Northern host-parasite assemblages: history and biogeography on the borderlands of episodic climate and environmental transition

First report of Strongylidae nematode from pilot whale (Globicephala macrorhynchus) by molecular analysis reveals the cosmopolitan distribution of the taxon

This study investigates the identification, genetic composition, and placement in the evolutionary tree of a particular nematode species found in a short-finned pilot whale in the Gulf of Thailand. To accomplish this, we utilized various methods, including microscopic observations, molecular techniques, and comparative analyses to better understand the characteristics of this parasite. Initially, we concentrated on studying the 18s rDNA sequence through nested PCR, resulting in a 774-bp product. After conducting a BLASTn analysis, we discovered that there were only a few sequences in the GeneBank that shared similarities with our nematode, particularly with Cyathostomum catinatum, although the percent identity was relatively low. To confirm the uniqueness of our sequence, we constructed a phylogenetic tree that demonstrated a distinct branch for our nematode, suggesting significant genetic differentiation from C. catinatum. Additionally, we sequenced a 399-bp section of the ITS2 gene using PCR, and the resulting data showed a close association with the Strongylidae family, specifically with Cylicocyclus insigne. This was further confirmed by BLASTn and CD-HIT-est results, which indicated a 99 and ~94% sequence homology with C. insigne, respectively. The ITS2 phylogenetic tree also supported the position of our isolated sequence within the Strongylidae family, clustering closely with C.insigne. Our findings shed light on the genetic connections, taxonomy, and evolutionary trends within the Strongylidae family, with a particular focus on the widespread nature of the Cylicocyclus genus. This study emphasizes the importance of utilizing molecular techniques and interdisciplinary approaches to gain insight into nematode diversity, evolution, and ecological dynamics in marine environments.

Late Cenozoic History And The Role Of Beringia In Assembling A Holarctic Cestode Species Complex

The dynamic climate history that drove sea level fluctuation during past glacial periods mediated the movement of organisms between Asia and North America via the Bering Land Bridge. Investigations of the biogeographic histories of small mammals and their parasites demonstrate facets of a complex history of episodic geographic colonization and refugial isolation that structured diversity across the Holarctic. We use a large multi-locus nuclear DNA sequence dataset to robustly resolve relationships within the cestode genus Arostrilepis (Cyclophyllidea: Hymenolepididae), a widespread parasite of predominantly arvicoline rodents (voles, lemmings). Using this phylogeny, we confirm that several Asian Arostrilepis lineages colonized North America during up to four distinct glacial periods in association with different rodent hosts, consistent with taxon-pulse dynamics. A previously inferred westward dispersal across the land bridge is rejected. We also refine interpretations of past host colonization, providing evidence for several distinct episodes of expanding host range, which probably contributed to diversification by Arostrilepis. Finally, Arostrilepis is shown to be paraphyletic with respect to Hymenandrya thomomyis, a parasite of pocket gophers, confirming that ancient Arostrilepis species colonized new host lineages upon arriving in North America.

Prey-mimetism in cercariae of Apatemon (Digenea, Strigeidae) in freshwater in northern latitudes

Cercariae, the free-living larval stages of trematodes, have adopted an amazing variety of transmission strategies. One of them is prey-mimetism, i.e. cercariae mimicking prey to attract motile hosts to be eaten. In a period between 2002 and 2019, we examined small planorbid snails, Bathyomphalus contortus, Gyraulus parvus and Planorbis planorbis from lakes in Finland and Iceland and from the Curonian Lagoon in Lithuania. Cercariae with conspicuously enlarged tails and unusual swimming behaviour, likely mimicking invertebrate prey, were detected and studied by the use of morphological and molecular (cox1, ITS1-5.8S-ITS2 and 28S rDNA) methods. Cercariae of two species belonging to the genus Apatemon (Strigeidae) were recognised. We consider Apatemon sp. 5 ex P. planorbis from the Curonian Lagoon identical to Cercaria globocaudata U. Szidat, 1940. Cercariae ex G. parvus from Iceland and ex B. contortus from Finland were conspecific, and we named them Apatemon sp. 6; these cercariae could not be associated with any known species. For the first time, we verified that cercariae of the Bulbocauda group belong to the genus Apatemon. We provide a mini-review on records of furcocercariae of the family Strigeidae with enlarged tails reported in freshwaters of the northern hemisphere and reveal that it is not only Apatemon but also Australapatemon and most likely Strigea which belong to the Bulbocauda group, rendering it a purely ecological assemblage. Understanding which invertebrate swimming behaviour these cercariae are mimicking will enhance our knowledge of the processes behind trematode transmission and will help to assess evolutionary pathways of host-finding strategies in trematodes.

Historical dispersal and host-switching formed the evolutionary history of a globally distributed multi-host parasite - The Ligula intestinalis species complex

Studies on parasite biogeography and host spectrum provide insights into the processes driving parasite diversification. Global geographical distribution and a multi-host spectrum make the tapeworm Ligula intestinalis a promising model for studying both the vicariant and ecological modes of speciation in parasites. To understand the relative importance of host association and biogeography in the evolutionary history of this tapeworm, we analysed mtDNA and reduced-represented genomic SNP data for a total of 139 specimens collected from 18 fish-host genera across a distribution range representing 21 countries. Our results strongly supported the existence of at least 10 evolutionary lineages and estimated the deepest divergence at approximately 4.99-5.05 Mya, which is much younger than the diversification of the fish host genera and orders. Historical biogeography analyses revealed that the ancestor of the parasite diversified following multiple vicariance events and was widespread throughout the Palearctic, Afrotropical, and Nearctic between the late Miocene and early Pliocene. Cyprinoids were inferred as the ancestral hosts for the parasite. Later, from the late Pliocene to Pleistocene, new lineages emerged following a series of biogeographic dispersal and host-switching events. Although only a few of the current Ligula lineages show narrow host-specificity (to a single host genus), almost no host genera, even those that live in sympatry, overlapped between different Ligula lineages. Our analyses uncovered the impact of historical distribution shifts on host switching and the evolution of host specificity without parallel host-parasite co-speciation. Historical biogeography reconstructions also found that the parasite colonized several areas (Afrotropical and Australasian) much earlier than was suggested by only recent faunistic data.

High overlap of zoonotic helminths between wild mammalian predators and rural dogs - an emerging One Health concern?

The concept of One Health emphasizes the interdependence of human, animal and environmental health and is of growing significance, in part owing to the problems related to emerging infectious diseases of wildlife origin. Wild mammalian predators are a potential risk factor for transmission of zoonotic pathogens to domesticated animals and humans. This is especially relevant in rural areas, where transmission of zoonotic pathogens can occur particularly efficiently when free-ranging dogs are present. The main aim of this study was to determine helminth infections among wild mammalian predators and evaluate the overlap between helminth faunas of wild mammals and dogs. Scat samples of predators were collected in coastal areas of Western Estonia and genetic methodology applied for the correct identification of predator species from their scat. Parasitic helminths of mammalian predators in the scat samples were analysed and compared with dog data from a previous study. High helminth prevalence (~90%) was found in dominant predator species in the area, namely the red fox (Vulpes vulpes) and golden jackal (Canis aureus). Moreover, the helminth fauna of both wild species, including potentially zoonotic helminths, overlapped largely with that of rural dogs in the same area. The results, together with the ones from earlier parasitological studies among humans in Estonia, emphasize the potential risk of pathogen transmission from wild mammalian predators to dogs and from dogs to humans, making parasitic diseases of wildlife a One Health concern.

Citellinema (Nematoda: Heligmosomidae) from North America with descriptions of 2 new species from the red squirrel Tamiasciurus hudsonicus and 1 from the Canadian woodchuck, Marmota monax

Citellinema Hall, 1918 includes 6 valid species of gastrointestinal nematodes of sciurids. Two species occur in the Palearctic and 4 in the Nearctic, 3 of which occur minimally across Colorado, Idaho and Oregon and 1, Citellinema bifurcatum, has a wide distribution across North America. Members of the genus are didelphic, possess a cephalic vesicle, a terminal spine-like process in females and feature robust spicules, consisting of a proximal end fused and semicylindrical shaft connected to a lamina supported by 2 terminal filiform processes. Typically, the size of the spicules is used to differentiate species. As part of the Beringian Coevolution Project, specimens provisionally identified as C. bifurcatum were collected through intensive field sampling of mammals and associated parasites from across localities spanning the Holarctic. These specimens revealed considerable genetic variability at both mitochondrial and nuclear loci, supporting the identification of deeply divergent clades. Examination of these new specimens, along with the holotypes of C. bifurcatum and Citellinema quadrivittati indicates that Citellinema monacis (previously synonymized with C. bifurcatum) should be resurrected and 3 additional species described. We suggest that the apparent bifurcated nature of the spicule should be considered a generic diagnostic trait, while the proportional length of the lamina relative to that of the spicule is used as a specific character. We demonstrate the critical need for continued inventory of often poorly known assemblages of hosts and parasites, contributing to a growing baseline of archival specimens, collections and information that make explorations of faunal structure and diversity possible.

