Anti-pathogen protection versus survival costs mediated by an ectosymbiont in an ant host

The fitness effects of symbionts on their hosts can be context-dependent, with usually benign symbionts causing detrimental effects when their hosts are stressed, or typically parasitic symbionts providing protection towards their hosts (e.g. against pathogen infection). Here, we studied the novel association between the invasive garden ant Lasius neglectus and its fungal ectosymbiont Laboulbenia formicarum for potential costs and benefits. We tested ants with different Laboulbenia levels for their survival and immunity under resource limitation and exposure to the obligate killing entomopathogen Metarhizium brunneum. While survival of L. neglectus workers under starvation was significantly decreased with increasing Laboulbenia levels, host survival under Metarhizium exposure increased with higher levels of the ectosymbiont, suggesting a symbiont-mediated anti-pathogen protection, which seems to be driven mechanistically by both improved sanitary behaviours and an upregulated immune system. Ants with high Laboulbenia levels showed significantly longer self-grooming and elevated expression of immune genes relevant for wound repair and antifungal responses (β-1,3-glucan binding protein, Prophenoloxidase), compared with ants carrying low Laboulbenia levels. This suggests that the ectosymbiont Laboulbenia formicarum weakens its ant host by either direct resource exploitation or the costs of an upregulated behavioural and immunological response, which, however, provides a prophylactic protection upon later exposure to pathogens.     

HORMESIS RESULTS IN TRADE‐OFFS WITH IMMUNITY

Many have argued that we may be able to extend life and improve human health through hormesis, the beneficial effects of low‐level toxins and other stressors. But, studies of hormesis in model systems have not yet established whether stress‐induced benefits are cost free, artifacts of inbreeding, or come with deleterious side effects. Here, we provide evidence that hormesis results in trade‐offs with immunity. We find that a single topical dose of dead spores of the entomopathogenic fungus, Metarhizium robertsii, increases the longevity of the fruit fly, Drosophila melanogaster, without significant decreases in fecundity. We find that hormetic benefits of pathogen challenge are greater in lines that lack key components of antifungal immunity (Dif and Turandot M). And, in outbred fly lines, we find that topical pathogen challenge enhances both survival and fecundity, but reduces ability to fight off live infections. The results provide evidence that hormesis is manifested by stress‐induced trade‐offs with immunity, not cost‐free benefits or artifacts of inbreeding. Our findings illuminate mechanisms underlying pathogen‐induced life‐history trade‐offs, and indicate that reduced immune function may be an ironic side effect of the “elixirs of life.”     

Autophagy plays an important role in protecting Pacific oysters from OsHV-1 and Vibrio aestuarianus infections

Recent mass mortality outbreaks around the world in Pacific oysters, Crassostrea gigas, have seriously affected the aquaculture economy. Although the causes for these mortality outbreaks appear complex, infectious agents are involved. Two pathogens are associated with mass mortality outbreaks, the virus ostreid herpesvirus 1 (OsHV-1) and the bacterium Vibrio aestuarianus. Here we describe the interactions between these 2 pathogens and autophagy, a conserved intracellular pathway playing a key role in innate immunity. We show for the first time that autophagy pathway is present and functional in Pacific oysters and plays an important role to protect animals from infections. This study contributes to better understand the innate immune system of Pacific oysters.     

Effects of Plasmodium gallinaceum on hemolymph physiology of Aedes aegypti during parasite development

Insect disease vectors show diminished fecundity when infected with Plasmodium. This phenomenon has already been demonstrated in laboratory models such as Aedes aegypti, Anopheles gambiae and Anopheles stephensi. This study demonstrates several changes in physiological processes of A. aegypti occurring upon infection with Plasmodium gallinaceum, such as reduced ecdysteroid levels in hemolymph as well as altered expression patterns for genes involved in vitellogenesis, lipid transport and immune response. Furthermore, we could show that P. gallinaceum infected A. aegypti presented a reduction in reproductive fitness, accompanied by an activated innate immune response and increase in lipophorin expression, with the latter possibly representing a nutritional resource for Plasmodium sporozoites.     

