Individual hosts are often co-infected with multiple parasite species. Evidence from theoretical and empirical studies supports the idea that co-occurring parasites can impact each other and their ...hosts via synergistic or antagonistic interactions. The fundamental aim of understanding the consequences of co-infection to hosts and parasites requires an understanding of patterns of species co-occurrence within samples of hosts. We censused parasite assemblages in 755 adult, male fathead minnows collected from 7 lakes/ponds in southern Alberta, Canada between 2018 and 2020. Fifteen species of endoparasites infected fathead minnows, 98% of which were co-infected with between 2 and 9 parasite species (mean species richness: 4.4 ± 1.4). Non-random pairwise associations were detected within the overall parasite community. There were particularly strong, positive associations in the occurrences and intensities of the 2 congeneric larval trematodes Ornithodiplostomum sp. and Ornithodiplostomum ptychocheilus that comprised >96% of the 100 000+ parasites counted in the total sample of minnows. Furthermore, the occurrence of Ornithodiplostomum sp. was a strong predictor of the occurrence of O. ptychocheilus, and vice versa. Positive covariation in the intensities of these 2 dominants likely arises from their shared use of physid snails as first intermediate hosts in these waterbodies. These 2 species represent a predictable and non-random component within the complex assemblage of parasites of fathead minnows in this region.
The biodiversity and distributions of terrestrial snails at local and regional scales are influenced by their low vagility and microhabitat specificity. The accessibility of large-bodied species and ...their characteristically high levels of genetic polymorphism make them excellent ecological and evolutionary models for studies on the phylogeography, phylogenetics, and conservation of organisms in fragmented populations. This study aims to elucidate the biodiversity, systematics, and distributions of genetic lineages within the genus Oreohelix at the northern and western periphery of their range.
We found four mitochondrial clades, three of which are putative subspecies of Oreohelix subrudis. One clade was geographically widespread, occurring within numerous sites in Cypress Hills and in the Rocky Mountains, a second was geographically restricted to the Rocky Mountains in Alberta, and a third was restricted to the Cypress Hills region. A fourth clade was the small-bodied species, O. cooperi. ITS2 sequence and screening data revealed three genetic clusters, of which one was O. cooperi. Cluster 1 contained most individuals in COI clade X and some from clade B and cluster 2 was predominantly made up of individuals from COI clades B and B' and a few from clade X. ITS2 alleles were shared in a narrow contact zone between two COI clades, suggestive of hybridization between the two.
A sky island known as Cypress Hills, in southeastern Alberta, Canada, is a biodiversity hotspot for terrestrial land snails in the genus Oreohelix. The observed phylogeographic patterns likely reflect reproductive isolation during the Last Glacial Maximum, followed by secondary contact due to passive, long-range dispersal resulting from low vagility, local adaptation, and complex glacial history.
The dilution effect describes the negative association between host biodiversity and the risk of infectious disease. Tests designed to understand the relative roles of host species richness, host ...species identity, and rates of exposure within experimental host communities would help resolve ongoing contention regarding the importance and generality of dilution effects. We exposed fathead minnows to infective larvae of the trematode, Ornithodiplostomum ptychocheilus in minnow‐only containers and in mixed containers that held 1–3 other species of fish. Parasite infection was estimated as the number of encysted worms (i.e., brainworms) present in minnows following exposure. The results of exposure trials showed that nonminnow fish species were incompatible with O. ptychocheilus larvae. There was no reduction in mean brainworm counts in minnows in mixed containers with brook sticklebacks or longnose dace. In contrast, brainworm counts in minnows declined by 51% and 27% in mesocosms and aquaria, respectively, when they co‐occurred with emerald shiners. Dilution within minnow + shiner containers may arise from shiner‐induced alterations in minnow or parasite behaviors that reduced encounter rates between minnows and parasite larvae. Alternatively, shiners may act as parasite sinks for parasite larvae. These results highlight the role of host species identity in the dilution effect. Our results also emphasize the complex and idiosyncratic effects of host community composition on rates of parasite infection within contemporary host communities that contain combinations of introduced and native species.
The effects of host diversity on rates of parasite infection are context‐dependent. When fathead minnows swim in containers with one non‐host competitor (longnose dace), rates of infection into minnows are the same as when minnows swim in containers by themselves. In contrast, when minnows swim in containers with another species of non‐host competitor (emerald shiners), infection rates decrease by more than 50%.