Concordant phylogeographic responses to large-scale coastal disturbance in intertidal macroalgae and their epibiota

Major ecological disturbance events can provide opportunities to assess multispecies responses to upheaval. In particular, catastrophic disturbances that regionally extirpate habitat-forming species can potentially influence the genetic diversity of large numbers of codistributed taxa. However, due to the rarity of such disturbance events over ecological timeframes, the genetic dynamics of multispecies recolonization processes have remained little understood. Here, we use single nucleotide polymorphism (SNP) data from multiple coastal species to track the dynamics of cocolonization events in response to ancient earthquake disturbance in southern New Zealand. Specifically, we use a comparative phylogeographic approach to understand the extent to which epifauna (with varying ecological associations with their macroalgal hosts) share comparable spatial and temporal recolonization patterns. Our study reveals concordant disturbance-related phylogeographic breaks in two intertidal macroalgal species along with two associated epibiotic species (a chiton and an isopod). By contrast, two codistributed species, one of which is an epibiotic amphipod and the other a subtidal macroalga, show few, if any, genetic effects of palaeoseismic coastal uplift. Phylogeographic model selection reveals similar post-uplift recolonization routes for the epibiotic chiton and isopod and their macroalgal hosts. Additionally, codemographic analyses support synchronous population expansions of these four phylogeographically similar taxa. Our findings indicate that coastal paleoseismic activity has driven concordant impacts on multiple codistributed species, with concerted recolonization events probably facilitated by macroalgal rafting. These results highlight that high-resolution comparative genomic data can help reconstruct concerted multispecies responses to recent ecological disturbance.

Presence of a cryptic Onchocerca species in black flies of northern California, USA

Background

Black flies (Diptera: Simuliidae) serve as arthropod vectors for various species of Onchocerca (Nematoda: Onchocercidae) that may be associated with disease in humans, domestic animals, and wildlife. The emergence of zoonotic Onchocerca lupi in North America and reports of cervid-associated zoonotic onchocerciasis by Onchocerca jakutensis highlight the need for increased entomological surveillance. In addition, there is mounting evidence that Onchocerca diversity in North America is far greater than previously thought, currently regarded as Onchocerca cervipedis species complex. This study reports new geographic records and black fly vector associations of an uncharacterized Onchocerca species.

Methods

To better understand the biodiversity and geographic distribution of Onchocerca, 485 female black flies (2015: 150, 2016: 335) were collected using CO₂-baited traps from February to October 2015–2016 in Lake County, northern California, USA. Individual flies were morphologically identified and pooled (≤ 10 individuals) by species, collection date, and trap location. Black fly pools were processed for DNA extraction, and subsequent PCR and sequencing targeting of the NADH dehydrogenase subunit 5 gene of filarioids.

Results

Among the pools of black flies, there were 158 individuals of Simulium tescorum (2015: 57, 2016: 101), 302 individuals of Simulium vittatum (sensu lato [s.l.]) (2015: 82, 2016: 220), 16 individuals of Simulium clarum “black” phenotype (2015: 5, 2016: 11), and 13 individuals of S. clarum “orange” phenotype (2015: 6, 2016: 7). PCR analysis revealed the percentage of filarioid-positive pools were 7.50% (n = 3) for S. tescorum, 3.75% (n = 3) for S. vittatum (s.l., likely S. tribulatum), 7.69% (n = 1) for S. clarum “black” phenotype, and no positives for S. clarum “orange” phenotype. Genetic distance and phylogenetic analyses suggest that the northern California Onchocerca isolates belong to the same species reported in black flies from southern California (average pairwise comparison: 0.32%), and seem closely related to Onchocerca isolates of white-tailed deer from upstate New York (average pairwise comparison: 2.31%).

Conclusion

A cryptic Onchocerca species was found in Lake County, California, and may be a part of a larger, continentally distributed species complex rather than a single described species of North America. In addition, there are at least three putative vectors of black flies (S. clarum, S. tescorum, S. vittatum) associated with this cryptic Onchocerca species. A comprehensive reassessment of North American Onchocerca biodiversity, host, and geographic range is necessary.

Graphical abstract

Characterizing parasitic nematode faunas in faeces and soil using DNA metabarcoding

Background

Gastrointestinal parasitic nematodes can impact fecundity, development, behaviour, and survival in wild vertebrate populations. Conventional monitoring of gastrointestinal parasitic nematodes in wild populations involves morphological identification of eggs, larvae, and adults from faeces or intestinal samples. Adult worms are typically required for species-level identification, meaning intestinal material from dead animals is needed to characterize the nematode community with high taxonomic resolution. DNA metabarcoding of environmental samples is increasingly used for time- and cost-effective, high-throughput biodiversity monitoring of small-bodied organisms, including parasite communities. Here, we evaluate the potential of DNA metabarcoding of faeces and soil samples for non-invasive monitoring of gastrointestinal parasitic nematode communities in a wild ruminant population.

Methods

Faeces and intestines were collected from a population of wild reindeer, and soil was collected both from areas showing signs of animal congregation, as well as areas with no signs of animal activity. Gastrointestinal parasitic nematode faunas were characterized using traditional morphological methods that involve flotation and sedimentation steps to concentrate nematode biomass, as well as using DNA metabarcoding. DNA metabarcoding was conducted on bulk samples, in addition to samples having undergone sedimentation and flotation treatments.

Results

DNA metabarcoding and morphological approaches were largely congruent, recovering similar nematode faunas from all samples. However, metabarcoding provided higher-resolution taxonomic data than morphological identification in both faeces and soil samples. Although concentration of nematode biomass by sedimentation or flotation prior to DNA metabarcoding reduced non-target amplification and increased the diversity of sequence variants recovered from each sample, the pretreatments did not improve species detection rates in soil and faeces samples.

Conclusions

DNA metabarcoding of bulk faeces samples is a non-invasive, time- and cost-effective method for assessing parasitic nematode populations that provides data with comparable taxonomic resolution to morphological methods that depend on parasitological investigations of dead animals. The successful detection of parasitic gastrointestinal nematodes from soils demonstrates the utility of this approach for mapping distribution and occurrences of the free-living stages of gastrointestinal parasitic nematodes.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04935-8.

Zoonotic pathogens in wild muskoxen (Ovibos moschatus) and domestic sheep (Ovis aries) from Greenland

The present study aimed to estimate the prevalence of zoonotic pathogens Giardia duodenalis, Cryptosporidium spp., Toxoplasma gondii and Erysipelothrix in muskoxen (Ovibos moschatus) and sheep (Ovis aries) from Greenland. In 2017 and 2018, faecal samples were collected from wild muskoxen from three distinct populations (Zackenberg, Kangerlussuaq, and Ivittuut) and from domestic sheep from southwest Greenland. Blood samples were collected from muskoxen from Kangerlussuaq and Ivittuut and from sheep. Faecal samples were tested for specific DNA of G. duodenalis and Cryptosporidium spp., and blood samples were tested for antibodies against T. gondii and Erysipelothrix. The estimated prevalence of G. duodenalis was 0% (0/58), 17% (7/41) and 0% (0/55) in muskoxen from Zackenberg, Kangerlussuaq and Ivittuut, respectively, and 37% (16/43) in sheep. The estimated prevalence of Cryptosporidium was 0% (0/58), 2% (1/41), 7% (4/55) in muskoxen from Zackenberg, Kangerlussuaq, Ivittuut, respectively, and 2% (1/43) in sheep. Neither Giardia nor Cryptosporidium were detected in winter samples (0/78). Of the positive samples, Giardia from one muskox sample only was successfully typed as G. duodenalis assemblage A, and Cryptosporidium from two muskoxen was successfully typed as C. parvum, subtype IIdA20G1e. The estimated T. gondii seroprevalence was 2% (1/44) and 0% (0/8) in muskoxen from Kangerlussuaq and Ivittuut, respectively, and 1% (1/155) in sheep. The estimated Erysipelothrix seroprevalence was 2% (1/45) and 13% (1/8) in muskoxen from Kangerlussuaq and Ivittuut, respectively, and 7% (10/150) in sheep. The results of this study add to the scarce knowledge on zoonotic pathogens in the Arctic.