The Arabidopsis LECTIN RECEPTOR KINASE-VI.2 is a functional protein kinase and is dispensable for basal resistance to Botrytis cinerea

Sensing of microbial pathogens by pathogen-associated molecular patterns (PAMPs) through pattern recognition receptors (PRRs) elicits a defense program known as PAMP-triggered immunity (PTI). Recently, we have shown that the Arabidopsis thaliana L-TYPE LECTIN RECEPTOR KINASE-VI.2 (LecRK-VI.2) positively regulates bacterial PTI. In this report, we suggest by in silico analysis that the kinase domain of LecRK-VI.2 is functional. LecRK-VI.2 also demonstrated auto-phosphorylation activity in vitro in the presence of divalent metal cations indicating that LecRK-VI.2 has the ability to auto-phosphorylate. We further investigate the role of LecRK-VI.2 in Arabidopsis resistance to the necrotrophic fungal pathogen Botrytis cinerea. Disruption of LecRK-VI.2 did not affect Arabidopsis resistance to B. cinerea. Accordingly, wild-type upregulation levels of PTI-responsive WRKY53, FRK1, NHL10, CYP81F2 and CBP60 g after treatment with the fungal PAMP chitin were observed in lecrk-VI.2-1. These data provide evidences that the kinase domain of LecRK-VI.2 is active and show that LecRK-VI.2 is not critical for resistance to the fungal pathogen B. cinerea.     

Female and male genetic contributions to post-mating immune defence in female Drosophila melanogaster

Post-mating reduction in immune defence is common in female insects, and a trade-off between mating and immunity could affect the evolution of immunity. In this work, we tested the capacity of virgin and mated female Drosophila melanogaster to defend against infection by four bacterial pathogens. We found that female D. melanogaster suffer post-mating immunosuppression in a pathogen-dependent manner. The effect of mating was seen after infection with two bacterial pathogens (Providencia rettgeri and Providencia alcalifaciens), though not after infection with two other bacteria (Enterococcus faecalis and Pseudomonas aeruginosa). We then asked whether the evolution of post-mating immunosuppression is primarily a ‘female’ or ‘male’ trait by assaying for genetic variation among females for the degree of post-mating immune suppression they experience and among males for the level of post-mating immunosuppression they elicit in their mates. We also assayed for an interaction between male and female genotypes to test the specific hypothesis that the evolution of a trade-off between mating and immune defence in females might be being driven by sexual conflict. We found that females, but not males, harbour significant genetic variation for post-mating immunosuppression, and we did not detect an interaction between female and male genotypes. We thus conclude that post-mating immune depression is predominantly a ‘female’ trait, and find no evidence that it is evolving under sexual conflict.     

Fungi Associated with Females and Cysts of Heterodera glycines in a Florida Soybean Field

Fungal colonization was determined for females and cysts of Heterodera glycines on soybean roots or in rhizosphere soil from a Florida soybean field. A total of 1,620 females and cysts were examined in 1991, and 1,303 were examined in 1992. More than 35 species of fungi were isolated from females and cysts. The frequency of fungi colonizing white and yellow females was low, but a high frequency of fungi was encountered in brown cysts, which increased with time of exposure of the cysts to the soil. No single fungal species predominated in the nematode females or cysts in this field. Rarely was a female or cyst colonized by more than one fungus. The common fungi isolated from the females and cysts were Neocosmospora vasinfecta, Fusarium solani, Fusarium oxysporum, Dictyochaeta coffeae, Dictyochaeta heteroderae, Pyrenochaeta terrestris, Exophiala pisciphila, Gliocladium catenulatum, Stagonospora heteroderae, and a black yeast-like fungus. The communities of common fungal species isolated from cysts in several regions in the southeastern United States appear to be similar.     

Understanding context-dependency in plant-microbe symbiosis: The influence of abiotic and biotic contexts on host fitness and the rate of symbiont transmission

