Host-parasite Relationship Research Articles

Morphological and molecular identification of the hard ticks parasitizing Tremarctos ornatus (Carnivora: Ursidae) from paramo of Ecuador

The Andean bear or spectacled bear, Tremarctos ornatus (Cuvier), inhabits the Andes and is considered an endangered species due to anthropogenic factors. The aim of this study was to identify the tick species parasitizing the Andean bears in the evergreen shrubland and paramo grassland ecosystem in the Andes Mountain Range of Ecuador. Twenty-six ticks were removed from five Andean bears and morphologically identified as Amblyomma multipunctum Neumann, Ixodes boliviensis Neumann and Ixodes montoyanus Cooley. One specimen of each species was also molecularly analyzed and confirmed by BLAST. This study confirms the presence of I. boliviensis parasitizing T. ornatus and adds new records of A. multipunctum and I. montoyanus in its distribution. The parasite-host relationships are new in all cases for Ecuador.

Amoebiasis: Advances in Diagnosis, Treatment, Immunology Features and the Interaction with the Intestinal Ecosystem.

This review of human amoebiasis is based on the most current knowledge of pathogenesis, diagnosis, treatment, and Entamoeba/microbiota interactions. The most relevant findings during this last decade about the Entamoeba parasite and the disease are related to the possibility of culturing trophozoites of different isolates from infected individuals that allowed the characterization of the multiple pathogenic mechanisms of the parasite and the understanding of the host-parasite relationship in the human. Second, the considerable advances in molecular biology and genetics help us to analyze the genome of Entamoeba, their genetic diversity, and the association of specific genotypes with the different amoebic forms of human amoebiasis. Based on this knowledge, culture and/or molecular diagnostic strategies are now available to determine the Entamoeba species and genotype responsible for invasive intestinal or extraintestinal amoebiasis cases. Likewise, the extensive knowledge of the immune response in amoebiasis with the appearance of new technologies made it possible to design diagnostic tools now available worldwide. Finally, the understanding of the interaction between the Entamoeba species and the intestinal microbiota aids the understanding of the ecology of this parasite in the human environment. These relevant findings will be discussed in this review.

The unified theory of sleep: Eukaryotes endosymbiotic relationship with mitochondria and REM the push-back response for awakening

The Unified Theory suggests that sleep is a process that developed in eukaryotic animals from a relationship with an endosymbiotic bacterium. Over evolutionary time the bacterium evolved into the modern mitochondrion that continues to exert an effect on sleep patterns, e.g. the bacterium Wolbachia establishes an endosymbiotic relationship with Drosophila and many other species of insects and is able to change the host's behaviour by making it sleep. The hypothesis is supported by other host-parasite relationships, e.g., Trypanosoma brucei which causes day-time sleepiness and night-time insomnia in humans and cattle. For eukaryotes such as Monocercomonoids that don't contain mitochondria we find no evidence of them sleeping.Mitochondria produce the neurotransmitter gamma aminobutyric acid (GABA), and ornithine a precursor of the neurotransmitter GABA, together with substances such as 3,4dihydroxy phenylalanine (DOPA) a precursor for the neurotransmitter dopamine: These substances have been shown to affect the sleep/wake cycles in animals such as Drosophilia and Hydra.Eukaryote animals have traded the very positive side of having mitochondria providing aerobic respiration for them with the negative side of having to sleep. NREM (Quiet sleep) is the process endosymbionts have imposed upon their host eukaryotes and REM (Active sleep) is the push-back adaptation of eukaryotes with brains, returning to wakefulness.

Haemoproteus parasites and passerines: the effect of local generalists on inferences of host-parasite co-phylogeny in the British Isles.