Diversity of echinostomes (Digenea: Echinostomatidae) in their snail hosts at high latitudes

The biodiversity of freshwater ecosystems globally still leaves much to be discovered, not least in the trematode parasite fauna they support. Echinostome trematode parasites have complex, multiple-host life-cycles, often involving migratory bird definitive hosts, thus leading to widespread distributions. Here, we examined the echinostome diversity in freshwater ecosystems at high latitude locations in Iceland, Finland, Ireland and Alaska (USA). We report 14 echinostome species identified morphologically and molecularly from analyses of nad1 and 28S rDNA sequence data. We found echinostomes parasitising snails of 11 species from the families Lymnaeidae, Planorbidae, Physidae and Valvatidae. The number of echinostome species in different hosts did not vary greatly and ranged from one to three species. Of these 14 trematode species, we discovered four species (Echinoparyphium sp. 1, Echinoparyphium sp. 2, Neopetasiger sp. 5, and Echinostomatidae gen. sp.) as novel in Europe; we provide descriptions for the newly recorded species and those not previously associated with DNA sequences. Two species from Iceland (Neopetasiger islandicus and Echinoparyphium sp. 2) were recorded in both Iceland and North America. All species found in Ireland are new records for this country. Via an integrative taxonomic approach taken, both morphological and molecular data are provided for comparison with future studies to elucidate many of the unknown parasite life cycles and transmission routes. Our reports of species distributions spanning Europe and North America highlight the need for parasite biodiversity assessments across large geographical areas.

The Legacy of Recurrent Introgression during the Radiation of Hares

Hybridization may often be an important source of adaptive variation, but the extent and long-term impacts of introgression have seldom been evaluated in the phylogenetic context of a radiation. Hares (Lepus) represent a widespread mammalian radiation of 32 extant species characterized by striking ecological adaptations and recurrent admixture. To understand the relevance of introgressive hybridization during the diversification of Lepus, we analyzed whole exome sequences (61.7 Mb) from 15 species of hares (1-4 individuals per species), spanning the global distribution of the genus, and two outgroups. We used a coalescent framework to infer species relationships and divergence times, despite extensive genealogical discordance. We found high levels of allele sharing among species and show that this reflects extensive incomplete lineage sorting and temporally layered hybridization. Our results revealed recurrent introgression at all stages along the Lepus radiation, including recent gene flow between extant species since the last glacial maximum but also pervasive ancient introgression occurring since near the origin of the hare lineages. We show that ancient hybridization between northern hemisphere species has resulted in shared variation of potential adaptive relevance to highly seasonal environments, including genes involved in circadian rhythm regulation, pigmentation, and thermoregulation. Our results illustrate how the genetic legacy of ancestral hybridization may persist across a radiation, leaving a long-lasting signature of shared genetic variation that may contribute to adaptation. [Adaptation; ancient introgression; hybridization; Lepus; phylogenomics.].

Emerging infectious disease: An underappreciated area of strategic concern for food security

Emerging infectious diseases (EIDs) increasingly threaten global food security and public health. Despite technological breakthroughs, we are losing the battle with (re)emerging diseases as treatment costs and production losses rise. A horizon scan of diseases of crops, livestock, seafood and food-borne illness suggests these costs are unsustainable. The paradigm of coevolution between pathogens and particular hosts teaches that emerging diseases occur only when pathogens evolve specific capacities that allow them to move to new hosts. EIDs ought to be rare and unpredictable, so crisis response is the best we can do. Alternatively, the Stockholm Paradigm suggests that the world is full of susceptible but unexposed hosts that pathogens could infect, given the opportunity. Global climate change, globalized trade and travel, urbanization and land-use changes (often associated with biodiversity loss) increase those opportunities, making EID frequent. We can, however, anticipate their arrival in new locations and their behaviour once they have arrived. We can 'find them before they find us', mitigating their impacts. The DAMA (Document, Assess, Monitor, Act) protocol alters the current reactive stance and embodies proactive solutions to anticipate and mitigate the impacts of EID, extending human and material resources and buying time for development of new vaccinations, medications and control measures.

When parasites persist: tapeworms survive host extinction and reveal waves of dispersal across Beringia

Investigations of intercontinental dispersal between Asia and North America reveal complex patterns of geographic expansion, retraction and isolation, yet historical reconstructions are largely limited by the depth of the record that is retained in patterns of extant diversity. Parasites offer a tool for recovering deep historical insights about the biosphere, improving the resolution of past community-level interactions. We explored biogeographic hypotheses regarding the history of dispersal across Beringia, the region intermittently linking Asia and North America, through large-scale multi-locus phylogenetic analyses of the genus Schizorchis, an assemblage of host-specific cestodes in pikas (Lagomorpha: Ochotonidae). Our genetic data support palaeontological evidence for two separate geographic expansions into North America by Ochotona in the late Tertiary, a history that genomic evidence from extant pikas does not record. Pikas descending from the first colonization of Miocene age persisted into the Pliocene, subsequently coming into contact with a second wave of Nearctic colonists from Eurasia before going extinct. Spatial and temporal overlap of historically independent pika populations provided a window for host colonization, allowing persistence of an early parasite lineage in the contemporary fauna following the extinction of its ancestral hosts. Empirical evidence for ancient 'ghost assemblages' of hosts and parasites demonstrates how complex mosaic faunas are assembled in the biosphere through episodes of faunal mixing encompassing parasite lineages across deep and shallow time.

High parasite diversity in the amphipod Gammarus lacustris in a subarctic lake

Amphipods are often key species in aquatic food webs due to their functional roles in the ecosystem and as intermediate hosts for trophically transmitted parasites. Amphipods can also host many parasite species, yet few studies address the entire parasite community of a gammarid population, precluding a more dynamic understanding of the food web. We set out to identify and quantify the parasite community of Gammarus lacustris to understand the contributions of the amphipod and its parasites to the Takvatn food web. We identified seven parasite taxa: a direct life cycle gregarine, Rotundula sp., and larval stages of two digenean trematode genera, two cestodes, one nematode, and one acanthocephalan. The larval parasites use either birds or fishes as final hosts. Bird parasites predominated, with trematode Plagiorchis sp. having the highest prevalence (69%) and mean abundance (2.7). Fish parasites were also common, including trematodes Crepidostomum spp., nematode Cystidicola farionis, and cestode Cyathocephalus truncatus (prevalences 13, 6, and 3%, respectively). Five parasites depend entirely on G. lacustris to complete their life cycle. At least 11.4% of the overall parasite diversity in the lake was dependent on G. lacustris, and 16% of the helminth diversity required or used the amphipod in their life cycles. These dependencies reveal that in addition to being a key prey item in subarctic lakes, G. lacustris is also an important host for maintaining parasite diversity in such ecosystems.

Range expansion of muskox lungworms track rapid arctic warming: implications for geographic colonization under climate forcing

Rapid climate warming in the Arctic results in multifaceted disruption of biodiversity, faunal structure, and ecosystem health. Hypotheses have linked range expansion and emergence of parasites and diseases to accelerating warming globally but empirical studies demonstrating causality are rare. Using historical data and recent surveys as baselines, we explored climatological drivers for Arctic warming as determinants of range expansion for two temperature-dependent lungworms, Umingmakstrongylus pallikuukensis and Varestrongylus eleguneniensis, of muskoxen (Ovibos moschatus) and caribou (Rangifer tarandus), in the Canadian Arctic Archipelago from 1980 through 2017. Our field data shows a substantial northward shift of the northern edge of the range for both parasites and increased abundance across the expanded ranges during the last decade. Mechanistic models parameterized with parasites’ thermal requirements demonstrated that geographical colonization tracked spatial expansion of permissive environments, with a temporal lag. Subtle differences in life histories, thermal requirements of closely related parasites, climate oscillations and shifting thermal balances across environments influence faunal assembly and biodiversity. Our findings support that persistence of host-parasite assemblages reflects capacities of parasites to utilize host and environmental resources in an ecological arena of fluctuating opportunity (alternating trends in exploration and exploitation) driving shifting boundaries for distribution across spatial and temporal scales.

