Parasite Abundance Research Articles

How host diversity and abundance affect parasite infections: Results from a whole-ecosystem manipulation of bird activity

As environmental change drives reductions in free-living species abundance and diversity, at least two alternative pathways are possible for parasitic species. On one hand, diversity losses could drive parasite population declines or extirpations, with potentially influential effects on ecosystem processes, given parasites' ecological importance. On the other hand, host species loss could reduce the abundance of non-competent hosts that interfere with pathogen transmission or facilitate increases in the abundance of “weedy”, highly competent host species, intensifying transmission. While many experimental studies have investigated how changes in free-living species affect the fate of individual parasite species, comparatively little is known about the consequences across multiple parasite taxa within an ecosystem, limiting opportunities to assess the proportion of species that are likely to take each of the alternative pathways. Here, we present results of a before-after-control-impact (BACI) experiment conducted in central California, USA, in which we manipulated bird activity at the scale of wetland ecosystems and tracked the resulting effects on the identity and abundance of protozoan and metazoan parasites of amphibians. Of the eight common parasite taxa that constituted ~97% of parasite observations, four responded negatively to bird-augmentation treatments, two responded positively, and two exhibited no significant response. We conclude that it is possible, within a single ecosystem, for free-living species change to produce declines in some parasite species, increases in others, and no change in yet other species. Disease ecology urgently needs tools for forecasting when and where each of these effects should occur, which will facilitate management efforts focused on mitigating outbreaks of disease on one hand and preventing extinction of parasite species on the other.

Prior exposure to long-day photoperiods alters immune responses and increases susceptibility to parasitic infection in stickleback.

Seasonal disease and parasitic infection are common across organisms, including humans, and there is increasing evidence for intrinsic seasonal variation in immune systems. Changes are orchestrated through organisms' physiological clocks using cues such as day length. Ample research in diverse taxa has demonstrated multiple immune responses are modulated by photoperiod, but to date, there have been few experimental demonstrations that photoperiod cues alter susceptibility to infection. We investigated the interactions among photoperiod history, immunity and susceptibility in laboratory-bred three-spined stickleback (a long-day breeding fish) and its external, directly reproducing monogenean parasite Gyrodactylus gasterostei. We demonstrate that previous exposure to long-day photoperiods (PLD) increases susceptibility to infection relative to previous exposure to short days (PSD), and modifies the response to infection for the mucin gene muc2 and Treg cytokine foxp3a in skin tissues in an intermediate 12 L : 12 D photoperiod experimental trial. Expression of skin muc2 is reduced in PLD fish, and negatively associated with parasite abundance. We also observe inflammatory gene expression variation associated with natural inter-population variation in resistance, but find that photoperiod modulation of susceptibility is consistent across host populations. Thus, photoperiod modulation of the response to infection is important for host susceptibility, highlighting new mechanisms affecting seasonality of host–parasite interactions.

Паразитологічні дослідження в Антарктиці:огляд проблематики та перспективи

This paper provides an overview of parasitological research conducted in Antarctica, particularly near the Ukrainian Antarctic Akademik Vernadsky station. Taking into account the global climate and anthropogenic changes that lead to the destruction of natural ecosystems of the Southern ocean and the abundance of fish parasites of zoonotic significance posing a threat to human health, investigations of the animal parasite communities in the Antarctic, including in the teleost fishes, become of special relevance. Further long-term ecological and parasitological monitoring of Antarctic marine and coastal ecosystems is necessary and will allow to investigate the speed and directions of ecological changes in Antarctic marine ecosystems.

Mapping the drivers of parasitic weed abundance at a national scale: a new approach applied to Striga asiatica in the mid‐west of Madagascar

AbstractThe parasitic weed genus Striga causes huge losses to crop production in sub‐Saharan Africa, estimated to be in excess of $7 billion per year. There is a paucity of reliable distribution data for Striga; however, such data are urgently needed to understand current drivers, better target control efforts, as well as to predict future risks. To address this, we developed a methodology to enable rapid, large‐scale monitoring of Striga populations. We used this approach to uncover the factors that currently drive the abundance and distribution of Striga asiatica in Madagascar. Two long‐distance transects were established across the middle‐west region of Madagascar in which S. asiatica abundance in fields adjacent to the road was estimated. Management, crop structure and soil data were also collected. Analysis of the data suggests that crop variety, companion crop and previous crop were correlated with Striga density. A positive relationship between within‐field Striga density and the density of the nearest neighbouring fields indicates that spatial configuration and connectivity of suitable habitats is also important in determining Striga spread. Our results demonstrate that we are able to capture distribution and management data for Striga density at a landscape scale and use this to understand the ecological and agronomic drivers of abundance. The importance of crop varieties and cropping patterns is significant, as these are key socio‐economic elements of Malagasy cropping practices. Therefore, they have the potential to be promoted as readily available control options, rather than novel technologies requiring introduction.