The control of emerging parasites requires a fundamental knowledge of where and when rates of transmission are high. Data on spatiotemporal patterns of infection are challenging to obtain, ...particularly for complex life cycle parasites that involve transmission into multiple obligate hosts. The lancet liver fluke, Dicrocoelium dendriticum, has a long history of colonization outside its native host and geographical range in continental Europe. Infection patterns involving adult and metacercarial stages have been characterized for this trematode in a region of emergence in western Canada within co-grazing herbivores and ants, but infection patterns in snail intermediate hosts in this region are unknown. We combined spatiotemporal prevalence surveys with sequence analyses of the cytochrome c oxidase subunit 1 (COI) barcoding gene from samples of sporocyst tissue in infected snails to confirm that D. dendriticum utilizes 3 sympatric species of Oreohelid land snail (Oreohelix subrudis, Oreohelix sp., and Oreohelix cooperi) as first intermediate host. Mean prevalence within a total sample of 900 adult snails collected over 1 field season from 6 sites was 9.9 ± 2.4%. For each species of snail, prevalence ranged between 5–30% within monthly samples, with peaks in midsummer followed by declines in fall. Between-site variation in prevalence was low and nonsignificant, implying that rates of transmission of D. dendriticum miracidia from domestic stock and wildlife into snails are similar within localized sites, despite high variation in local habitat characteristics and in the structure of the definitive host community.
Morphological, gene sequence, host tissue tropism, and life cycle characteristics were utilized to describe the myxozoan, Myxobolus rasmusseni n. sp. from fathead minnow, Pimephales promelas, ...collected from reservoirs in southern Alberta. Results from serial histological sections of whole heads showed that myxospores were contained within irregular-shaped and sized coelozoic capsules (=plasmodia). Clusters of membrane-bound, myxospore-filled plasmodia filled the head cavities of juvenile fathead minnows, leading to the development of large, white, disfiguring lesions in mid to late summer. Bilateral exopthalmia (pop-eye disease) was a common outcome of M. rasmusseni n. sp. development. BLASTn search of a 1974 bp sequence of the 18S rDNA gene isolated from myxospores indicated that M. rasmusseni n. sp. was distinct from other coelozoic and histozoic Myxobolus spp. cataloged in GenBank. 18S rDNA gene sequences from triactinomyxon spores released from the oligochaete Tubifex were 100% identical to sequences from myxospores collected from syntopic fathead minnows. Results from a longitudinal survey of the 2020 cohort of fathead minnows showed that young-of-the-year are exposed at 1–5 mo and that 60–90% of these had developed myxospore-filled lesions approximately one year later. Data regarding potential sources and timing of M. rasmusseni n. sp. emergence in fathead minnow populations are needed.
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•a new species of coloezoic myxozoan is described from fathead minnow in southern Alberta, Canada.•Myxobolus rasmusseni n. sp. is closely related to Myxobolus spp. in other cyprinid fishes.•Myxospores reside within membrane-bound plasmodia that fill the head cavity of infected fish.•Exophthalmia (eye-bulge) is a common outcome of M. rasmusseni n. sp. development in fatheads.•M. rasmusseni n. sp. may be an emerging disease within populations of fatheads in this region.
Some patients have features that indicate possible difficulty with direct laryngoscopy for tracheal intubation. Prediction of the likely outcome and selection of patients for an enhanced management ...algorithm would reduce the possible harm from failed intubation attempts.
Adult elective patients were assessed for seven features associated with difficult direct laryngoscopy, ranked in difficulty from 0 to 3. For a patient with at least one Class 3 feature, or two or more features of class 1 or higher, the enhanced management used a channelled videolaryngoscope Airtraq™ instead of a Macintosh laryngoscope. A long flexible angulated stylet and a flexible fibrescope would be used as the second and third steps. For patients with lesser difficulty scores, a Macintosh laryngoscope was used. Outcomes of enhanced management were analysed. Logistic regression and Random Forest algorithm, using the ranks of the predictive features, were used to predict difficulty during enhanced management.