Adaptations, life-history traits and ecological mechanisms of parasites to survive extremes and environmental unpredictability in the face of climate change

Climate change is increasing weather unpredictability, causing more intense, frequent and longer extreme events including droughts, precipitation, and both heat and cold waves. The performance of parasites, and host-parasite interactions, under these unpredictable conditions, are directly influenced by the ability of parasites to cope with extremes and their capacity to adapt to the new conditions. Here, we review some of the structural, behavioural, life history and ecological characteristics of parasitic nematodes that allow them to persist and adapt to extreme and changing environmental conditions. We focus primarily, but not exclusively, on parasitic nematodes in the Arctic, where temperature extremes are pronounced, climate change is happening most rapidly, and changes in host-parasite interactions are already documented. We discuss how life-history traits, phenotypic plasticity, local adaptation and evolutionary history can influence the short and long term response of parasites to new conditions. A detailed understanding of the complex ecological processes involved in the survival of parasites in extreme and changing conditions is a fundamental step to anticipate the impact of climate change in parasite dynamics.

Global Prevalence Estimates of Toxascaris leonina Infection in Dogs and Cats

Toxascaris leonina is an ascaridoid nematode of dogs and cats; this parasite affects the health of these animals. This study estimated the global prevalence of Ta. leonina infection in dogs and cats using random effects meta-analysis as well as subgroup, meta-regression and heterogeneity analyses. The data were stratified according to geographical region, the type of dogs and cats and environmental variables. A quantitative analysis of 135 published studies, involving 119,317 dogs and 25,364 cats, estimated prevalence rates of Ta. leonina in dogs and cats at 2.9% and 3.4%, respectively. Prevalence was highest in the Eastern Mediterranean region (7.2% for dogs and 10.0% for cats) and was significantly higher in stray dogs (7.0% vs. 1.5%) and stray cats (7.5% vs. 1.8%) than in pets. The findings indicate that, worldwide, ~26 million dogs and ~23 million cats are infected with Ta. leonina; these animals would shed substantial numbers of Ta. leonina eggs into the environment each year and might represent reservoirs of infection to other accidental or paratenic hosts. It is important that populations of dogs and cats as well as other canids and felids be monitored and dewormed for Ta. leonina and (other) zoonotic helminths.

Pan-American Trypanosoma (Megatrypanum) trinaperronei n. sp. in the white-tailed deer Odocoileus virginianus Zimmermann and its deer ked Lipoptena mazamae Rondani, 1878: morphological, developmental and phylogeographical characterisation

Background

The subgenus Megatrypanum Hoare, 1964 of Trypanosoma Gruby, 1843 comprises trypanosomes of cervids and bovids from around the world. Here, the white-tailed deer Odocoileus virginianus (Zimmermann) and its ectoparasite, the deer ked Lipoptena mazamae Rondani, 1878 (hippoboscid fly), were surveyed for trypanosomes in Venezuela.

Results

Haemoculturing unveiled 20% infected WTD, while 47% (7/15) of blood samples and 38% (11/29) of ked guts tested positive for the Megatrypanum-specific TthCATL-PCR. CATL and SSU rRNA sequences uncovered a single species of trypanosome. Phylogeny based on SSU rRNA and gGAPDH sequences tightly cluster WTD trypanosomes from Venezuela and the USA, which were strongly supported as geographical variants of the herein described Trypanosoma (Megatrypanum) trinaperronei n. sp. In our analyses, the new species was closest to Trypanosoma sp. D30 from fallow deer (Germany), both nested into TthII alongside other trypanosomes from cervids (North American elk and European fallow, red and sika deer), and bovids (cattle, antelopes and sheep). Insights into the life-cycle of T. trinaperronei n. sp. were obtained from early haemocultures of deer blood and co-culture with mammalian and insect cells showing flagellates resembling Megatrypanum trypanosomes previously reported in deer blood, and deer ked guts. For the first time, a trypanosome from a cervid was cultured and phylogenetically and morphologically (light and electron microscopy) characterised.

Conclusions

In the analyses based on SSU rRNA, gGAPDH, CATL and ITS rDNA sequences, neither cervids nor bovids trypanosomes were monophyletic but intertwined within TthI and TthII major phylogenetic lineages. One host species can harbour more than one species/genotype of trypanosome, but each trypanosome species/genotype was found in a single host species or in phylogenetically closely related hosts. Molecular evidence that L. mazamae may transmit T. trinaperronei n. sp. suggests important evolutionary constraints making tight the tripartite T. trinaperronei-WTD-deer ked association. In a plausible evolutionary scenario, T. trinaperronei n. sp. entered South America with North American white-tailed deer at the Pliocene-Pleistocene boundary following the closure of the Panama Isthmus.

Phenotypic plasticity and local adaptation in freeze tolerance: Implications for parasite dynamics in a changing world

Marshallagia marshalli is a multi-host gastrointestinal nematode that infects a variety of artiodactyl species from temperate to Arctic latitudes. Eggs of Marshallagia are passed in host faeces and develop through three larval stages (L1, L2, and L3) in the environment. Although eggs normally hatch as L1s, they can also hatch as L3s. We hypothesised that this phenotypic plasticity in hatching behaviour may improve fitness in subzero and highly variable environments, and this may constitute an evolutionary advantage under current climate change scenarios. To test this, we first determined if the freeze tolerance of different free-living stages varied at different temperatures (-9 °C, -20 °C and -35 °C). We then investigated if there were differences in freeze tolerance of M. marshalli eggs sourced from three discrete, semi-isolated, populations of wild bighorn and thinhorn sheep living in western North America (latitudes: 40°N, 50°N, 64°N). The survival rates of eggs and L3s were significantly higher than L1s at -9 °C and -20 °C, and survival of all three stages decreased significantly with increasing freeze duration and decreasing temperature. The survival of unhatched L1s was significantly higher than the survival of hatched L1s. There was no evidence of local thermal adaptation in freeze tolerance among eggs from different locations. We conclude that developing to the L3 in the egg may result in a fitness advantage for M. marshalli, with the egg protecting the more vulnerable L1 under freezing conditions. This phenotypic plasticity in life-history traits of M. marshalli might be an important capacity, a potential exaptation capable of enhancing parasite fitness under temperature extremes.

The biogeography of the caribou lungworm, Varestrongylus eleguneniensis (Nematoda: Protostrongylidae) across northern North America

Varestrongylus eleguneniensis (Nematoda; Protostrongylidae) is a recently described species of lungworm that infects caribou (Rangifer tarandus), muskoxen (Ovibos moschatus) and moose (Alces americanus) across northern North America. Herein we explore the geographic distribution of V. eleguneniensis through geographically extensive sampling and discuss the biogeography of this multi-host parasite. We analyzed fecal samples of three caribou subspecies (n = 1485), two muskox subspecies (n = 159), and two moose subspecies (n = 264) from across northern North America. Protostrongylid dorsal-spined larvae (DSL) were found in 23.8%, 73.6%, and 4.2% of these ungulates, respectively. A portion of recovered DSL were identified by genetic analyses of the ITS-2 region of the nuclear rDNA or the cytochrome oxidase c subunit I (COI) region of the mtDNA. We found V. eleguneniensis widely distributed among caribou and muskox populations across most of their geographic prange in North America but it was rare in moose. Parelaphostrongylus andersoni was present in caribou and moose and we provide new geographic records for this species. This study provides a substantial expansion of the knowledge defining the current distribution and biogeography of protostrongylid nematodes in northern ungulates. Insights about the host and geographic range of V. eleguneniensis can serve as a geographically extensive baseline for monitoring current distribution and in anticipating future biogeographic scenarios under a regime of accelerating climate and anthropogenic perturbation.

