Non-native Host Research Articles

A coupled in vitro/in vivo approach for engineering a heterologous type III PKS to enhance polyketide biosynthesis in Saccharomyces cerevisiae.

Polyketides are attractive compounds for uses ranging from biorenewable chemical precursors to high-value therapeutics. In many cases, synthesis in a heterologous host is required to produce these compounds in industrially relevant quantities. The type III polyketide synthase 2-pyrone synthase (2-PS) from Gerbera hybrida was used for the production of triacetic acid lactone (TAL) in Saccharomyces cerevisiae. Initial in vitro characterization of 2-PS led to the identification of active site variants with improved kinetic properties relative to wildtype. Further in vivo evaluation in S. cerevisiae suggested certain 2-PS mutations altered enzyme stability during fermentation. In vivo experiments also revealed beneficial cysteine to serine mutations that were not initially explored due to their distance from the active site of 2-PS, leading to the design of additional 2-PS enzymes. While these variants showed varying catalytic efficiencies in vitro, they exhibited up to 2.5-fold increases in TAL production when expressed in S. cerevisiae. Coupling of the 2-PS variant [C35S,C372S] to an engineered S. cerevisiae strain led to over 10 g/L TAL at 38% of theoretical yield following fed-batch fermentation, the highest reported to date. Our studies demonstrate the success of a coupled in vitro/in vivo approach to engineering enzymes and provide insight on cysteine-rich enzymes and design principles toward their use in non-native microbial hosts.

Symbiont interactions with non-native hosts limit the formation of new symbioses

BackgroundFacultative symbionts are common in eukaryotes and can provide their hosts with significant fitness benefits. Despite the advantage of carrying these microbes, they are typically only found in a fraction of the individuals within a population and are often non-randomly distributed among host populations. It is currently unclear why facultative symbionts are only found in certain host individuals and populations. Here we provide evidence for a mechanism to help explain this phenomenon: that when symbionts interact with non-native host genotypes it can limit the horizontal transfer of symbionts to particular host lineages and populations of related hosts.ResultsUsing reciprocal transfections of the facultative symbiont Hamiltonella defensa into different pea aphid clones, we demonstrate that particular symbiont strains can cause high host mortality and inhibit offspring production when injected into aphid clones other than their native host lineage. However, once established, the symbiont’s ability to protect against parasitoids was not influenced by its origin. We then demonstrate that H. defensa is also more likely to establish a symbiotic relationship with aphid clones from a plant-adapted population (biotype) that typically carry H. defensa in nature, compared to clones from a biotype that does not normally carry this symbiont.ConclusionsThese results provide evidence that certain aphid lineages and populations of related hosts are predisposed to establishing a symbiotic relationship with H. defensa. Our results demonstrate that host-symbiont genotype interactions represent a potential barrier to horizontal transmission that can limit the spread of symbionts, and adaptive traits they carry, to certain host lineages.

The unspecificity of the relationships between the invasive Pennisetum setaceum and mycorrhizal fungi may provide advantages during its establishment at semiarid Mediterranean sites

The involvement of mutualistic plant-fungal interactions in invasion processes, especially in some climatic regions including semiarid areas, has not been sufficiently investigated. We compared the arbuscular mycorrhizal fungi (AMF) communities hosted by the invasive plant Pennisetum setaceum with those from the co-occurring native Hyparrhenia hirta at five Mediterranean semiarid locations with different edaphic characteristics. Illumina technology was used to investigate the AMF communities in the roots. The subsequent multivariate analysis showed that native and non-native host plants shared a similar AMF community, whereas the invaded locations differed in AMF communities harbored in the plant roots. The indicator species analysis revealed the absence of indicator virtual taxa for the fungal communities of the roots of native or invasive plants. In contrast, different numbers of indicator species were recorded in different sampling locations. According to the canonical correspondence analysis, the variability in the AMF communities between sampling sites was related to changes in soil total carbon, electrical conductivity, respiration, and protease and urease activities. These findings reveal the unspecificity of P. setaceum in relation to its association with the AMF community encountered in the invaded locations, which could have facilitated its successful establishment and spread.