Host–parasite associations provide a benchmark for investigating evolutionary arms races and antagonistic coevolution. However, potential ecological mechanisms underlying such associations are difficult to unravel. In particular, local adaptations of hosts and/or parasites may hamper reliable inferences of host–parasite relationships and the specialist–generalist definitions of parasite lineages, making it problematic to understand such relationships on a global scale. Phylogenetic methods were used to investigate co-phylogenetic patterns between vector-borne parasites of the genus Haemoproteus and their passeriform hosts, to infer the ecological interactions of parasites and hosts that may have driven the evolution of both groups in a local geographic domain. As several Haemoproteus lineages were only detected once, and given the occurrence of a single extreme generalist, the effect of removing individual lineages on the co-phylogeny pattern was tested. When all lineages were included, and when all singly detected lineages were removed, there was no convincing evidence for host–parasite co-phylogeny. However, when only the generalist lineage was removed, strong support for co-phylogeny was indicated, and ecological interactions could be successfully inferred. This study exemplifies the importance of identifying locally abundant lineages when sampling host–parasite systems, to provide reliable insights into the precise mechanisms underlying host–parasite interactions.

Elemental content of a host-parasite relationship in the threespine stickleback.

Parasite infections are ubiquitous and their effects on hosts could play a role in ecosystem processes. Ecological stoichiometry provides a framework to study linkages between consumers and their resource, such as parasites and their host, and ecosystem process; however, the stoichiometric traits of host-parasite associations are rarely quantified. Specifically, it is unclear whether parasites' elemental ratios closely resemble those of their host or if infection is related to host stoichiometry, especially in vertebrate hosts. To answer such questions, we measured the elemental content (%C, %N, and %P) and molar ratios (C:N, C:P, and N:P) of parasitized and unparasitized Gasterosteus aculeatus (three-spined stickleback) and their cestode parasite, Schistocephalus solidus. Host and parasite elemental content were distinct from each other, and parasites were generally higher in %C and lower in %N and %P. Parasite infections were related to host C:N, with infected hosts being lower in C:N. Parasite elemental content was independent of their host, but parasite body mass and parasite density were important drivers of parasite stoichiometry. Overall, these potential effects of parasite infections on host stoichiometry along with parasites' distinct elemental compositions suggest parasites may further contribute to differences in how individual hosts store and recycle nutrients.

Эколого-биологические и морфологические особенности возбудителя трихинеллёза в Кировской области и оптимизация мер борьбы

Trichinellosis is one of the most dangerous zoonosis. The analysis of different methods of prevention in helminthology indicates an increasing attention to such zoonotic diseases as trichinellosis in the World and Russia. Wild animals as a source of infection play the leading role in human infection. The task of present work is diagnostics, prevention of helminthozoonosis and improved monitoring and surveillance of the dissemination of trichinellosis. Practical application of expertise of meat and meat products from hunter’s trophies allows preventing infection of human and domestic animals with dangerous zoonosis. The article considers the influence of low temperatures, and the improvement of the fight against trichinosis in the northern territories. The index and shape of the capsule of trichinella in carnivores have differences. Apparently, these features are due to the peculiarities of parasite-host relationships and differences in the morphology of muscle tissue myosymplasts in various animals, and are species-specific for the host animals of trichinella. The conducted studies confirm the effectiveness of the combination of methods of compressor trichinoscopy and digestion in the artificial gastric juice for postmortem diagnosis of trichinosis of wild animals. When comparing these methods, it was found that the method of digestion in artificial gastric juice is more sensitive compared to compressor trichinoscopy, but it is less effective in detecting dead trichinella. New technologies for disinfection of carcasses and residual muscle mass after hides have been milled have also been developed for mechanical harvesting stations; for this, special refrigerating chambers and solutions of disinfectants have been proposed. Trichinella of the northern territories are more resistant to low temperatures, therefore, disinfection modes should be increased (both temperature and exposure time). So, for example, if pork is frozen at a temperature of -15 oC, and according to the recommendation of the International Commission on Trichinosis, it is necessary to keep the meat for at least 3–4 weeks, and carcasses of wild animals should be frozen for at least 3 weeks at a temperature of less than -20 oC.

Anthelmintic Treatment and the Stability of Parasite Distribution in Ruminants.