Discovery of Arostrilepis tapeworms (Cyclophyllidea: Hymenolepididae) and new insights for parasite species diversity from Eastern North America

Species of the genus Arostrilepis were discovered and definitively identified for the first time in rodents from geographically disparate localities along the Appalachian Mountain range of eastern North America (West Virginia, Virginia, and Maine). These are the first confirmed records for species of Arostrilepis occurring east of the Rocky Mountains and the Mississippi River in North America. Arostrilepis gardneri n. sp. is described on the basis of specimens obtained from two phylogenetically divergent rodent hosts: Southern Red-Backed Vole Myodes gapperi (Cricetidae: Arvicolinae) (from West Virginia) and the Woodland Jumping Mouse Napaeozapus insignis (Dipodidae: Zapodinae) (West Virginia, Virginia, and Maine). Additionally, in a mixed infection, specimens of Arostrilepis insperata n. sp. were also found in a Southern Red-Backed Vole from West Virginia. These previously unknown species are primarily distinguished from congeners based on shape, dimensions, and spination (pattern, shape, and size of spines) of the cirrus. Specimens of A. gardneri n. sp. are further characterized by the relative position and length of the cirrus-sac, arrangement of the testes, and relative size of the external seminal vesicle and seminal receptacle. Specimens of A. insperata n. sp. are structurally most similar to A. macrocirrosa from the western Nearctic and Palearctic but with consistently greater dimensions for the cirrus-sac, testes, and seminal receptacle. Phylogenetic analysis of Arostrilepis spp. using partial sequences of the mitochondrial cytochrome b gene and the nuclear second ribosomal internal transcribed spacer strongly supported the status of A. gardneri n. sp. and A. insperata n. sp. within an unresolved clade of congeners in Red-Backed Voles (Myodini and species of Myodes). Our observations extend the known geographic distribution for species of Arostrilepis to the Appalachian Mountains in either a disjunct or possibly continuous but patchy range across North America. Prior observations, summarizing field and museum collections, had suggested that geographic ranges for a diverse assemblage of Arostrilepis in North America were largely restricted to the north-western region of the continent, with historical connections to Beringia and Eurasia. Recognition of a more extensive distribution is consistent with a history of episodic biotic expansion and isolation under a dynamic of taxon pulses for arvicoline rodents and an associated parasite fauna in the Nearctic during the Quaternary. Occurrence in a dipodid rodent represents an event of host colonization from an arvicoline source.

On the geographic genetic variants of the cestode Echinococcus multilocularis with reference to the original descriptions from Bowles et al. (1992) and Bowles and McManus (1993), and their use

Alveolar echinococcosis, caused by the larval stages of the tapeworm Echinococcus multilocularis (Leuckart, 1863), is of increasing concern in the northern hemisphere. Most cases of alveolar echinococcosis (excluding Alaska) appear to be linked with European and Asian genotypes that highlight the need for a more precise delimiting of their actual distribution and tracing historical episodes of their translocations and introductions into new areas. We have herein summarized previous available research studies, which mentioned firstly described geographic M1/M2 variants of E. multilocularis using molecular tools (established by sequencing of mitochondrial genes cox1, 366 bp and nad1, 471 bp), in an attempt to consolidate their correct affiliations with the geographic origin in sense of the original description from the early 1990´s. Since 2009, inverted designations (M1 named as M2 and vice versa) are being prevailing in research literature (we found ten erroneous vs. three correct classifications) that might bias genetic interpretation of comparative data in specific cases. When comparing M1/M2 profiles to those obtained from mitochondrial evidences over the last decades, the phylogenetic analysis revealed that the M1 strain (originally described from China, Alaska, North America) grouped with the Asian clade of E. multilocularis more recently established, whereas the M2 strain (described from the German vole) had a specific structure, in cox1 clustering with the North American clade. It is presumed that events of intercontinental expansion and isolation covering glacial and interglacial periods during the late Pleistocene have likely accounted for the transmission of this discrete genotype from Beringia into endemic area of western and central Europe via circumpolar movements of foxes.

Conservation Genomics in a Changing Arctic

Although logistically challenging to study, the Arctic is a bellwether for global change and is becoming a model for questions pertinent to the persistence of biodiversity. Disruption of Arctic ecosystems is accelerating, with impacts ranging from mixing of biotic communities to individual behavioral responses. Understanding these changes is crucial for conservation and sustainable economic development. Genomic approaches are providing transformative insights into biotic responses to environmental change, but have seen limited application in the Arctic due to a series of limitations. To meet the promise of genome analyses, we urge rigorous development of biorepositories from high latitudes to provide essential libraries to improve the conservation, monitoring, and management of Arctic ecosystems through genomic approaches.

Multi-pathogen serological survey of migratory caribou herds: A snapshot in time

Pathogens can impact host survival, fecundity, and population dynamics even when no obvious disease is observed. Few baseline data on pathogen prevalence and diversity of caribou are available, which hampers our ability to track changes over time and evaluate impacts on caribou health. Archived blood samples collected from ten migratory caribou herds in Canada and two in Greenland were used to test for exposure to pathogens that have the potential to effect population productivity, are zoonotic or are emerging. Relationships between seroprevalence and individual, population, and other health parameters were also examined. For adult caribou, the highest overall seroprevalence was for alphaherpesvirus (49%, n = 722), pestivirus (49%, n = 572) and Neospora caninum (27%, n = 452). Lower seroprevalence was found for parainfluenza virus type 3 (9%, n = 708), Brucella suis (2%, n = 758), and Toxoplasma gondii (2%, n = 706). No animal tested positive for antibodies against West Nile virus (n = 418) or bovine respiratory syncytial virus (n = 417). This extensive multi-pathogen survey of migratory caribou herds provides evidence that caribou are exposed to pathogens that may have impacts on herd health and revealed potential interactions between pathogens as well as geographical differences in pathogen exposure that could be linked to the bio-geographical history of caribou. Caribou are a keystone species and the socio-economic cornerstone of many indigenous cultures across the North. The results from this study highlight the urgent need for a better understanding of pathogen diversity and the impact of pathogens on caribou health.

Adaptations and phenotypic plasticity in developmental traits of Marshallagia marshalli

Despite the economic, social and ecological importance of the ostertagiine abomasal nematode Marshallagia marshalli, little is known about its life history traits and its adaptations to cope with environmental extremes. Conserved species-specific traits can act as exaptations that may enhance parasite fitness in changing environments. Using a series of experiments, we revealed several unique adaptations of the free-living stages of M. marshalli that differ from other ostertagiines. Eggs were isolated from the feces of bighorn sheep (Ovis canadensis) from the Canadian Rocky Mountains and were cultured at different temperatures and with different media. Hatching occurred primarily as L1s in an advanced stage of development, morphologically very similar to a L2. When cultured at 20 °C, however, 2.86% of eggs hatched as L3, with this phenomenon being significantly more common at higher temperatures, peaking at 30 °C with 28.95% of eggs hatching as L3s. After hatching, free-living larvae of M. marshalli did not feed nor grow as they matured from L1 to infective L3. These life history traits seem to be adaptations to cope with the extreme environmental conditions that Marshallagia faces across its extensive latitudinal distribution in North America and Eurasia. In order to refine the predictions of parasite dynamics under scenarios of a changing climate, basic life history traits and temperature-dependent phenotypic behaviour should be incorporated into models for parasite biology.

Prevalence and diversity of avian blood parasites in a resident northern passerine

BACKGROUND

Climate-related changes are expected to influence the prevalence and distribution of vector-borne haemosporidian parasites at northern latitudes, although baseline information about resident birds is still lacking. In this study, we investigated prevalence and genetic diversity of Plasmodium, Haemoproteus, and Leucocytozoon parasites infecting the northwestern crow (Corvus caurinus), a non-migratory passerine with unique life-history characteristics. This species occupies both intertidal and forested habitats and is subject to high prevalence of avian keratin disorder (AKD), a disease that causes gross beak deformities. Investigation of avian blood parasites in northwestern crows at sites broadly distributed across coastal Alaska provided an opportunity to evaluate specific host factors related to parasite infection status and assess geographical patterns of prevalence.

RESULTS

We used molecular methods to screen for haemosporidian parasites in northwestern crows and estimated genus-specific parasite prevalence with occupancy modeling that accounts for imperfect detection of parasite infection. We observed considerable geographical and annual variation in prevalence of Plasmodium, Haemoproteus, and Leucocytozoon, but these patterns were not correlated with indices of local climatic conditions. Our models also did not provide support for relationships between the probability of parasite infection and body condition or the occurrence of co-infections with other parasite genera or clinical signs of AKD. In our phylogenetic analyses, we identified multiple lineages of each parasite genus, with Leucocytozoon showing greater diversity than Plasmodium or Haemoproteus.