Understanding the dynamics of a hereditary symbiosis requires testing how ecological factors alter not only the fitness consequences of the symbiosis, but also the rate of symbiont transmission to the next generation. The relative importance of these two mechanisms remains unresolved because studies have not simultaneously examined how the ecological context of the symbiosis influences both costs/benefits and the rate of vertical transmission. Fungal endophytes in grasses have provided particularly tractable systems for investigating the ecological and evolutionary dynamics of hereditary symbiosis. Here we examine interactions between a fungal endophyte, Epichloë amarillans, and its grass host, Agrostis hyemalis, under altered abiotic and biotic contexts: a gradient of water availability and in the presence versus absence of soil microbes. We show that benefits of the symbiosis were strongest when water was limiting. Symbiotic plants at the lowest watering level produced ∼40% more inflorescences and greater seed mass than non-symbiotic plants, while at the highest watering level, symbiotic and non-symbiotic plants did not significantly differ in reproductive fitness. Benefits appear to accrue by allowing hosts to escape from drought, a response that has not been previously reported to be endophyte-mediated. Symbiotic plants at the lowest watering level flowered 9 days earlier than non-symbiotic plants. Interestingly, our results suggest the symbiosis may be costly in the presence of soil microbes, as on live soil, the biomass of symbiotic plants was lower than the biomass of symbiont-free plants. We detected no effect of either the biotic or abiotic context on the rate of symbiont vertical transmission, suggesting that the context-dependent benefits of the symbiosis are the more important driver of variation in symbiont frequency in this system.     

Rice BiP3 regulates immunity mediated by the PRRs XA3 and XA21 but not immunity mediated by the NB-LRR protein,Pi5

Plant innate immunity is mediated by pattern recognition receptors (PRRs) and intracellular NB-LRR (nucleotide-binding domain and leucine-rich repeat) proteins. Overexpression of the endoplasmic reticulum (ER) chaperone, luminal-binding protein 3 (BiP3) compromises resistance to Xanthomonas oryzae pv. oryzae (Xoo) mediated by the rice PRR XA21 [12]. Here we show that BiP3 overexpression also compromises resistance mediated by rice XA3, a PRR that provides broad-spectrum resistance to Xoo. In contrast, BiP3 overexpression has no effect on resistance mediated by rice Pi5, an NB-LRR protein that confers resistance to the fungal pathogen Magnaporthe oryzae (M. oryzae). Our results suggest that rice BiP3 regulates membrane-resident PRR-mediated immunity.     

Behavioural mimicry in flight path of Batesian intraspecific polymorphic butterfly Papilio polytes

Batesian mimics that show similar coloration to unpalatable models gain a fitness advantage of reduced predation. Beyond physical similarity, mimics often exhibit behaviour similar to their models, further enhancing their protection against predation by mimicking not only the model''s physical appearance but also activity. In butterflies, there is a strong correlation between palatability and flight velocity, but there is only weak correlation between palatability and flight path. Little is known about how Batesian mimics fly. Here, we explored the flight behaviour of four butterfly species/morphs: unpalatable model Pachliopta aristolochiae, mimetic and non-mimetic females of female-limited mimic Papilio polytes, and palatable control Papilio xuthus. We demonstrated that the directional change (DC) generated by wingbeats and the standard deviation of directional change (SDDC) of mimetic females and their models were smaller than those of non-mimetic females and palatable controls. Furthermore, we found no significant difference in flight velocity among all species/morphs. By showing that DC and SDDC of mimetic females resemble those of models, we provide the first evidence for the existence of behavioural mimicry in flight path by a Batesian mimic butterfly.     

Non-invasive Imaging of the Innate Immune Response in a Zebrafish Larval Model of Streptococcus iniae Infection

The aquatic pathogen, Streptococcus iniae, is responsible for over 100 million dollars in annual losses for the aquaculture industry and is capable of causing systemic disease in both fish and humans. A better understanding of S. iniae disease pathogenesis requires an appropriate model system. The genetic tractability and the optical transparency of the early developmental stages of zebrafish allow for the generation and non-invasive imaging of transgenic lines with fluorescently tagged immune cells. The adaptive immune system is not fully functional until several weeks post fertilization, but zebrafish larvae have a conserved vertebrate innate immune system with both neutrophils and macrophages. Thus, the generation of a larval infection model allows the study of the specific contribution of innate immunity in controlling S. iniae infection.The site of microinjection will determine whether an infection is systemic or initially localized. Here, we present our protocols for otic vesicle injection of zebrafish aged 2-3 days post fertilization as well as our techniques for fluorescent confocal imaging of infection. A localized infection site allows observation of initial microbe invasion, recruitment of host cells and dissemination of infection. Our findings using the zebrafish larval model of S. iniae infection indicate that zebrafish can be used to examine the differing contributions of host neutrophils and macrophages in localized bacterial infections. In addition, we describe how photolabeling of immune cells can be used to track individual host cell fate during the course of infection.     