Biological conversion of methane to chemicals and fuels: technical challenges and issues

Methane is a promising next-generation carbon feedstock for industrial biotechnology due to its low price and huge availability. Biological conversion of methane to valuable products can mitigate methane-induced global warming as greenhouse gas. There have been challenges for the conversion of methane into various chemicals and fuels using engineered non-native hosts with synthetic methanotrophy or methanotrophs with the reconstruction of synthetic pathways for target products. Herein, we analyze the technical challenges and issues of potent methane bioconversion technology. Pros and cons of metabolic engineering of methanotrophs for methane bioconversion, and perspectives on the bioconversion of methane to chemicals and liquid fuels are discussed.

Assessing the current and future biological control potential of Trichogramma ostriniae on its hosts Ostrinia furnacalis and Ostrinia nubilalis.

Understanding interactions between biocontrol agents and their pest hosts under climate change should assist implementation of biocontrol strategies, by identifying appropriate biocontrol agents for release or determining the optimal timing of releases. Species distribution models (SDMs) were applied to evaluate the distributions of Trichogramma ostriniae and its native host, Ostrinia furnacalis, in southeastern Asia, and a non-native host, Ostrinia nubilalis, in a novel range, North America, using MAXENT and CLIMEX modelling approaches. The models led to similar predictions about the expected distribution of the two species in Asia, and emphasized likely mismatches between host and natural enemy. Trichogramma ostriniae was predicted to occur in the summer corn region of China, with distribution limits linked to its sensitivity to cold, seasonality of radiation and precipitation. The modelled Ostrinia nubilalis distribution overlapped with the main corn production areas of the northeastern USA and Canada; temporary/seasonal suitable habitat was also predicted across the southeastern USA. Climate change scenarios are predicted to favour T. ostriniae over its hosts in northeastern China and North America. The modelling approaches used here proved useful for assessing environmental factors linked to an egg parasitoid and its lepidopteran hosts and identifying areas potentially suitable for inundative releases. © 2017 Society of Chemical Industry.

Production of (2R, 3R)-2,3-butanediol using engineered Pichia pastoris: strain construction, characterization and fermentation

Background2,3-butanediol (2,3-BD) is a bulk platform chemical with various potential applications such as aviation fuel. 2,3-BD has three optical isomers: (2R, 3R)-, (2S, 3S)- and meso-2,3-BD. Optically pure 2,3-BD is a crucial precursor for the chiral synthesis and it can also be used as anti-freeze agent due to its low freezing point. 2,3-BD has been produced in both native and non-native hosts. Several pathogenic bacteria were reported to produce 2,3-BD in mixture of its optical isomers including Klebsiella pneumoniae and Klebsiella oxytoca. Engineered hosts based on episomal plasmid expression such as Escherichia coli, Saccharomyces cerevisiae and Bacillus subtilis are not ideal for industrial fermentation due to plasmid instability.ResultsPichia pastoris is generally regarded as safe and a well-established host for high-level heterologous protein production. To produce pure (2R, 3R)-2,3-BD enantiomer, we developed a P. pastoris strain by introducing a synthetic pathway. The alsS and alsD genes from B. subtilis were codon-optimized and synthesized. The BDH1 gene from S. cerevisiae was cloned. These three pathway genes were integrated into the genome of P. pastoris and expressed under the control of GAP promoter. Production of (2R, 3R)-2,3-BD was achieved using glucose as feedstock. The optical purity of (2R, 3R)-2,3-BD was more than 99%. The titer of (2R, 3R)-2,3-BD reached 12 g/L with 40 g/L glucose as carbon source in shake flask fermentation. The fermentation conditions including pH, agitation speeds and aeration rates were optimized in batch cultivations. The highest titer of (2R, 3R)-2,3-BD achieved in fed-batch fermentation using YPD media was 45 g/L. The titer of 2,3-BD was enhanced to 74.5 g/L through statistical medium optimization.ConclusionsThe potential of engineering P. pastoris into a microbial cell factory for biofuel production was evaluated in this work using (2R, 3R)-2,3-BD as an example. Engineered P. pastoris could be a promising workhorse for the production of optically pure (2R, 3R)-2,3-BD.