Parasites are generally overdispersed among their hosts, with far-reaching implications for their population dynamics and control. The factors determining parasite overdispersion have long been debated. In particular, stochastic parasite acquisition and individual host variation in density-dependent regulation through acquired host immunity have been identified as key factors, but their relative roles and possible interactions have seen little empirical exploration in parasite populations. Here, Taylor's power law is applied to test the hypothesis that periodic parasite removal destabilises the host-parasite relationship and increases variance in parasite burden around the mean. The slope of the power relationship was compared by analysis of covariance among 325 nematode populations in wild and domestic ruminants, exploiting that domestic ruminants are often routinely treated against parasite infections. In Haemonchus spp. and Trichostrongylus axei in domestic livestock, the slope increased with the frequency of anthelmintic treatment, supporting this hypothesis. In Nematodirus spp., against which acquired immunity is known to be strong, the slope was significantly greater in post-mortem worm burden data than in faecal egg counts, while this relationship did not hold for the less immunogenic genus Marshallagia. Considered together, these findings suggest that immunity acting through an exposure-dependent reduction in parasite fecundity stabilises variance in faecal egg counts, reducing overdispersion, and that periodic anthelmintic treatment interferes with this process and increases overdispersion. The results have implications for the diagnosis and control of parasitic infections in domestic animals, which are complicated by overdispersion, and for our understanding of parasite distribution in free-living wildlife. Parasite-host systems, in which treatment and immunity effectively mimic metapopulation processes of patch extinction and density dependence, could also yield general insights into the spatio-temporal stability of animal distributions.

Science school in ecological parasitology in Karelia

The ecological concept of parasitism as a general biology phenomenon underlies the understanding of the role of parasites in terrestrial and aquatic ecosystems. The review gives an account of the current positioning of parasitology in the system of biological sciences, the subject and tasks of ecological parasitology. We relate the history of the science school in parasitology at the Institute of Biology KarRC RAS, which took shape under the leadership of pupils of the founder of the Russian school in ecological parasitology, outstanding scholar from Leningrad V. A. Dogiel. Major stages and areas of research and methodological approaches to the study of parasites and host-parasite relationships are described, covering a wide range of objects: blood-sucking arthropods, parasites of fish, birds, mammals, and plants. Studies deal with the formation and dynamics of parasitic communities in natural and disturbed terrestrial and aquatic ecosystems (eutrophication, industrial pollution, alien species invasions, aquaculture). The results of these studies are of high theoretical significance and have been published in monographs and in articles in Russian and international journals. Practical recommendations are widely applied in nature management, veterinary and agricultural practices, and are annually published in the Republic of Karelia State Report on the Environment. Today, the science school in ecological parasitology in Karelia is represented by qualified specialists, who investigate a wide range of both basic and applied topics, including those of special relevance for the region.

A subterranean new genus and species of Eutrombidiinae (Trombidiformes: Microtrombidiidae) from Turkey

A new genus and species of the Microtrombidiidae, Troglotrombidium dolichopodum n. gen. et n. sp. is described based on ectoparasitic larvae collected from two Dolichopoda lycia (Galvagni 2006) (Orthoptera: Rhaphidophoridae) specimens from a cave in Western Taurus Mountains, Turkey. The new genus can be distinguished from other genera by the absence of eyes, highly modified claws of tarsi III, sensillary setae structure of the anterior dorsal scutum, and the number of adoral setae. The new species is a typical troglobite, and this interspecific interaction is a well-documented case for the little-known host-parasite relationships from subterranean ecosystems.