Sulphide-toxic habitats are not refuges from parasite infections in an extremophile fish

We still have a limited understanding of why animals colonize extreme environments, but one hypothesis (the Pathogen Refuge Hypothesis, PRH) posits that they might represent a safe haven from parasites and other pathogens. We tested this idea by quantifying endoparasite infections in five populations of the neotropical freshwater fish Poecilia mexicana, three populations from toxic, H2S-rich habitats and two control populations from nearby rivers and creeks. Counter to predictions derived from the PRH, only P. mexicana from toxic habitats harboured heterophyid metacercariae in their hearts. We further uncovered differences in parasite prevalences and abundances between the three toxic habitats. Our results provide evidence against the PRH and add depth to our understanding of life in (and adaptation to) extreme environments.

Fluid preservation causes minimal reduction of parasite detectability in fish specimens: A new approach for reconstructing parasite communities of the past?

Long‐term datasets are needed to evaluate temporal patterns in wildlife disease burdens, but historical data on parasite abundance are extremely rare. For more than a century, natural history collections have been accumulating fluid‐preserved specimens, which should contain the parasites infecting the host at the time of its preservation. However, before this unique data source can be exploited, we must identify the artifacts that are introduced by the preservation process. Here, we experimentally address whether the preservation process alters the degree to which metazoan parasites are detectable in fluid‐preserved fish specimens when using visual parasite detection techniques. We randomly assigned fish of three species (Gadus chalcogrammus, Thaleichthys pacificus, and Parophrys vetulus) to two treatments. In the first treatment, fish were preserved according to the standard procedures used in ichthyological collections. Immediately after the fluid‐preservation process was complete, we performed parasitological dissection on those specimens. The second treatment was a control, in which fish were dissected without being subjected to the fluid‐preservation process. We compared parasite abundance between the two treatments. Across 298 fish individuals and 59 host–parasite pairs, we found few differences between treatments, with 24 of 27 host–parasite pairs equally abundant between the two treatments. Of these, one pair was significantly more abundant in the preservation treatment than in the control group, and two pairs were significantly less abundant in the preservation treatment than in the control group. Our data suggest that the fluid‐preservation process does not have a substantial effect on the detectability of metazoan parasites. This study addresses only the effects of the fixation and preservation process; long‐term experiments are needed to address whether parasite detectability remains unchanged in the months, years, and decades of storage following preservation. If so, ecologists will be able to reconstruct novel, long‐term datasets on parasite diversity and abundance over the past century or more using fluid‐preserved specimens from natural history collections.

Impacts of ontogenetic dietary shifts on the food-transmitted intestinal parasite communities of two lake salmonids.

Ontogenetic dietary shifts are common in fish and often impact trophically transmitted parasite communities. How parasite species composition and relative abundances change among size classes, and at what rate these changes occur, is rarely examined. Hosts with a broad trophic niche are potentially exposed to a large variety of parasite species. The degree of ontogenetic changes in parasite species composition versus changes in parasite abundance should suggestively differ between thropically generalist and specialist host species. In the present study, we explore ontogenetic dietary shifts and their impact on species composition and relative abundance of intestinal parasites in two sympatric salmonid fish species, Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) caught in the littoral habitat of a subarctic lake. Our results highlight a close interplay between ontogenetic dietary niche shifts and alterations in the acquisition of trophically transmitted parasites, leading to host-specific differences in the component community of parasites. Ontogenetic changes in the intestinal parasite community related to dietary niche shifts were distinct but less pronounced in Arctic charr than in brown trout due to a broader and more consistent dietary niche of the former and an ontogenetic shift toward piscivory in the latter. At the component community level, changes in parasite assemblages of both host species were driven by a faster increase in the heterogeneity of parasite relative abundance than in the compositional heterogeneity, a pattern that partly may be related to a rather species-poor parasite community of this subarctic study system. Separating compositional heterogeneity from heterogeneity in relative parasite abundance is important to understand how size-dependent variability shapes parasite communities of host populations.