CONCLUSIONS

Results from this study expand our knowledge about the prevalence and diversity of avian blood parasites in northern resident birds as well as corvids worldwide. We detected all three genera of avian haemosporidians in northwestern crows in Alaska, although only Leucocytozoon occurred at all sites in both years. Given the strong geographical and annual variation in parasite prevalence and apparent lack of correlation with climatic variables, it appears that there are other key factors responsible for driving transmission dynamics in this region. Thus, caution is warranted when using standard climatic or geographical attributes in a predictive framework. Our phylogenetic results demonstrate lower host specificity for some lineages of Leucocytozoon than is typically reported and provide insights about genetic diversity of local haemosporidian parasites in Alaska.

Building an integrated infrastructure for exploring biodiversity: field collections and archives of mammals and parasites

Museum specimens play an increasingly important role in predicting the outcomes and revealing the consequences of anthropogenically driven disruption of the biosphere. As ecological communities respond to ongoing environmental change, host-parasite interactions are also altered. This shifting landscape of host-parasite associations creates opportunities for colonization of different hosts and emergence of new pathogens, with implications for wildlife conservation and management, public health, and other societal concerns. Integrated archives that document and preserve mammal specimens along with their communities of associated parasites and ancillary data provide a powerful resource for investigating, anticipating, and mitigating the epidemiological, ecological, and evolutionary impacts of environmental perturbation. Mammalogists who collect and archive mammal specimens have a unique opportunity to expand the scope and impact of their field work by collecting the parasites that are associated with their study organisms. We encourage mammalogists to embrace an integrated and holistic sampling paradigm and advocate for this to become standard practice for museum-based collecting. To this end, we provide a detailed, field-tested protocol to give mammalogists the tools to collect and preserve host and parasite materials that are of high quality and suitable for a range of potential downstream analyses (e.g., genetic, morphological). Finally, we also encourage increased global cooperation across taxonomic disciplines to build an integrated series of baselines and snapshots of the changing biosphere. Los especímenes de museo desempeñan un papel cada vez más importante tanto en la descripción de los resultados de la alteración antropogénica de la biosfera como en la predicción de sus consecuencias. Dado que las comunidades ecológicas responden al cambio ambiental, también se alteran las interacciones hospedador-parásito. Este panorama cambiante de asociaciones hospedador-parásito crea oportunidades para la colonización de diferentes hospedadores y para la aparición de nuevos patógenos, con implicancias en la conservación y manejo de la vida silvestre, la salud pública y otras preocupaciones de importancia para la sociedad. Archivos integrados que documentan y preservan especímenes de mamíferos junto con sus comunidades de parásitos y datos asociados, proporcionan un fuerte recurso para investigar, anticipar y mitigar los impactos epidemiológicos, ecológicos y evolutivos de las perturbaciones ambientales. Los mastozoólogos que recolectan y archivan muestras de mamíferos, tienen una oportunidad única de ampliar el alcance e impacto de su trabajo de campo mediante la recolección de los parásitos que están asociados con los organismos que estudian. Alentamos a los mastozoólogos a adoptar un paradigma de muestreo integrado y holístico y abogamos para que esto se convierta en una práctica estándarizada de la obtención de muestras para museos. Con este objetivo, proporcionamos un protocolo detallado y probado en el campo para brindar a los mastozoólogos las herramientas para recolectar y preservar materiales de parásitos y hospedadores de alta calidad y adecuados para una gran variedad de análisis subsecuentes (e.g., genéticos, morfológicos, etc.). Finalmente, también abogamos por una mayor cooperación global entre las diversas disciplinas taxonómicas para construir una serie integrada de líneas de base y registros actuales de nuestra cambiante biosfera.

A fine-scale phylogenetic assessment of digenean trematodes in central Alberta reveals we have yet to uncover their total diversity

Despite over 100 years of digenean trematode parasite species descriptions, from a wide diversity of vertebrate and invertebrate host species, our ability to recognize the diversity of trematode species within a single lake remains an incredible challenge. The most challenging aspect is the identification of species from larval stages derived from intermediate hosts, due to the disjointed data of adult worm morphological descriptions, from which species are named, and links to corresponding molecular identifiers in depauperate databases. Cryptic species also play a significant role in the challenge of linking trematode larvae to adults, species identifications, and estimating diversity. Herein, we utilize a large, longitudinal dataset of snail first-intermediate host infection data from lakes in Alberta, Canada, to infer trematode larval diversity using molecular phylogenetics and snail host associations. From our assessments, we uncover a diversity of 79 larval trematode species among just five snail host species. Only 14 species were identified to a previously described species, while the other 65 species are either cryptic or otherwise unrepresented by mitochondrial genes in GenBank. This study currently represents the largest and most diverse singular molecular survey of trematode larval fauna composed of over one thousand mitochondrial sequences. Surprisingly, rarefaction analyses indicate we have yet to capture the complete diversity of trematodes from our sampling area.

A cryptic species of Onchocerca (Nematoda: Onchocercidae) in blackflies (Simulium spp.) from southern California, USA

Background

Entomological surveillance for pathogens based on molecular screening of putative arthropod vectors such as blackflies (Diptera: Simuliidae) is becoming increasingly important. Surveillance provides a means to understand host and geographical patterns of underestimated biodiversity among North American species of Onchocerca and a pathway to identify and track expanding emergence of the zoonotic Onchocerca lupi. Herein, we have screened two blackfly species, Simulium tescorum and Simulium vittatum (s.l.), from Los Angeles County, southern California, USA for DNA of filarioid nematodes to better understand species richness and limits within the genus Onchocerca.

Methods

A total of 1056 and 378 female blackflies was collected using CO₂-baited mosquito traps from March to November of 2015 and 2016, respectively. All blackflies during 2015 were individually processed for DNA extraction and PCR targeting of the cytochrome c oxidase subunit 1 (cox1) of the mitochondrial DNA (mtDNA). Specimens of S. tescorum collected in 2016 were processed individually with heads and bodies extracted separately, whereas those of S. vittatum (s.l.) were processed in pooled samples with heads and bodies extracted separately. A subset of filarioid-positive samples from 2015 and all samples from 2016 were screened using a PCR targeting the NADH dehydrogenase subunit 5 (nad5) gene (mtDNA).

Results

In 2015, 356 S. tescorum (33.7%) and 683 S. vittatum (s.l.) (64.7%) were collected, and an additional 17 specimens were not assessed morphologically. In 2016, a total of 378 blackflies was collected. Of these, 43 (11.6%) were S. tescorum and 327 (88.4%) were S. vittatum (s.l.), and an additional 8 specimens were not assessed morphologically. In 2015, Onchocerca sequences were detected in 4.8% (n = 17) of S. tescorum samples, and only one S. vittatum (0.15%). In 2016, only a single S. vittatum pool was positive for the same cryptic Onchocerca species. In phylogenetic comparisons based on nad5, the Onchocerca sequences from California formed a clade with those isolates in white-tailed deer from upstate New York, suggesting these belong to a single widespread cryptic species.

Conclusions

An uncharacterized species of Onchocerca associated with cervid hosts was found in blackflies from southern California. Sequence data demonstrated it is likely conspecific with an unnamed species of Onchocerca previously found in white-tailed deer from upstate New York. Current data support recognition of a broad geographical distribution across North America for an apparently cryptic species of Onchocerca that is discrete from O. cervipedis, considered to be a typical filarioid among cervids. Our data suggest that this cryptic species of Onchocerca may infect subspecies of white-tailed deer (Odocoileus virginianus), and mule and black-tailed deer (Odocoileus hemionus) at temporal latitudes. The blackflies Simulium tescorum and S. vittatum (s.l.) (presumably, S. tribulatum) are putative vectors. Discovery of a cryptic complex indicates that species diversity and putative associations for definitive hosts and vectors of Onchocerca species in North America must be reassessed.