Guppies (Poecilia reticulata) introducing an alien parasite, Camallanus cotti (Nematoda: Camallanidae) to Africa, the first report.

Introduced alien fish species and their associated parasites may result in a serious threat to indigenous biodiversity. Furthermore, this may have negative impacts on cultured fish as well as on native parasitic fauna. In the present study, the invasive Asian nematode, Camallanus cotti Fujita, 1927 (Nematoda: Camallanidae), is reported from the guppy (Poecilia reticulata) for the first time in Africa. This parasite is assumed to be introduced into Africa along with the introduction of exotic poeciliid fishes, which are known to be the most common hosts of C. cotti in ornamental fish industry worldwide.The presence of this parasite in both aquarium-cultured fish as well as fish from natural waterbodies is evidence of the introduction of the alien organisms due to insufficient prophylactic veterinary control during transfer of non-native hosts between countries and the spread of them by the anthropogenic introduction to natural systems.

Native or nonnative host plants: What is better for a specialist moth?

The enemy release hypothesis (ERH) predicts that the lack of natural enemies, such as herbivores, contributes to the success of nonnative plants as colonizers. Larvae of the Neotropical specialist moth Utetheisa ornatrix (Erebidae: Arctiinae) can feed on unripe seeds and leaves of both native and nonnative Crotalaria species (Fabaceae). Despite some species being able to eat nonnative plants, such behavior can impair the herbivore, as they are not adapted to the alien plant, and still contribute to the success of the nonnative species via enemy release. We tested the performance of the moth from hatching to adulthood fed on two native (C. micans and C. paulina) and two nonnative (C. pallida, C. juncea) host plants. Utetheisa ornatrix performed better (lower development time, heavier pupae and more eggs) on the native host plants than in the nonnative. However, larva performance in nonnative C. pallida was similar to that in the native host plants. Using the larval weight 7 days after hatching from the eggs as a proxy for performance in twelve Crotalaria species (five Neotropical natives, four nonnatives from Afrotropical region, and three nonnatives from India), we found similar results. Crotalaria nutritional compounds, the defensive pyrrolizidine alkaloids and Crotalaria phylogeny did not explain moth performance. Our results give some support to the ERH. The good moth performance in nonnative C. pallida may be related to its high availability as host plant for U. ornatrix, and its longer time since their introduction in Neotropics which would provide opportunity for the moth to adapt.

Diversity of tree-infecting Botryosphaeriales on native and non-native trees in South Africa and Namibia

The Botryosphaeriales includes serious plant pathogens with a broad host and geographic distribution globally. In South Africa and Namibia, these fungi include important pathogens of native and non-native woody plants, and have consequently been studied extensively. Here we synthesize the information from the previous studies, particularly in the last decade, that report 62 species in the Botryosphaeriales from 66 hosts across South Africa and Namibia. Of these, 52 species have been reported from native hosts, 17 are from non-native hosts and twelve of these species occur on both native and non-native trees in the region. Much of the diversity of the Botryosphaeriales can be ascribed to native species that have fairly limited host and geographic ranges. Neofusicoccum parvum is amongst the most common species on both native and non-native hosts and it is thought to be native to the region. In contrast, Botryosphaeria dothidea, which is certainly an introduced species, is also widespread, and is very common on both native and non-native plants. Overall this synthesis underscores the growing understanding of the diversity of an important group of tree pathogens, their apparently common global spread as latent agents of disease, as well as their apparently common movement between commercial and native ecosystems.

Heterologous Expression of the Clostridium carboxidivorans CO Dehydrogenase Alone or Together with the Acetyl Coenzyme A Synthase Enables both Reduction of CO2 and Oxidation of CO by Clostridium acetobutylicum.