PECULIARITIES OF ECOLOGY AND AEROBONE RESPIRING OF NEMATODES OF THE SPECIES DICTYOCAULUS FILARIA PARASITES OF RUMINANTS

Summary Nematodes of the species Dictyocaulus filaria parasitize in the lungs of ungulates, negatively affect the host organism, affecting the metabolism. The cycle of development of the considered nematodes occurs in a direct way, i.e. without the intervention of an intermediate host. The contact of invasive elements with the final host occurs through trophic channels within the "parasite-host" system. The age composition of the population of the genus Dictyocaulus consists of free-living and parasitic groups. Each group occupies a certain ecological niche in biocenoses. A high aerobic respiration of the nematode D. filaria was established in comparison with warm-blooded rats. The inhibitory analysis of nematode respiration allows us to note that the respiratory system of these organisms is largely focused on the consumption of amino acids and their dicarboxylic products. This circumstance is important for assessing the metabolic factor in the host-parasite relationship and the nature of the parasitism of the studied nematodes, one of the consequences of which may be the depletion of vital proteins and amino acids, as well as a decrease in the access of oxygen to the host organism.

Molecular investigation on infection by haemosporidians in three Western Palearctic species of swift (Apodidae) and their ectoparasitic louse flies.

Swifts (Apodidae) are an unusual group of birds that spend most of their lives in flight, landing only when breeding. Although this aerial lifestyle greatly reduces their likelihood of being bitten by vectors and infected by vector-born parasites, swifts can still be heavily infested during breeding by nest-based vectors such as louse flies (Hippoboscidae). Here, we investigated host, vector, and vector-borne parasite relationships in the three most widespread swift species in the Western Palearctic (WP): common swifts (Apus apus), pallid swifts (A. pallidus), and alpine swifts (Tachymarptis melba), their nest-based louse flies (Crataerina pallida and C. melbae) and avian haemosporidians (genera Haemoproteus, Plasmodium, and Leucocytozoon). Studies of haemosporidian infections in Apodidae remain limited, with clear evidence of infection found to date in just four Neotropical and one Australasian species. The possible role of louse flies in transmitting haemosporidian infections has never been tested in swifts. We assessed the occurrence of haemosporidian infection by PCR screenings of DNA from blood samples from 34 common swifts and 44 pallid swifts from Italy, and 45 alpine swifts from Switzerland. We also screened 20 ectoparasitic louse flies present on 20 birds and identified them by both morphological features and cytochrome oxidase subunit 1 (COI) barcodes. Our results provide no evidence of haemosporidian infection in the 123 swifts tested or in the two louse fly species we identified. Our findings are consistent with available knowledge showing no haemosporidian occurrence in WP swift species and that the most likely infection route for these highly aerial species (via louse fly ectoparasites during nesting) is unlikely.

Do natural catastrophic events and exceptional climatic conditions also affect parasites?

Parasites and parasitologists have always lived together in good and bad luck in a sort of forced marriage. In recent times bad luck certainly prevailed, because of increasing man-made emergencies such as wars, chemical disasters, but also because of natural disasters, amplified by climate change, that condition more and more parasite–host equilibrium. The symposium at the National Congress of the Italian Society for Parasitology, was a first occasion for Italian parasitologists to reason about ‘disaster parasitology’ and researchers’ responsibilities. Extreme weather events and their impacts on parasites’ epidemiology are illustrated, comparing disasters that recently occurred in Italy with literature data. In particular, the Sardinian Island was hit subsequently by fires and floods exacerbating the effects on ecosystems and parasite–host-relationships. Examples of Cryptosporidium outbreaks in man and Fasciola hepatica infections in various hosts after heavy rains are reviewed and effects of droughts on pasture borne parasites, such as gastro-intestinal nematodes of ruminants are discussed. Heavy rains may also cause dissemination of toxic substances released accidentally from chemical plants as happened e.g. in Milan province (IT) after the dioxin hazard. The overlapping effects of strictly man-made disasters with climate change dependent extreme weather events is further challenging the understanding of what are the consequences of disasters on ecosystems and parasite epidemiology.GIS applications combined with AI programs may help to face the complex challenges, allowing the collection and analysis of spatial/temporal data at whatever level desired. Examples illustrated in the article suggest their employment also in a more systematic, prevention-oriented manner.