Kelimpahan Populasi dan Tingkat Parasitisasi Parasitoid Indigenus terhadap Hama Invasif Liriomyza trifolii (Burgess) (Diptera: Agromyzidae) pada Tanaman Asteraceae di Bali

Population Abundance and Parasitization Level of Indigenous Parasites to Invasive Liriomyza trifolii (Burgess) (Diptera: Agromyzidae) on Asteraceae Plants in Bali. This study was aimed to determine the population abundance and parasitization level of indigenous parasitoid associated with Liriomyza trifolii (Burgess) in Asteraceae plants in Bali. The study was conducted from January to March 2019 by survey method on the type of parasitoid, abundance and parasitisation level in Asteraceae plants which included to Chrysanthemum, Gerbera jamesonii and Helianthus annuus, which are spread in several regencies in Bali such as Buleleng (1200 m asl), Bangli (900-1000 m asl) and Denpasar (40 m asl). Sampling was done purposively on the leaves of plants attacked by Liriomyza sp. and then maintained at the Laboratory until the parasitoid adults appeared. Afterward, morphologically was identified the type of parasitoid that appears. The results showed that there were three types of indigenous parasitoid associated with L. trifolii namely Hemiptarsenus varicornis, Neochrysocharis okazakii, and Opiusdissitus. The most dominant parasitoid of the three types of H. varicornis parasitoid with an abundance of 78.57% and parasitization rate of 53.23% was found in Chrysanthemum plants.

Effects of land use change (rural-urban) on the diversity and epizootiological parameters of avian Haemosporida in a widespread neotropical bird

Transformation of natural environments for livestock, agriculture and human settlements modifies the diversity of organisms, usually decreasing in highly disturbed land uses. Like their hosts, parasites have to adapt to novel human impacted landscapes, in which the abiotic and biotic conditions are radically different from those of conserved natural environments. We evaluated the diversity (alpha and beta taxonomic and phylogenetic diversity) of haemosporidians (mtDNA cyt b lineages) in the common chlorospingus (Chlorospingus flavopectus) at five land use types. We further analyzed the response of prevalence, parasitaemia and parasite aggregation to land use types and seasonality. Parasite lineage richness (i.e., haplotypes) and abundance (no. infected hosts) decreased with disturbance. Parasite assemblages were commonly dominated by either one of two lineages, one dominant in the urban greenspace (pBAEBIC02) and the other dominant in well-preserved mountain cloud forest (hCHLFLA01). Beta diversity was mainly explained by lineage turnover. Phylo beta diversity was low (i.e., lineages are closely related). Overall prevalence increased in wet season that coincides with host's breeding season. Haemoproteus and Plasmodium prevalence presented the opposite response to urbanization (negative and positive, respectively). Parasitaemia presented similar values across land uses for both genera and seasons, while Plasmodium aggregation decreased with urbanization. Thus, some parasite lineages (pBAEBIC02) will benefit from the urbanization process, while others will entirely disappear from cities (hCHLFLA01).

Explaining prevalence, diversity and host specificity in a community of avian haemosporidian parasites

Many hypotheses attempt to explain parasite–host associations, but rarely are they examined together in a single community. For hosts, key traits are the proportion of infected individuals (prevalence) and the diversity of parasites infecting them. A key parasite trait is host specificity, ranging from specialists infecting one or a few closely related species to generalists infecting many species. We tested 10 hypotheses to explain host‐parasite associations; five ‘host‐centric’ (e.g. prevalence is related to host abundance) and five ‘parasite‐centric’ (e.g. parasite abundance is related to host specificity). We analyzed a community of 67 locally transmitted avian haemosporidian parasite lineages (genera Plasmodium, Haemoproteus or Leucocytozoon), sampled from 2726 birds (64 species) in southern Sweden. Among host‐centric hypotheses, Haemoproteus and Leucocytozoon prevalence and Haemoproteus diversity were related to host habitat preferences, whereas there were no relationships with host abundance or body mass. Haemoproteus and Leucocytozoon prevalences were more similar among closely related than among distantly related host species. Haemoproteus prevalence and diversity were lower in host species with few close relatives (‘evolutionarily distinct’ hosts). Among parasite‐centric hypotheses, most lineages, even relative generalists, infected closely related host species more often than expected by chance. However, the host species of Haemoproteus and Leucocytozoon lineages overlapped less among lineages than expected by chance. Specialists did not reach higher prevalences than generalists on single host species. However, the abundance of Haemoproteus lineages was related to host specificity with generalists more common than specialists; this was driven by three closely related generalists. Host specificity of parasites was unrelated to the abundance or evolutionarily distinctiveness of their hosts. Parasite communities are likely structured by many factors and cannot be explained by hypotheses focusing solely on hosts or parasites. However, we found consistent effects of host phylogenetic relationships, plausibly a result of evolutionarily conserved host immune systems limiting parasite distributions.