Sex-linked transcriptional divergence in the hermaphrodite fungus Neurospora tetrasperma

In the filamentous ascomycete Neurospora tetrasperma, a large (approx. 7 Mbp) region of suppressed recombination surrounds the mating-type (mat) locus. While the remainder of the genome is largely homoallelic, this region of recombinational suppression, extending over 1500 genes, is associated with sequence divergence. Here, we used microarrays to examine how the molecular phenotype of gene expression level is linked to this divergent region, and thus to the mating type. Culturing N. tetrasperma on agar media that induce sexual/female or vegetative/male tissue, we found 196 genes significantly differentially expressed between mat A and mat a mating types. Our data show that the genes exhibiting mat-linked expression are enriched in the region genetically linked to mating type, and sequence and expression divergence are positively correlated. Our results indicate that the phenotype of mat A strains is optimized for traits promoting sexual/female development and the phenotype of mat a strains for vegetative/male development. This discovery of differentially expressed genes associated with mating type provides a link between genotypic and phenotypic divergence in this taxon and illustrates a fungal analogue to sexual dimorphism found among animals and plants.     

An Experimental Model to Study Tuberculosis-Malaria Coinfection upon Natural Transmission of Mycobacterium tuberculosis and Plasmodium berghei

Coinfections naturally occur due to the geographic overlap of distinct types of pathogenic organisms. Concurrent infections most likely modulate the respective immune response to each single pathogen and may thereby affect pathogenesis and disease outcome. Coinfected patients may also respond differentially to anti-infective interventions. Coinfection between tuberculosis as caused by mycobacteria and the malaria parasite Plasmodium, both of which are coendemic in many parts of sub-Saharan Africa, has not been studied in detail. In order to approach the challenging but scientifically and clinically highly relevant question how malaria-tuberculosis coinfection modulate host immunity and the course of each disease, we established an experimental mouse model that allows us to dissect the elicited immune responses to both pathogens in the coinfected host. Of note, in order to most precisely mimic naturally acquired human infections, we perform experimental infections of mice with both pathogens by their natural routes of infection, i.e. aerosol and mosquito bite, respectively.     

Transgenerational effects of sexual interactions and sexual conflict: non-sires boost the fecundity of females in the following generation

The consequences of sexual interactions extend beyond the simple production of offspring. These interactions typically entail direct effects on female fitness, but may also impact the life histories of later generations. Evaluating the cross-generational effects of sexual interactions provides insights into the dynamics of sexual selection and conflict. Such studies can elucidate whether offspring fitness optima diverge across sexes upon heightened levels of sexual interaction among parents. Here, we found that, in Drosophila melanogaster, components of reproductive success in females, but not males, were contingent on the nature of sexual interactions experienced by their mothers. In particular, maternal sexual interactions with non-sires enhanced female fecundity in the following generation. This highlights the importance of non-sire influences of sexual interactions on the expression of offspring life histories.     

Viability of Heterodera glycines Exposed to Fungal Filtrates

Filtrates from nematode-parasitic fungi have been reported to be toxic to plant-parasitic nematodes. Our objective was to determine the effects of fungal filtrates on second-stage juveniles and eggs of Heterodera glycines. Eleven fungal species that were isolated from cysts extracted from a soybean field in Florida were tested on J2, and five species were tested on eggs in vitro. Each fungal species was grown in Czapek-Dox broth and malt extract broth. No toxic activity was observed for fungi grown in Czapek-Dox broth. Filtrates from Paecilomyces lilacinus, Stagonospora heteroderae, Neocosmospora vasinfecta, and Fusarium solani grown in malt extract broth were toxic to J2, whereas filtrates from Exophiala pisciphila, Fusarium oxysporum, Gliocladium catenulatum, Pyrenochaeta terrestris, Verticillium chlamydosporium, and sterile fungi 1 and 2 were not toxic to J2. Filtrates of P. lilacinus, S. heteroderae, and N. vasinfecta grown in malt extract broth reduced egg viability, whereas F. oxysporum and P. terrestris filtrates had no effect on egg viability.