With recent advances in synthetic biology, CO2 could be utilized as a carbon feedstock by native or engineered organisms, assuming the availability of electrons. Two key enzymes used in autotrophic CO2 fixation are the CO dehydrogenase (CODH) and acetyl coenzyme A (acetyl-CoA) synthase (ACS), which form a bifunctional heterotetrameric complex. The CODH/ACS complex can reversibly catalyze CO2 to CO, effectively enabling a biological water-gas shift reaction at ambient temperatures and pressures. The CODH/ACS complex is part of the Wood-Ljungdahl pathway (WLP) used by acetogens to fix CO2, and it has been well characterized in native hosts. So far, only a few recombinant CODH/ACS complexes have been expressed in heterologous hosts, none of which demonstrated in vivo CO2 reduction. Here, functional expression of the Clostridium carboxidivorans CODH/ACS complex is demonstrated in the solventogen Clostridium acetobutylicum, which was engineered to express CODH alone or together with the ACS. Both strains exhibited CO2 reduction and CO oxidation activities. The CODH reactions were interrogated using isotopic labeling, thus verifying that CO was a direct product of CO2 reduction, and vice versa. CODH apparently uses a native C. acetobutylicum ferredoxin as an electron carrier for CO2 reduction. Heterologous CODH activity depended on actively growing cells and required the addition of nickel, which is inserted into CODH without the need to express the native Ni insertase protein. Increasing CO concentrations in the gas phase inhibited CODH activity and altered the metabolite profile of the CODH-expressing cells. This work provides the foundation for engineering a complete and functional WLP in nonnative host organisms.IMPORTANCE Functional expression of CO dehydrogenase (CODH) from Clostridium carboxidivorans was demonstrated in C. acetobutylicum, which is natively incapable of CO2 fixation. The expression of CODH, alone or together with the C. carboxidivorans acetyl-CoA synthase (ACS), enabled C. acetobutylicum to catalyze both CO2 reduction and CO oxidation. Importantly, CODH exhibited activity in both the presence and absence of ACS. 13C-tracer studies confirmed that the engineered C. acetobutylicum strains can reduce CO2 to CO and oxidize CO during growth on glucose.

Complete Biosynthesis of Anthocyanins Using E. coli Polycultures.

ABSTRACTFermentation-based chemical production strategies provide a feasible route for the rapid, safe, and sustainable production of a wide variety of important chemical products, ranging from fuels to pharmaceuticals. These strategies have yet to find wide industrial utilization due to their inability to economically compete with traditional extraction and chemical production methods. Here, we engineer for the first time the complex microbial biosynthesis of an anthocyanin plant natural product, starting from sugar. This was accomplished through the development of a synthetic, 4-strain Escherichia coli polyculture collectively expressing 15 exogenous or modified pathway enzymes from diverse plants and other microbes. This synthetic consortium-based approach enables the functional expression and connection of lengthy pathways while effectively managing the accompanying metabolic burden. The de novo production of specific anthocyanin molecules, such as calistephin, has been an elusive metabolic engineering target for over a decade. The utilization of our polyculture strategy affords milligram-per-liter production titers. This study also lays the groundwork for significant advances in strain and process design toward the development of cost-competitive biochemical production hosts through nontraditional methodologies.

Reconstitution of a minimal machinery capable of assembling periplasmic type IV pili

Type IV pili (Tfp), which are key virulence factors in many bacterial pathogens, define a large group of multipurpose filamentous nanomachines widespread in Bacteria and Archaea. Tfp biogenesis is a complex multistep process, which relies on macromolecular assemblies composed of 15 conserved proteins in model gram-negative species. To improve our limited understanding of the molecular mechanisms of filament assembly, we have used a synthetic biology approach to reconstitute, in a nonnative heterologous host, a minimal machinery capable of building Tfp. Here we show that eight synthetic genes are sufficient to promote filament assembly and that the corresponding proteins form a macromolecular complex at the cytoplasmic membrane, which we have purified and characterized biochemically. Our results contribute to a better mechanistic understanding of the assembly of remarkable dynamic filaments nearly ubiquitous in prokaryotes.