Quantification of parasite abundance: A novel method to evaluate anti-Cryptocaryon irritans efficacy

Cryptocaryon irritans can cause mass mortality of cultured marine fish. There are few strategies that are efficacious for the control of the agent. As such, a robust assessment of alternative/novel chemotherapeutic agents against parasites within infected hosts is needed. This study aimed to establish a novel method by designing a particular device to determine parasite abundance for evaluating anti-C. irritans efficacy. A device was designed, which is primarily consists of an enclosure and a placemat. The device was used to determine the regular pattern of C. irritans shedding from infected Trachinotus ovatus. A positive correlation was observed between different inoculum doses and parasite abundance. The parasite sampling method was also used to evaluate the effect of amprolium hydrochloride dose (0, 0.5, 1.0, and 2.0 g/kg feed) against C. irritans infection. The results showed that the device collected >99.86% tomonts at 2–4 days of post-infection. Furthermore, a linear model was established to analyze infectious dose and parasite abundance (y = 192.5 + 3.961×). The coefficient of determination (R2) value was 0.990. The results of the amprolium hydrochloride treatment showed that the parasite abundance in the chemotherapeutic treatment groups were significantly reduced by 14.54%, 20.61%, and 37.10%, respectively, compared to the control group. The observed efficacy was dose-dependent, which indicated that the chemical protection against C. irritans infection could be successfully evaluated by this method. Here, a device was designed to accurately measure the number of tomonts, which can be useful in determining parasite abundance and assessing anti-C. irritans efficacy of chemotherapeutics.

Community structure and functional feeding groups of macroinvertebrates in pristine Andean streams under different vegetation cover

ABSTRACT As a function of the dominant vegetation cover, patterns of variation in the structure and composition of both, the aquatic macroinvertebrate communities and their functional feeding groups (FFG) were examined at pristine streams of two high Andean micro-catchments of southern Ecuador. Ten sampling segments were defined in the study streams surrounded by either Tussock grass (TG), Quinua forest (QF) or high mountain forest (HMF). In each segment, environmental and biological samples were collected. Different statistical analyses were implemented for assessing possible relationships between biological and environmental variables. TG and QF streams were found to share many physical and biological characteristics. HMF ecosystems, which are characterised by greater total hardness, water velocity, temperature, pH and nitrite/nitrate concentrations exhibited low values of diversity, richness, relative abundance of non-insects, piercer and parasites. Further, high values of relative abundance of Plecoptera (predators) were observed in HMF, apparently due to higher water velocities and their resistance to these flow conditions. The composition of the macroinvertebrate community showed similarity in TG and QF. It was observed at the three study sites a dominance of organisms generally tolerant to lower availability of oxygen (Chironomidae and non-insect class) and, curiously, to higher concentrations of nutrients. It was found some taxa associated with the presence of organic matter in the sediment because they use allochthonous resources (Phylloecus).

Soil Microbes Trade-Off Biogeochemical Cycling for Stress Tolerance Traits in Response to Year-Round Climate Change.

Winter air temperatures are rising faster than summer air temperatures in high-latitude forests, increasing the frequency of soil freeze/thaw events in winter. To determine how climate warming and soil freeze/thaw cycles affect soil microbial communities and the ecosystem processes they drive, we leveraged the Climate Change across Seasons Experiment (CCASE) at the Hubbard Brook Experimental Forest in the northeastern United States, where replicate field plots receive one of three climate treatments: warming (+5°C above ambient in the growing season), warming in the growing season + winter freeze/thaw cycles (+5°C above ambient +4 freeze/thaw cycles during winter), and no treatment. Soil samples were taken from plots at six time points throughout the growing season and subjected to amplicon (rDNA) and metagenome sequencing. We found that soil fungal and bacterial community composition were affected by changes in soil temperature, where the taxonomic composition of microbial communities shifted more with the combination of growing-season warming and increased frequency of soil freeze/thaw cycles in winter than with warming alone. Warming increased the relative abundance of brown rot fungi and plant pathogens but decreased that of arbuscular mycorrhizal fungi, all of which recovered under combined growing-season warming and soil freeze/thaw cycles in winter. The abundance of animal parasites increased significantly under combined warming and freeze/thaw cycles. We also found that warming and soil freeze/thaw cycles suppressed bacterial taxa with the genetic potential for carbon (i.e., cellulose) decomposition and soil nitrogen cycling, such as N fixation and the final steps of denitrification. These new soil communities had higher genetic capacity for stress tolerance and lower genetic capacity to grow or reproduce, relative to the communities exposed to warming in the growing season alone. Our observations suggest that initial suppression of biogeochemical cycling with year-round climate change may be linked to the emergence of taxa that trade-off growth for stress tolerance traits.