Historical biogeography among species of Varestrongylus lungworms (Nematoda: Protostrongylidae) in ungulates: episodic expansion and host colonization linking Eurasia and North America

Varestrongylus lungworms (Nematoda: Protostrongylidae) include 10 nominal species that parasitize wild and domesticated artiodactyles. Eight species are endemic to the western Palearctic and Eurasia, whereas two are limited in distribution to the Nearctic. Complex host associations, primarily among Cervidae and Bovidae (Caprinae), and biogeography were explored based on direct comparisons of parasite and host phylogenies to reveal the historical development of this fauna. Diversification among Varestrongylus species has an intricate history extending over the Pliocene and Quaternary involving episodic processes for geographic and host colonization: (1) Varestrongylus has origins in Eurasia with independent expansion events into bordering ecozones; (2) cervids are ancestral hosts; (3) the caprine-associated V. pneumonicus is basal and a result of an independent host colonization event; (4) secondary diversification, linked to sequential and independent host colonization events, occurred within cervids (V. sagittatus + V. tuvae; V. alpenae; and V. capreoli, V. alces + V. eleguneniensis); (5) at least two additional host colonization events into caprines occurred, followed or not by diversification (V. qinghaiensis + V. longispiculatus; V. capricola, respectively); (6) two independent events of geographic expansion into North America from Eurasia with cervids in the late Pliocene and early Pleistocene are postulated (V. alpenae, V. eleguneniensis). Comparisons based on phylogenetic hypotheses derived from comparative morphology and molecular inference for these nematodes are consistent with the postulated history for coevolutionary and biogeographic history. Episodes of geographic and host colonization, often in relation to rapid shifts in climate and habitat perturbation, have dominated the history of diversification of Varestrongylus.

Diversity of gastrointestinal helminths in Dall's sheep and the negative association of the abomasal nematode, Marshallagia marshalli, with fitness indicators

Gastrointestinal helminths can have a detrimental effect on the fitness of wild ungulates. Arctic and Subarctic ecosystems are ideal for the study of host-parasite interactions due to the comparatively simple ecological interactions and limited confounding factors. We used a unique dataset assembled in the early seventies to study the diversity of gastrointestinal helminths and their effect on fitness indicators of Dall’s sheep, Ovis dalli dalli, in the Mackenzie Mountains, Northwest Territories, Canada. Parasite diversity included nine species, among which the abomasal nematode Marshallagia marshalli occurred with the highest prevalence and infection intensity. The intensity of M. marshalli increased with age and was negatively associated with body condition and pregnancy status in Dall’s sheep across all the analyses performed. The intensity of the intestinal whipworm, Trichuris schumakovitschi, decreased with age. No other parasites were significantly associated with age, body condition, or pregnancy. Our study suggests that M. marshalli might negatively influence fitness of adult female Dall’s sheep.

Specific status of Echinococcus canadensis (Cestoda: Taeniidae) inferred from nuclear and mitochondrial gene sequences

The specific status of Echinococcus canadensis has long been controversial, mainly because it consists of the mitochondrial lineages G6, G7, G8 and G10 with different host affinity: G6 (camel strain) and G7 (pig strain) with domestic cycles and G8 (cervid strain) and G10 (Fennoscandian cervid strain) with sylvatic or semi-domestic cycles. There is an argument whether the mitochondrial lineages should be recognised as separate species which correspond to the biological or epidemiological aggregation. In the present study, the specific status of E. canadensis was investigated using mitochondrial DNA and single copy nuclear DNA markers. Nucleotide sequences of complete mitochondrial cytochrome c oxidase subunit 1 (cox1) and partial nuclear phosphoenolpyruvate carboxykinase (pepck) and DNA polymerase delta (pold) were determined for 48 isolates of E. canadensis collected from different hosts in a wide range of regions. The mitochondrial phylogeny of cox1 showed that all the isolates were clearly divided into three clades corresponding to G6/G7, G8 and G10. Five and three alleles were confirmed at pepck and pold loci, respectively. These alleles were generally divided into two groups corresponding to G6/G7 or G8 and G10. However, allele sharing was confirmed among individuals belonging to different lineages. The allele sharing occurred primarily in regions where different mitochondrial DNA lineages were found in sympatry. The resultant nuclear mitochondrial discordance suggests the genetic exchangeability among E. canadensis isolates belonging to different lineages. An apparently mosaic parasite fauna that reflects faunal mixing due to natural and anthropogenic disturbance, including introductions and invasion, precludes us from designating each of G6/G7, G8 and G10 into a different species.

Arctic systems in the Quaternary: ecological collision, faunal mosaics and the consequences of a wobbling climate

Climate oscillations and episodic processes interact with evolution, ecology and biogeography to determine the structure and complex mosaic that is the biosphere. Parasites and parasite–host assemblages are key components in a general explanatory paradigm for global biodiversity. We explore faunal assembly in the context of Quaternary time frames of the past 2.6 million years, a period dominated by episodic shifts in climate. Climate drivers cross a continuum from geological to contemporary timescales and serve to determine the structure and distribution of complex biotas. Cycles within cycles are apparent, with drivers that are layered, multifactorial and complex. These cycles influence the dynamics and duration of shifts in environmental structure on varying temporal and spatial scales. An understanding of the dynamics of high-latitude systems, the history of the Beringian nexus (the intermittent land connection linking Eurasia and North America) and downstream patterns of diversity depend on teasing apart the complexity of biotic assembly and persistence. Although climate oscillations have dominated the Quaternary, contemporary dynamics are driven by tipping points and shifting balances emerging from anthropogenic forces that are disrupting ecological structure. Climate change driven by anthropogenic forcing has supplanted a history of episodic variation and is eliminating ecological barriers and constraints on development and distribution for pathogen transmission. A framework to explore interactions of episodic processes on faunal structure and assembly is the Stockholm Paradigm, which appropriately shifts the focus from cospeciation to complexity and contingency in explanations of diversity.

Definitive Hosts of Versteria Tapeworms (Cestoda: Taeniidae) Causing Fatal Infection in North America

We previously reported fatal infection of a captive Bornean orangutan with metacestodes of a novel taeniid tapeworm, Versteria sp. New data implicate mustelids as definitive hosts of these tapeworms in North America. At least 2 parasite genetic lineages circulate in North America, representing separate introductions from Eurasia.

Temporal and spatial mosaics: deep host association and shallow geographic drivers shape genetic structure in a widespread pinworm, Rauschtineria eutamii

Climate and host demographic cycling often shape both parasite genetic diversity and host distributions, processes that transcend a history of strict host-parasite association. We explored host associations and histories based on an evaluation of mitochondrial and nuclear sequences to reveal the underlying history and genetic structure of a pinworm, Rauschtineria eutamii, infecting 10 species of western North American chipmunks (Rodentia:Tamias, subgenus Neotamias). Rauschtineria eutamii contains divergent lineages influenced by the diversity of hosts and variation across the complex topography of western North America. We recovered six reciprocally monophyletic R. eutamii mitochondrial clades, largely supported by nuclear gene trees, exhibiting divergence levels comparable to intraspecific variation reported for other nematodes. Phylogenetic relationships among pinworm clades suggest that R. eutamii colonized an ancestral lineage of western chipmunks and lineages persisted during historical isolation in diverging Neotamias species or species groups. Pinworm diversification, however, is incongruent and asynchronous relative to host diversification. Secondarily, patterns of shallow divergence were shaped by geography through events of episodic colonization reflecting an interaction of taxon pulses and ecological fitting among assemblages in recurrent sympatry. Pinworms occasionally infect geographically proximal host species; however, host switching may be unstable or ephemeral, as there is no signal of host switching in the deeper history of R. eutamii.

Influence of management and biological factors on the parasitic invasions in the wild-spread of blood-sucking nematode Ashworthius sidemi in European bison (Bison bonasus)

The full course of new parasite introductions in wild animals is difficult to accurately trace. We documented and analysed the invasive blood-sucking nematode Ashworthius sidemi (Trichostrongylidae) introduction and spread in European bison (Bison bonasus) from the initial phase of its progression. In the Polish part of the Białowieża Primeval Forest (BPF) the parasite was first found in 2000. From 2002 to 2015, 165 culled bison were investigated. The prevalence and intensity of A. sidemi Schulz, 1933 infection increased over the following years, reaching 100% of investigated bison four years after introduction and a maximal median intensity of 8200 nematodes per animal in the winter of 2008/2009. Afterwards, a significant decline of median infection intensity was observed to the minimum value of 410 nematodes per animal. Between 2011 and 2014 prevalence varied from 89 to 100%. Among the factors analysed, the number of years since introduction, herd size, age and sex proved to significantly influence infection intensity. A higher infection intensity was recorded in sub-adults compared to juveniles and adults. Males had significantly lower infection intensity than females, but this was the case for adults only. The highest infection intensities were recorded in the biggest bison herds, where the winter supplementary feeding of bison is intense. Moreover, the longer the parasite was present in the host population, the more important herd size became as a factor. Our study indicates that it is not solely biological factors that determine the spread of a newly detected parasite in wildlife, but that management practices can also have a strong influence. This is especially important in endangered species under intensive human care as the management practices may pose a threat to the species.