Three New Species of Jainus (Monogenea: Dactylogyridae) Parasitizing Gills of Brazilian Freshwater Fishes Supported by Morphological and Molecular Data

The present study describes three new species of monogeneans parasitizing the gills of anostomid fishes from the Upper Paraná River basin, southeastern Brazil: Jainus beccus n. sp. and Jainus radixelongatus n. sp. on Leporinus friderici, Leporinus octofasciatus, Leporinus striatus, and Megaleporinus elongatus; and Jainus ornatus n. sp. on L. friderici. The new species differ from other congeners by the morphology of the accessory piece. There is a semicircular distal portion resembling a “bird’s beak” in Jainus beccus n. sp. It composed of two subunits—one ventral and more sclerotized, sickle-shaped, and another dorsal with three projections—in Jainus radixelongatus n. sp. There are two elongated and sclerotized subunits, both of which have a sickle-shaped distal portion, in Jainus ornatus n. sp. Supplementary observations not reported in the original descriptions of the type-species Jainus piava Karling, Bellay, Takemoto & Pavanelli, 2011 are proposed, as follows: the presence of a thin and delicate ventral bar, which can vary greatly in shape; an accessory piece not articulated with the MCO’s base. This paper provides the first phylogenetic study based on LSU rDNA and COI mtDNA gene sequences for Jainus, improving and clarifying the understanding of host–parasite relationships in neotropical characiforms.

Anatomical, phenological and genetic aspects of the host-parasite relationship between Andrena vaga (Hymenoptera) and Stylops ater (Strepsiptera).

Stylops ater is an endoparasite of the mining bee Andrena vaga with extreme sexual dimorphism and hypermetamorphosis. Its population structure, parasitization mode, genetic diversity and impact on host morphology were examined in nesting sites in Germany to better understand this highly specialized host–parasite interaction. The shift in host emergence due to stylopization was proven to be especially strong in A. vaga. Around 10% of bees hosted more than 1 Stylops, with at maximum 4. A trend in Stylops' preference for hosts of their own sex and a sex-specific position of extrusion from the host abdomen was found. Invasion of Andrena eggs by Stylops primary larvae was depicted for the first time. Cephalothoraces of female Stylops were smaller in male and pluristylopized hosts, likely due to lower nutrient supply. The genes H3, 18S and cytochrome c oxidase subunit 1 were highly conserved, revealing near-absence of local variation within Stylops. Ovaries of hosts with male Stylops contained poorly developed eggs while those of hosts with female Stylops were devoid of visible eggs, which might be due to a higher protein demand of female Stylops. Male Stylops, which might have a more energy-consuming development, led to a reduction in head width of their hosts. Host masculinization was present in the leaner shape of the metabasitarsus of stylopized females and is interpreted as a by-product of manipulation of the host's endocrine system to shift its emergence. Stylopization intensified tergal hairiness, most strongly in hosts with female Stylops, near the point of parasite extrusion, hinting towards substance-induced host manipulation.

Context-dependent insect predation pressure on an avian ectoparasite.

Context dependence arises when ecological relationships vary with the conditions under which they are observed. Context dependence of interactions involving parasites is poorly known, even if it is key to understanding host-parasite relationships and food web dynamics. This paper investigates to which extent predation pressure on an avian ectoparasite (Carnus hemapterus) is context-dependent. Based on a predator-exclusion experiment, predation pressure on C. hemapterus pupae in the host's nest for 3 years, and its variation between habitat types are quantified. Variation in precipitation and normalized difference vegetation index (NDVI) is also explored as a likely cause of context dependency. We hypothesize that predation pressure should fluctuate with such surrogates of food availability, so that inter-annual and intra-annual differences may emerge. The number of nests with significant reduction of pupae varied widely among years ranging from 24% to 75%. However, average pupae reduction in nests where a significant reduction occurred did not vary between years. No differences in predation rates between habitat types were detected. Precipitation and NDVI varied widely between years and NDVI was consistently lower around nests on cliffs than around nests on trees and farmhouses. Parallels were found between variation in predation pressure and precipitation/NDVI at a wide scale (highest predation the driest year, and much lower the 2 rainier ones), but not at the nest scale. This paper shows clear context-dependent insect predation pressure on an ectoparasite under natural conditions, and that such interaction changes in signs rather than magnitude between years. The causes for these variations require longer-term studies and/or well-designed, large-scale experiments.