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.

Green patches among a grey patchwork: the importance of preserving natural habitats to harbour cavity-nesting bees and wasps (Hymenoptera) and their natural enemies in urban areas

Urbanisation is fast-growing worldwide characterised by the conversion of natural vegetation ecosystems into densely paved areas with a high concentration of human constructions and few remnants of natural habitats. This phenomenon may threaten wildlife, especially high trophic level organisms such as predators and parasitoids, which are known to be more sensitive to habitat fragmentation. We investigated the influence of urbanisation on the community of trap-nesting bees and wasps as well as on their parasites in an urban area. Trap-nests were installed in 11 areas within the perimeter of the city of Ribeirao Preto, Brazil. Fourteen land cover categories were distinguished and their percentages calculated for each area from satellite images. The community sampled consisted of 20 wasp and 12 bee species, as well as 25 natural enemy species that attacked 9.75% of the nests. The highest diversity of bees and wasps was observed in areas with higher percentages of natural vegetation, i.e., forests, wastelands, and neighbourhoods with extensive green areas. Rates of parasitism, measured by the abundance and richness of parasites, was positively correlated with the proportion of green areas in the landscape. Even though predatory wasps constitute a higher trophic level than bees they were not more negatively impacted by urbanisation. Our results demonstrate that natural habitats and extensive green areas can host diverse communities of cavity-nesting bees, wasps, and their parasites within a city. The conservation of green areas in urbanised landscapes should be considered as essential to maintain the populations of these important insects.

Meta-analysis of seasonal dynamics of parasite infections in aquatic ecosystems

Seasonal infection dynamics characterise many host-parasite interactions, as abiotic conditions drive fundamental biological processes in both hosts and parasites. The extent to which seasonal cycles in parasite abundance are universal, and whether the same underlying mechanisms are responsible for seasonality across different host-parasite associations, have received little attention to date. Here, global patterns of seasonal infection dynamics are tested using a meta-analysis of 693 seasonal contrasts in the local abundance of metazoan parasites in aquatic vertebrates, representing 343 parasite species and 148 host species. These include both contrasts between winter and summer in temperate systems, and between wet and dry seasons in tropical systems. Overall, the analysis found no evidence that seasonal infection dynamics are universal, nor that they are controlled by the same factors. More specifically, the results indicate no overall effect of the magnitude of local seasonal differences in abiotic conditions (temperature or precipitation), type of host (amphibian or fish), habitat (freshwater, coastal marine or deep-sea), host body length, or mode of transmission (skin contact or trophic) on the extent of seasonal differences in parasite infections. Instead, the results revealed many clear taxon-specific or habitat-specific patterns of seasonal infection dynamics, with some parasite or host taxa generally showing distinct peaks in infections in summer or dry seasons, and others showing no seasonal changes. The present findings serve to identify empirically which host-parasite associations are most likely to respond to changing climatic conditions, and thus provide useful information for fisheries and aquaculture.

Effects of the invasive common milkweed (Asclepias syriaca) on nematode communities in natural grasslands

Summary Thousands of plant species have been introduced, both deliberately and accidentally, to native ecosystems across the globe. The common milkweed, Asclepias syriaca, is an invasive fast-growing plant species that has invaded natural and managed areas in Europe in recent years. However, only a few studies have investigated its impacts on above-ground and below-ground native biota. Soil nematodes are considered to be the most abundant metazoans, comprising different trophic groups. We examined soil nematode populations on several independent sites invaded and non-invaded by A. syriaca in southern Slovak Republic. We hypothesised that alteration of above-ground nutrient sources caused by invasion would alter nematode abundance, species diversity and trophic structure. Our study revealed that the nematode communities were not negatively affected by A. syriaca invasion over a period of two vegetation seasons. The most surprising results were that common milkweed did not decrease the abundance of plant parasites, bacterivores or fungivores and did not affect species diversity. Moreover, basic physicochemical soil parameters were similar in both invaded and non-invaded sites, although there is evidence that invasive milkweed considerably decreases native plant species cover. It is thus reasonable to conclude that A. syriaca does not pose a threat to soil nematode communities but has a negative impact on native plants. As there is an absence of nematological studies from A. syriaca-invaded ecosystems and considering it has invaded a wide range of habitats, it is impossible to generalise our findings and further studies are required.