Parasites, pathogens and commensals in the \u201clow-impact\u201d non-native amphipod host Gammarus roeselii

BackgroundWhilst vastly understudied, pathogens of non-native species (NNS) are increasingly recognised as important threats to native wildlife. This study builds upon recent recommendations for improved screening for pathogens in NNS by focusing on populations of Gammarus roeselii in Chojna, north-western Poland. At this location, and in other parts of continental Europe, G. roeselii is considered a well-established and relatively ‘low-impact’ invader, with little understanding about its underlying pathogen profile and even less on potential spill-over of these pathogens to native species.ResultsUsing a combination of histological, ultrastructural and phylogenetic approaches, we define a pathogen profile for non-native populations of G. roeselii in Poland. This profile comprised acanthocephalans (Polymorphus minutus Goese, 1782 and Pomphorhynchus sp.), digenean trematodes, commensal rotifers, commensal and parasitic ciliated protists, gregarines, microsporidia, a putative rickettsia-like organism, filamentous bacteria and two viral pathogens, the majority of which are previously unknown to science. To demonstrate potential for such pathogenic risks to be characterised from a taxonomic perspective, one of the pathogens, a novel microsporidian, is described based upon its pathology, developmental cycle and SSU rRNA gene phylogeny. The novel microsporidian Cucumispora roeselii n. sp. displayed closest morphological and phylogenetic similarity to two previously described taxa, Cucumispora dikerogammari (Ovcharenko & Kurandina, 1987), and Cucumispora ornata Bojko, Dunn, Stebbing, Ross, Kerr & Stentiford, 2015.ConclusionsIn addition to our discovery extending the host range for the genus Cucumispora Ovcharenko, Bacela, Wilkinson, Ironside, Rigaud & Wattier, 2010 outside of the amphipod host genus Dikerogammarus Stebbing, we reveal significant potential for the co-transfer of (previously unknown) pathogens alongside this host when invading novel locations. This study highlights the importance of pre-invasion screening of low-impact NNS and, provides a means to document and potentially mitigate the additional risks posed by previously unknown pathogens.

Association of Potato Psyllid (Bactericera cockerelli; Hemiptera: Triozidae) with Lycium spp. (Solanaceae) in Potato Growing Regions of Washington, Idaho, and Oregon

Potato psyllid, Bactericera cockerelli (Sulc), causes economic damage to potato crops throughout the major potato growing regions of western North America. When cultivated crops are not available, potato psyllid often occurs on non-crop hosts. In the southern U.S. and northern Mexico, native species of Lycium (Solanaceae) are important non-crop hosts for the psyllid. We determined whether Old World species of Lycium now widespread in the Pacific Northwest are reservoirs of potato psyllid in this growing region. We examined Lycium spp. across a wide geographic region in Washington, Oregon, and Idaho at irregular intervals during three growing seasons. Potato psyllids were present at all locations. To determine whether Lycium is also a host during intervals of the year in which the potato crop is not available, we monitored a subset of these sites over the entire year. Six sites were monitored at 1- to 3-week intervals from June 2014 to June 2016. Psyllids were present on Lycium throughout the year at all sites, including during winter, indicating that Lycium is also a host when the potato crop is seasonally not available. Psyllid populations included a mixture of Northwestern and Western haplotypes. We observed well-defined spring and fall peaks in adult numbers, with peaks separated by long intervals in which psyllid numbers were very low. Seasonal patterns in psyllid numbers on these non-native Lycium hosts were very similar to what has been observed on native Lycium in the desert southwest region of the U.S. Our findings demonstrate that potato psyllid associates with Lycium across a broad geographic region within the Pacific Northwest. These results will assist in predicting sources of potato psyllid colonizing potatoes in this important growing region.

Initial Response by a Native Beetle, Chrysochus auratus (Coleoptera: Chrysomelidae), to a Novel Introduced Host-Plant, Vincetoxicum rossicum (Gentianales: Apocynaceae).