Fasciola hepatica juveniles interact with the host fibrinolytic system as a potential early-stage invasion mechanism.

The trematode Fasciola hepatica is the most widespread causative agent of fasciolosis, a parasitic disease that mainly affects humans and ruminants worldwide. During F. hepatica infection, newly excysted juveniles (FhNEJ) emerge in the duodenum of the mammalian host and migrate towards their definitive location, the intra-hepatic biliary ducts. Understanding how F. hepatica traverses the intestinal wall and migrates towards the liver is pivotal for the development of more successful strategies against fasciolosis. The central enzyme of the mammalian fibrinolytic system is plasmin, a serine protease whose functions are exploited by a number of parasite species owing to its broad spectrum of substrates, including components of tissue extracellular matrices. The aim of the present work is to understand whether FhNEJ co-opt the functions of their host fibrinolytic system as a mechanism to facilitate trans-intestinal migration. A tegument-enriched antigenic extract of FhNEJ (FhNEJ-Teg) was obtained in vitro, and its capability to bind the zymogen plasminogen (PLG) and enhance its conversion to the active protease, plasmin, were analyzed by a combination of enzyme-linked immunosorbent, chromogenic and immunofluorescence assays. Additionally, PLG-binding proteins in FhNEJ-Teg were identified by bidimensional electrophoresis coupled to mass spectrometry analysis, and the interactions were validated using FhNEJ recombinant proteins. Our results show that FhNEJ-Teg contains proteins that bind PLG and stimulate its activation to plasmin, which could facilitate the traversal of the intestinal wall by FhNEJ and contribute to the successful establishment of the parasite within its mammalian host. Altogether, our findings contribute to a better understanding of host-parasite relationships during early fasciolosis and may be exploited from a pharmacological and/or immunological perspective for the development of treatment and control strategies against this global disease.

Phylogenetic and host-parasite relationship analyses of Henneguya caquetaia sp. nov (Myxosporea: Myxobolidae) infecting an Amazonian cichlid fish

The present study describes a new species of Henneguya infecting the ornamental fish Caquetaia spectabilis from the Brazilian Amazon. Fish specimens were collected where the Tapajós and Amazon rivers merge, municipality of Santarém in the State of Pará, Brazil. Infections were intense, with several plasmodia spread on the opercula, fins and eye. Phylogenetic characterization and host-parasite relationship studies of the new Henneguya species used a combination of small subunit ribosomal DNA (ssrDNA) and morphological (photonic and transmission electron microscopy) analyses. Plasmodia were white round to ellipsoidal measuring up to 1.8 mm. The myxospores body measured 20.5 ± 3.9 (15–27) in length, 7.9 μm (6.2–10.8) in width, 6.7 μm (6.0–7.6) in thickness, 20.5 μm (14.4–32.3) in caudal appendages length, and 40.6 μm (34.2–54.6) in total length. The two polar capsules were elongated and equal in size, measuring 4.3 μm (3.3–5.4) in length and 2.1 μm (1.3–2.8) in width. Histological analysis revealed the parasite development in connective tissues of the fins, eyes and opercula. The skin of the fins and opercula presented detachment of the epidermis, however, no inflamatory infiltrate was observed. In the eye were observed inflammatory infiltratate in the epithelium and stroma of the cornea. Ultrastructure analysis showed the connective tissue capsule composed by an inner cellular layer with fibroblasts and outer layer where collagen fibers arranged transversely yet interspersed by layers of fibers arranged longitudinally. Numerous invaginations and extensive pinocytotic channels were observed in the plasmodial membrane. A layer of microfilament-like microfilament-like material was observed in the ectoplasm area and along to the internal surface of the plasmodial membrane. Generative cells and early stages of sporogenesis were seen more internally. The ssrDNA based phylogeny showed the South American species grouped in two lineages and the new species arises in a well-sustained subclade as sister branch of the clade composed by Henneguya spp. parasites of cichlids fish.