Immunity and health of two wild marine fishes naturally exposed to anthropogenic pollution

There are increasing global concerns of the alarming pollution impacts on marine life, thus it is becoming essential to generate reliable tools to monitor and understand the effects of these impacts on aquatic organisms. We performed a field study assessing how exposure to anthropogenic pollution impacts immunological and health-state parameters and parasite infection of a wild marine fish, the Brazilian sandperch Pinguipes brasilianus. Then we compared this information to previously published data of a sympatric species, the Patagonian rockfish Sebastes oculatus inhabiting the same polluted and pristine areas. The field study revealed that exposed P. brasilianus showed chronic stress, poor immune condition and higher prevalence and abundance of acanthocephalan parasites. By comparing these former results with already published in S. oculatus, we concluded that, although both species exhibited physiological alterations associate to inhabiting sites exposed to pollution, their specific immunological and health-state responses differed. Our results demonstrate that Patagonian reef-fish assemblages inhabiting sites exposed to pollutant are being affected in their immune and heath condition, which could potentially result in higher susceptibility to disease and in turn population decline. These findings highlight the necessity of more studies incorporating interspecific comparisons to assess variation in fish susceptibility in an ecoimmunotoxicological context and get a more profound understanding of anthropogenic impacts on wildlife.

The effect of parasite density on host colonisation success by a mobile avian ectoparasite

1. Full understanding of the dynamics of host–parasite interactions requires elucidation of the principles governing host colonisation. With respect to mobile parasites, little is known about their dispersal behaviour and the factors affecting host colonisation success.2. Here, the effect of parasite density manipulations on the colonisation success of the carnid fly Carnus hemapterus, an avian ectoparasite, was experimentally explored.3. Most host nests were colonised within the same breeding season, but the abundance of flies colonising the nests varied broadly both within and between years.4. Experimental increase in the density of carnid flies in the vicinity of host nests did not result in higher parasite abundance in these nests. Host colonisation success in terms of parasite abundance was not related to indices of parasite density around host nests.5. Parasite abundance in colonised host nests was positively related to host density and brood mass and negatively related to date. Host nests in trees held fewer carnid flies than those on cliffs and farmhouses.6. The dispersal ability of C. hemapterus is apt for rapid colonisation of new host nests, but it is unable to explain the broad heterogeneity in parasite abundance between host nests.

It's a wormy world: Meta-analysis reveals several decades of change in the global abundance of the parasitic nematodes Anisakis spp. and Pseudoterranova spp. in marine fishes and invertebrates.

The Anthropocene has brought substantial change to ocean ecosystems, but whether this age will bring more or less marine disease is unknown. In recent years, the accelerating tempo of epizootic and zoonotic disease events has made it seem as if disease is on the rise. Is this apparent increase in disease due to increased observation and sampling effort, or to an actual rise in the abundance of parasites and pathogens? We examined the literature to track long-term change in the abundance of two parasitic nematode genera with zoonotic potential: Anisakis spp. and Pseudoterranova spp. These anisakid nematodes cause the disease anisakidosis and are transmitted to humans in undercooked and raw marine seafood. A total of 123 papers published between 1967 and 2017 met our criteria for inclusion, from which we extracted 755 host-parasite-location-year combinations. Of these, 69.7% concerned Anisakis spp. and 30.3% focused on Pseudoterranova spp. Meta-regression revealed an increase in Anisakis spp. abundance (average number of worms/fish) over a 53 year period from 1962 to 2015 and no significant change in Pseudoterranova spp. abundance over a 37 year period from 1978 to 2015. Standardizing changes to the period of 1978-2015, so that results are comparable between genera, we detected a significant 283-fold increase in Anisakis spp. abundance and no change in the abundance of Pseudoterranova spp. This increase in Anisakis spp. abundance may have implications for human health, marine mammal health, and fisheries profitability.