Native insects can form novel associations with introduced invasive plants and use them as a food source. The recent introduction into eastern North America of a nonnative European vine, Vincetoxicum rossicum (Kleopow) Barbar., allows us to examine the initial response of a native chrysomelid beetle, Chrysochus auratus F., that feeds on native plants in the same family as V. rossicum (Apocynaceae). We tested C. auratus on V. rossicum and closely related or co-occurring native plants (Apocynum spp., Asclepias spp., and Solidago canadensis L.) using all life stages of the beetle in lab, garden, and field experiments. Experiments measured feeding (presence or absence and amount), survival, oviposition, and whether previous exposure to V. rossicum in the lab or field affected adult beetle feeding. Beetles fed significantly less on V. rossicum than on native Apocynum hosts. Adult beetles engaged in exploratory feeding on leaves of V. rossicum and survived up to 10 d. Females oviposited on V. rossicum, eggs hatched, and larvae fed initially on the roots; however, no larvae survived beyond second instar. Beetles collected from Apocynum cannabinum L. field sites intermixed with V. rossicum were less likely to feed on this novel nonnative host than those collected from colonies further from and less likely to be exposed to V. rossicum (>5 km). Our experimental work indicates that V. rossicum may act as an oviposition sink for C. auratus and that this native beetle has not adapted to survive on this recently introduced novel host plant.

Impacts of crustacean invasions on parasite dynamics in aquatic ecosystems: A plea for parasite-focused studies.

While there is considerable interest in, and good evidence for, the role that parasites play in biological invasions, the potential parallel effects of species introduction on parasite dynamics have clearly received less attention. Indeed, much effort has been focused on how parasites can facilitate or limit invasions, and positively or negatively impact native host species and recipient communities. Contrastingly, the potential consequences of biological invasions for the diversity and dynamics of both native and introduced parasites have been and are still mainly overlooked, although successful invasion by non-native host species may have large, contrasting and unpredictable effects on parasites. This review looks at the links between biological invasions and pathogens, and particularly at crustacean invasions in aquatic ecosystems and their potential effects on native and invasive parasites, and discusses what often remains unknown even from well-documented systems. Aquatic crustaceans are hosts to many parasites and are often invasive. Published studies show that crustacean invasion can have highly contrasting effects on parasite dynamics, even when invasive host and parasite species are phylogenetically close to their native counterparts. These effects seem to be dependent on multiple factors such as host suitability, parasite life-cycle or host-specific resistance to parasitic manipulation. Furthermore, introduced hosts can have drastically contrasting effects on parasite standing crop and transmission, two parameters that should be independently assessed before drawing any conclusion on the potential effects of novel hosts on parasites and the key processes influencing disease dynamics following biological invasions. I conclude by calling for greater recognition of biological invasions’ effects on parasite dynamics, more parasite-focused studies and suggest some potential ways to assess these effects.

Strains of Photorhabdus spp. associated with polish Heterorhabditis isolates: their molecular and phenotypic characterization and symbiont exchange.

The relationships between six bacterial symbionts of the entomopathogenic nematodes Heterorhabditis bacteriophora and Heterorhabditis megidis from Poland to species and subspecies of the genus Photorhabdus were evaluated. This study was based on phylogenetic analysis of sequence data of five genes: 16S rRNA, gyrB, recA, gltX, and dnaN. The bacteria were also characterized phenotypically by biochemical and physiological tests. Our results have revealed that the Photorhabdus strains isolated from H. megidis belong to P. temperata, subsp. temperata and subsp. cinerea. Isolates from H. bacteriophora represent P. luminescens subs. kayaii and P. temperata subs. cinerea. This study for the first time provides evidence for H. bacteriophora and P. temperata subsp. cinerea symbiotic association. In addition, we tested whether the microsymbionts of the Polish H. bacteriophora and H. megidis isolates support the development of non-native nematode host population and colonization of their infective juveniles. It has been shown that the studied Photorhabdus strains can readily swap their nematode host, both at intra- and interspecies level. It supports the hypothesis of different symbiotic associations in the Heterorhabditis-Photorhabdus lineage.

Understanding Primate Herpesviruses.

