parasites in copepods appeared the least manipulative, i.e. their hosts showed the smallest behavioural alterations, but this may again reflect variation in copepod condition, rather than life history trade-offs between parasite growth and host manipulation. Our results point to the possibility that parasite transmission depends on environmental conditions.

Experimental Infections of Bluegill with the Trematode Ribeiroia ondatrae (Digenea: Cathaemasiidae): Histopathology and Hematological Response

Infections by the digenetic trematode, Ribeiroia ondatrae, cause severe limb malformations in many North American amphibians. Ribeiroia ondatrae also infects fishes as second intermediate hosts, but less is known about the pathology and immune responses initiated in infected fish, even though reports of infected fish date back to early 1900s. To this end, we experimentally exposed juvenile Bluegills Lepomis macrochirus to three doses of R. ondatrae cercariae and monitored the pathology, parasite infection success, and humoral responses over 648 h. All exposed fish became infected with metacercariae, and the average infection load increased with exposure dose. Histologically, infection was associated with acute hemorrhages in the lateral line and local dermis at 36 h, followed by progressive granulomatous inflammation that led to the destruction of encysted metacercariae. Correspondingly, over the course of 648 h we observed an 85% decline in average infection load among hosts, reflecting the host's clearance of the parasite. Infection was not associated with changes in fish growth or survival, but did correlate with leukocytosis and neutrophilia in circulating host blood. Understanding the physiological responses of R. ondatrae in Bluegill will help to clarify the ecological effects of this parasite and provide a foundation for subsequent comparisons into its effects on behavior, individual health, and population dynamics of Bluegill.

An experimental conflict of interest between parasites reveals the mechanism of host manipulation

Parasites can increase their host's predation susceptibility. It is a long-standing puzzle, whether this is caused by host manipulation, an evolved strategy of the parasite, or by side effects due to, for example, the parasite consuming energy from its host thereby changing the host's trade-off between avoiding predation and foraging toward foraging. Here, we use sequential infection of three-spined sticklebacks with the cestode Schistocephalus solidus so that parasites have a conflict of interest over the direction of host manipulation. With true manipulation, the not yet infective parasite should reduce rather than enhance risk taking because predation would be fatal for its fitness; if host behavior is changed by a side effect, the 2 parasites would add their increase of predation risk because both drain energy. Our results support the latter hypothesis. In an additional experiment, we tested both infected and uninfected fish either starved or satiated. True host manipulation should act independently of the fish's hunger status and continue when energy drain is balanced through satiation. Starvation and satiation affect the risk averseness of infected sticklebacks similarly to that of uninfected starved and satiated ones. Increased energy drain rather than active host manipulation dominates behavioral changes of S. solidus-infected sticklebacks.