Unique Host-Parasite Relationships from Wildlife and Pets at a Zoological Medicine Service at Central Oklahoma

Ectoparasites on wild birds and mammals threaten health of the animal and community. Most studies of ectoparasites tend to be location focused so characterizing wider differences between ectoparasites and hosts is difficult. The aim of this study was to identify ectoparasites from free ranging and captive wildlife at an academic zoological medicine service in Central Oklahoma and record first reports of ectoparasites and hosts. We collected 228 ectoparasites from 47 animals: 111 ectoparasites from 30 birds were 14 lice (n = 78), four hematophagous fly (n = 20), and three tick (n = 13) species. One hundred seventeen ectoparasites from 17 mammals were four flea (n = 8) and four tick (n = 109) species. Results included 13 first-time ectoparasite species and 26 first-time host-ectoparasite reports in Oklahoma. The study portrays closer representation of ectoparasites infesting wild animals in Central Oklahoma and demonstrate possible correlation between mortality and injury to parasitized hosts. Additional studies would document ectoparasites infesting wildlife in Central Oklahoma.

Elevated nest temperature has opposing effects on host species infested with parasitic nest flies

Environmental factors, such as elevated temperature, can have varying effects on hosts and their parasites, which can have consequences for the net outcome of this relationship. The individual direct effects of temperature must be disentangled to determine the net-effect in host-parasite relationships, yet few studies have determined the net-effects in a multi-host system. To address this gap, we experimentally manipulated temperature and parasite presence in the nests of two host species infested by parasitic blowflies (Protocalliphora sialia). We conducted a factorial experiment by increasing temperature (or not) and removing all parasites (or not) in the nests of eastern bluebirds (Sialia sialis) and tree swallows (Tachycineta bicolor). We then measured nestling morphometrics, blood loss, and survival and quantified parasite abundance. We predicted that if temperature had a direct effect on parasite abundance, then elevated temperature would cause similar directional effects on parasite abundance across host species. If temperature had a direct effect on hosts, and therefore an indirect effect on the parasite, parasite abundance would differ across host species. Swallow nests with elevated temperature had fewer parasites compared to nests without temperature manipulation. In contrast, bluebird nests with elevated temperatures had more parasites compared to nests without temperature manipulation. The results of our study demonstrate that elevated temperature can have differential effects on host species, which can impact infestation susceptibility. Furthermore, changing climates could have complex net-effects on parasite fitness and host health across multi-host-parasite interactions.

Interactions between native and invasive species: A systematic review of the red squirrel-gray squirrel paradigm

The eastern gray squirrel (Sciurus carolinensis) has been labeled as one of the 100 worst invasive alien species by the IUCN. In Europe, the species has been introduced to Britain, Ireland and Italy, and its subsequent spread has resulted in wide-scale extinction of native Eurasian red squirrels (Sciurus vulgaris) from the areas colonized by the gray squirrel. This replacement of a native by an alien competitor is one of the best documented cases of the devastating effects of biological invasions on native fauna. To understand how this replacement occurs, we present a systematic review of the literature on competition and interactions between red and gray squirrels. We describe the patterns of red and gray squirrel distribution in those parts of Europe where gray squirrels occur and summarize the evidence on the different processes and mechanisms determining the outcome of competition between the native and alien species including the influence of predators and pathogens. Some of the drivers behind the demise of the red squirrel have been intensively studied and documented in the past 30 years, but recent field studies and mathematical models revealed that the mechanisms underlying the red-gray paradigm are more complex than previously thought and affected by landscape-level processes. Therefore, we consider habitat type and multi-species interactions, including host-parasite and predator-prey relationships, to determine the outcome of the interaction between the two species and to better address gray squirrel control efforts.