Viruses related to the herpes simplex viruses of humans are present in all nonhuman primate (NHP) species tested and cross species transmission has been documented. The herpesvirus present in macaques, Herpes B virus (BV) rarely causes disease in its natural macaque host. However, when transmitted to a nonnative host, BV has occasionally caused severe and even fatal disease if not treated immediately. Here we present a comprehensive review of the taxonomy, molecular biology, physiology, epidemiology, diagnosis and treatment of BV. We also summarizes what is known about related herpesviruses of other NHP species and the zoonotic potential of these viruses.

Metazoan parasite communities: support for the biological invasion of Barbus barbus and its hybridization with the endemic Barbus meridionalis.

BackgroundRecently, human intervention enabled the introduction of Barbus barbus from the Rhône River basin into the Barbus meridionalis habitats of the Argens River. After an introduction event, parasite loss and lower infection can be expected in non-native hosts in contrast to native species. Still, native species might be endangered by hybridization with the incomer and the introduction of novel parasite species. In our study, we aimed to examine metazoan parasite communities in Barbus spp. populations in France, with a special emphasis on the potential threat posed by the introduction of novel parasite species by invasive B. barbus to local B. meridionalis. MethodsMetazoan parasite communities were examined in B. barbus, B. meridionalis and their hybrids in three river basins in France. Microsatellites were used for the species identification of individual fish. Parasite abundance, prevalence, and species richness were compared. Effects of different factors on parasite infection levels and species richness were tested using GLM.ResultsMetazoan parasites followed the expansion range of B. barbus and confirmed its introduction into the Argens River. Here, the significantly lower parasite number and lower levels of infection found in B. barbus in contrast to B. barbus from the Rhône River supports the enemy release hypothesis. Barbus barbus × B. meridionalis hybridization in the Argens River basin was confirmed using both microsatellites and metazoan parasites, as hybrids were infected by parasites of both parental taxa. Trend towards higher parasite diversity in hybrids when compared to parental taxa, and similarity between parasite communities from the Barbus hybrid zone suggest that hybrids might represent “bridges” for parasite infection between B. barbus and B. meridionalis. Risk of parasite transmission from less parasitized B. barbus to more parasitized B. meridionalis indicated from our study in the Argens River might be enhanced in time as higher infection levels in B. barbus from the Rhône River were revealed. Hybrid susceptibility to metazoan parasites varied among the populations and is probably driven by host-parasite interactions and environmental forces.ConclusionsScientific attention should be paid to the threatened status of the endemic B. meridionalis, which is endangered by hybridization with the invasive B. barbus, i.e. by genetic introgression and parasite transmission.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1867-9) contains supplementary material, which is available to authorized users.

Uncorrelated mistletoe infection patterns and mating success with local host specialization in Psittacanthus calyculatus (Loranthaceae)

Mistletoe infection between conspecific and interspecific hosts can be restricted by seed dispersal, host-mistletoe compatibility and abiotic factors, yet no studies have linked mistletoe infection patterns and pollination together for understanding mistletoe distribution at a local scale. Psittacanthus calyculatus (Loranthaceae) is a hemiparasitic plant with a broad host range across its geographic distribution. The potential for local host adaptation has been shown using cross-inoculation experiments, in which plants of mistletoe seeds collected from a given host are more likely to survive when they are inoculated on conspecific host trees compared with those inoculated on other host provenances. Here we evaluate host adaptation by describing the local patterns of infection (prevalence and intensity) of P. calyculatus mistletoes on three native host tree species (Alnus acuminata, Quercus crassipes, Salix bonplandiana) and one introduced species (Populus alba) and carried out cross-pollination experiments to examine how pollination affects infection patterns of different host species. Mistletoe infection prevalence (proportion of infection) and infection intensity (mean number of mistletoes per tree) were in general disproportional with respect to the availability of native host tree species but higher to that of non-native host tree species. Cross-pollination experiments showed higher mating success on the native host tree species, suggesting higher local adaptation to specially Q. crassipes. The observed spatial distribution of host tree species and mistletoe infection along with the non-random mating could contribute to local genetic structuring of mistletoe populations.