Insights on the host associations and geographic distribution of Hymenolepis folkertsi (Cestoda: Hymenolepididae) among rodents across temperate latitudes of North America

Synoptic data and an understanding of helminth parasite diversity among diverse rodent assemblages across temperate latitudes of North America remain remarkably incomplete. Renewed attention to comprehensive survey and inventory to establish the structure of biodiverse faunas is essential in providing indicators and proxies for identifying the outcomes of accelerating change linked to climate warming and anthropogenic forcing. Subsequent to the description of Hymenolepis folkertsi in the oldfield mouse, Peromyscus polionotus, additional specimens of hymenolepidids were collected or discovered in archived museum repositories from multiple species of deer mice (Peromyscus maniculatus, Peromyscus leucopus), the golden mouse (Ochrotomys nuttalli), chipmunks (Tamias striatus, Tamias amoenus), the 13-lined ground squirrel (Ictidomys tridecemlineatus), and tree squirrels (Sciurus carolinensis, Sciurus niger) from disjunct localities in the USA spanning southern Georgia, Virginia, Pennsylvania, Connecticut, the Upper Peninsula of Michigan, Wisconsin, and central Idaho. Specimens were largely consistent morphologically with the original description of H. folkertsi. Initial DNA sequence data, from a portion of the mitochondrial NADH dehydrogenase subunit 1, demonstrated intraspecific variation among three apparently geographically isolated populations attributed to H. folkertsi (uncorrected genetic distances of 2.7 % (Idaho and Michigan), 2.4 % (Virginia + Pennsylvania and Michigan), and 1.89 % (VA + PA and ID). Geography rather than host association explains the distribution and occurrence of H. folkertsi, and host colonization among deer mice, chipmunks, and other sciurids within regional sites is indicated. Genetic divergence revealed across localities for H. folkertsi suggests historically isolated populations, consistent with extended evolutionary and biogeographic trajectories among hymenolepidids and species of Peromyscus and Tamias in North America. Field inventory, that revealed these parasite populations, substantially alters our understanding of the distribution of diversity and provides insights about the nature of the complex relationships that serve to determine cestode faunas in rodents.

Broadening diversity in the Arostrilepis horrida complex: Arostrilepis kontrimavichusi n. sp. (Cyclophyllidea: Hymenolepididae) in the western red-backed vole Myodes californicus (Merriam) (Cricetidae: Arvicolinae) from temperate latitudes of the Pacific Northwest, North America

Specimens originally identified provisionally as Hymenolepis horrida (Linstow, 1901) [later Arostrilepis horrida (Linstow, 1901)] in Myodes californicus (Merriam) from near the Pacific coastal zone of southern Oregon are revised. Specimens in western red-backed voles represent an undescribed species of Arostrilepis Mas Coma & Tenora, 1997, contributing to recognition and resolution of a broadening complex encompassing cryptic diversity for these hymenolepidid tapeworms distributed across the Holarctic region. Consistent with recent studies defining diversity in the genus, the form, dimensions, and spination (pattern, shape and size) of the cirrus are diagnostic. Among 12 nominal congeners, specimens of A. kontrimavichusi n. sp. are further distinguished by the relative position and length of the cirrus-sac, arrangement of the testes and relative size of the external seminal vesicle and seminal receptacle. Specimens from Oregon voles represent the fifth endemic hymenolepidid in this genus from the Nearctic. Host range for the North American assemblage of species includes Cricetidae (Arvicolinae and Neotominae), Heteromyidae, Geomyidae, and rarely Sciuridae.

First record of the Holarctic least shrew (Sorex minutissimus) and associated helminths from Canada: new light on northern Pleistocene refugia

We report the first Canadian record of the Holarctic least shrew (Sorex minutissimus Zimmermann, 1780) and associated helminth worms, collected along the Dempster Highway in central Yukon in 2014. We identify the specimen based on morphological characters, characterize the habitat, report other mammals and helminth species associated with this specimen, and use mitochondrial DNA sequences to place the specimen within a phylogenetic context and address Pleistocene refugial hypotheses. Although long considered an Eurasian endemic, the diminutive least shrew was first reported from Alaska in 1994. Our new record for Canada indicates that the species may occur at least as far east as the MacKenzie River and DNA variation suggests this species persisted only in the Beringian refugium in North America during the Last Glacial Maximum. The discovery of a new mammal and associated parasites for Canada points to the urgent need for more detailed information on high-latitude biotas in North America, data that are best obtained through museum-based field surveys, particularly for small, cryptic species.

Revision of widespread red squirrels (genus: Tamiasciurus) highlights the complexity of speciation within North American forests

Integration of molecular methods, ecological modeling, and statistical hypothesis testing are increasing our understanding of differentiation within species and phylogenetic relationships among species by revealing environmental connections to evolutionary processes. Within mammals, novel diversity is being discovered and characterized as more complete geographic sampling is coupled with newer multi-disciplinary approaches. North American red squirrels exemplify a forest obligate genus whose species are monitored as indicators of forest ecosystem condition, yet phylogenetic relationships reflecting evolutionary history within this genus remain tentative. Through testing of competing systematic and niche-based divergence hypotheses, we recognize three species, Tamiasciurus douglasii, T. hudsonicus, and T. fremonti. Our data provide evidence of regional differences in evolutionary dynamics and continental gradients of complexity that are important both for future management and for investigating multiple pathways that can lead to the formation of new species.

Reappraisal of Hydatigera taeniaeformis (Batsch, 1786) (Cestoda: Taeniidae) sensu lato with description of Hydatigera kamiyai n. sp

The common cat tapeworm Hydatigera taeniaeformis is a complex of three morphologically cryptic entities, which can be differentiated genetically. To clarify the biogeography and the host spectrum of the cryptic lineages, 150 specimens of H. taeniaeformis in various definitive and intermediate hosts from Eurasia, Africa and Australia were identified with DNA barcoding using partial mitochondrial cytochrome c oxidase subunit 1 gene sequences and compared with previously published data. Additional phylogenetic analyses of selected isolates were performed using nuclear DNA and mitochondrial genome sequences. Based on molecular data and morphological analysis, Hydatigera kamiyai n. sp. Iwaki is proposed for a cryptic lineage, which is predominantly northern Eurasian and uses mainly arvicoline rodents (voles) and mice of the genus Apodemus as intermediate hosts. Hydatigera taeniaeformis sensu stricto (s.s.) is restricted to murine rodents (rats and mice) as intermediate hosts. It probably originates from Asia but has spread worldwide. Despite remarkable genetic divergence between H. taeniaeformis s.s. and H. kamiyai, interspecific morphological differences are evident only in dimensions of rostellar hooks. The third cryptic lineage is closely related to H. kamiyai, but its taxonomic status remains unresolved due to limited morphological, molecular, biogeographical and ecological data. This Hydatigera sp. is confined to the Mediterranean and its intermediate hosts are unknown. Further studies are needed to classify Hydatigera sp. either as a distinct species or a variant of H. kamiyai. According to previously published limited data, all three entities occur in the Americas, probably due to human-mediated introductions.

Phylogenomic and biogeographic reconstruction of the Trichinella complex

Trichinellosis is a globally important food-borne parasitic disease of humans caused by roundworms of the Trichinella complex. Extensive biological diversity is reflected in substantial ecological and genetic variability within and among Trichinella taxa, and major controversy surrounds the systematics of this complex. Here we report the sequencing and assembly of 16 draft genomes representing all 12 recognized Trichinella species and genotypes, define protein-coding gene sets and assess genetic differences among these taxa. Using thousands of shared single-copy orthologous gene sequences, we fully reconstruct, for the first time, a phylogeny and biogeography for the Trichinella complex, and show that encapsulated and non-encapsulated Trichinella taxa diverged from their most recent common ancestor ∼21 million years ago (mya), with taxon diversifications commencing ∼10-7 mya.