We prospectively studied 16 695 patients. We selected 1501 (9%) for enhanced management, and tracheal intubation was successful in all of them. Of these, 73% were intubated in less than 30 s, and only 4.5% required more than 4 min for intubation. Progression to the second and third steps of enhanced management was predicted by restriction of mouth opening and reduced cervical spine mobility.
An enhanced management algorithm allowed successful tracheal intubation of all patients with anticipated difficult laryngoscopy. The need to combine the use of a stylet and a fibrescope with the Airtraq™ could be predicted with a high degree of certainty.
Many fishes possess specialized epidermal cells that are ruptured by the teeth of predators, thus reliably indicating the presence of an actively foraging predator. Understanding the evolution of ...these cells has intrigued evolutionary ecologists because the release of these alarm chemicals is not voluntary. Here, we show that predation pressure does not influence alarm cell production in fishes. Alarm cell production is stimulated by exposure to skin-penetrating pathogens (water moulds: Saprolegnia ferax and Saprolegnia parasitica), skin-penetrating parasites (larval trematodes: Teleorchis sp. and Uvulifer sp.) and correlated with exposure to UV radiation. Suppression of the immune system with environmentally relevant levels of Cd inhibits alarm cell production of fishes challenged with Saprolegnia. These data are the first evidence that alarm substance cells have an immune function against ubiquitous environmental challenges to epidermal integrity. Our results indicate that these specialized cells arose and are maintained by natural selection owing to selfish benefits unrelated to predator-prey interactions. Cell contents released when these cells are damaged in predator attacks have secondarily acquired an ecological role as alarm cues because selection favours receivers to detect and respond adaptively to public information about predation.
I examined growth and survival of the European toad, Bufo bufo, from hatching to the approximate time of first hibernation. I varied tadpole density in experimental ponds such that individuals from ...low—density ponds emerged 48.5% larger than those from high—density ponds. In the laboratory, metamorphs from both pond densities were maintained in containers at densities of one or six. Nine weeks after metamorphosis they were exposed to 0 or 80 larvae of the lungworm, Rhabdias bufonis. A factorial experiment aimed to determine (1) the extent to which conditions experienced by larvae carried over to the terrestrial stage (2) the effects of resource limitation and past history on a host's response to a potential pathogen. The density of metamorphs had the strongest effect on growth and survival: 18 wk after metamorphosis, those raised alone were °80% heavier than those in groups and they had 31% higher survival. However, larval history also affected growth and survival and affected how metamorphs responded to density. First, single toads emerging from low—density ponds were 14.5% larger at the time of hibernation than those from high—density ponds. The mechanism for this growth advantage probably lies in the consistently higher growth rates of single toads from low—density ponds, especially during the first 3 wk after metamorphosis. Second, survival in group containers was higher for toads from low—density ponds, especially during the first few weeks after metamorphosis when most deaths involved toads from high—density ponds. These results support a carry—over effect between larval history and subsequent performance in an organism with a complex life cycle. Infection with lungworms had no detectable effect on metamorph growth or survival. This result contrasts earlier studies on this system, possibly due to the relatively low worm burdens or low statistical power. Yet, the results may also indicate that the predicted impact of infection on hosts, especially those limited by resources, is not as straightforward as theoretical studies suggest.
Although results from field surveys have linked parasites to oxidative stress in their fish hosts, direct evidence involving experimentally infected hosts is lacking. We evaluated the effects of ...experimental infections with larval trematodes on induction of oxidative stress in fathead minnows, Pimephales promelas. Juvenile fish were exposed in the laboratory to the larvae (cercariae) of 2 species of trematode: Ornithodiplostomum sp. that develops in the liver, and O. ptychocheilus that develops in the brain. For Ornithodiplostomum sp., lipid peroxidation concentration in liver tissue increased 5 days after exposure and remained higher than controls until the end of the experiment at 28 days. For O. ptychocheilus, liver lipid peroxidation concentration was higher than controls at 5 days, but not thereafter. Sustained elevation in lipid peroxidation concentration for the liver trematode may be explained by direct tissue damage caused by developing larvae in the liver, or by an immune response. These experimental results support those from field studies, indicating that the lipid peroxidation assay may be an effective biomonitor for parasite-induced oxidative stress in fish, and that the nature of the oxidative stress response is species and/or tissue specific.
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