Maternal effects in disease resistance: poor maternal environment increases offspring resistance to an insect virus

The maternal energetic environment affects both egg and offspring phenotypes in green anole lizards (Anolis carolinensis)

Animals exist in dynamic environments that may affect both their own fitness and that of their offspring. Maternal effects might allow mothers to prepare their offspring for the environment in which they will be born via several mechanisms, not all of which are well understood. Resource scarcity and forced resource allocation are two scenarios that could affect maternal investment by altering the amount and type of resources available for investment in offspring, albeit in potentially different ways. We tested the hypothesis that maternal dietary restriction and sprint training have different consequences for the offspring phenotype in an oviparous lizard (Anolis carolinensis). To do this, we collected and reared eggs from adult diet-manipulated females (low-diet [LD] or high-diet [HD]) and sprint-trained females (sprint trained [ST] or untrained [UT]) and measured both egg characteristics and hatchling morphology. ST and LD mothers laid both the fewest and heaviest eggs, and ST, UT, and LD eggs also had significantly longer incubation periods than the HD group. Hatchlings from the diet experiment (LD and HD offspring) were the heaviest overall. Furthermore, both body mass of the mother at oviposition and change in maternal body mass over the course of the experiment had significant and sometimes different effects on egg and offspring phenotypes, highlighting the importance of maternal energetic state to the allocation of maternal resources.

Sugar-rich larval diet promotes lower adult pathogen load and higher survival after infection in a polyphagous fly

Nutrition is a central factor influencing immunity and resistance to infection, but the extent to which nutrition during development affects adult responses to infections is poorly understood. Our study investigated how the nutritional composition of the larval diet affects the survival, pathogen load, and food intake of adult fruit flies, Bactrocera tryoni, after septic bacterial infection. We found a sex-specific effect of larval diet composition on survival post-infection: survival rate was higher and bacterial load was lower for infected females fed sugar-rich larval diet compared with females fed protein-rich larval diet, an effect that was absent in males. Both males and females were heavier when fed a balanced larval diet compared to protein- or sugar-rich diet, while body lipid reserves were higher in the sugar-rich larval diet compared with other diets. Body protein reserve was lower for sugar-rich larval diets compared to other diets in males, but not females. Both females and males shifted their nutrient intake to ingest a sugar-rich diet when infected compared with sham-infected flies without any effect of the larval diet, suggesting that sugar-rich diets can be beneficial to fight off bacterial infection as shown in previous literature. Overall, our findings show that nutrition during early life can shape individual fitness in adulthood.

No evidence for increased fitness of offspring from multigenerational effects of parental size or natal carcass size in the burying beetle Nicrophorus marginatus

Multigenerational effects (often called maternal effects) are components of the offspring phenotype that result from the parental phenotype and the parental environment as opposed to heritable genetic effects. Multigenerational effects are widespread in nature and are often studied because of their potentially important effects on offspring traits. Although multigenerational effects are commonly observed, few studies have addressed whether they affect offspring fitness. In this study we assess the effect of potential multigenerational effects of parental body size and natal carcass size on lifetime fitness in the burying beetle, Nicrophorus marginatus (Coleoptera; Silphidae). Lifespan, total number of offspring, and number of offspring in the first reproductive bout were not significantly related to parental body size or natal carcass size. However, current carcass size used for reproduction was a significant predictor for lifetime number of offspring and number of offspring in the first brood. We find no evidence that multigenerational effects from larger parents or larger natal carcasses contribute to increased fitness of offspring.

Transgenerational Effects of Parental Diet on Offspring Development and Disease Resistance in Flies

The environmental conditions experienced by parents influence next generations, with the parental nutritional status playing an important role in shaping offspring phenotypes. Our understanding of transgenerational effects of parental diet on offspring pathogen resistance is, however, poorly documented. We manipulated the quality of parental diet (i.e., mother, father, or both) and measured effects on offspring development and survival after an immune challenge by septic infection. We used Bactrocera tryoni as host model infected with the pathogenic bacterium, Serratia marcescens. Our results showed no significant effect of maternal, or paternal, diet on offspring resistance. Interestingly, when the diet of both parents was manipulated, sons from parents fed either carbohydrate- or protein-biased diets had higher survival upon pathogen infection than sons from parents fed balanced diets. The quality of the parental diet had no effect on offspring developmental traits with the exception of egg hatching percentage which decreased when mothers were fed a protein-biased diet. Our results emphasised the complexity of nutritional transgenerational effects on offspring pathogen resistance and development.

Paternal and maternal effects in a mosquito: A bridge for life history transition

Parental (transgenerational) effects occur when the conditions experienced by a mother or father contribute to offspring phenotype. Here we show that parental larval diet in mosquitoes, Aedes aegypti, results in differential allocation of resources in offspring of parents depending on the nutritional condition (quality) of their mate. Maternal effects influenced the number of eggs produced by females as well as their lipid investment. Low nutrient females mated with high nutrient males laid eggs with significantly higher lipid content than those laid by high nutrient females. Paternal effects showed that when high nutrient males mated with low nutrient females, resulting eggs had higher lipid content than when low nutrient males mated with low nutrient females. Overall, our results are consistent with a pattern predicted by the differential allocation of resources hypothesis, when females experience nutritional deprivation, which asserts that mate quality directly influences reproductive allocation.

Trans-generational viral transmission and immune priming are dose-dependent

It is becoming increasingly apparent that trans-generational immune priming (i.e. the transfer of the parental immunological experience to its progeny resulting in offspring protection from pathogens that persist across generations) is a common phenomenon not only in vertebrates, but also invertebrates. Likewise, it is known that covert pathogenic infections may become 'triggered' into an overt infection by various stimuli, including exposure to heterologous infections. Yet, rarely have both phenomena been explored in parallel. Using as a model system the African armyworm Spodoptera exempta, an eruptive agricultural pest and its endemic dsDNA virus (Spodoptera exempta nucleopolyhedrovirus, SpexNPV), the aim of this study was to explore the impact of parental inoculating-dose on trans-generational pathogen transmission and immune priming (in its broadest sense). Larvae were orally challenged with one of five doses of SpexNPV and survivors from these treatments were mated and their offspring monitored for viral mortality. Offspring from parents challenged with low viral doses showed evidence of 'immune priming' (i.e. enhanced survival following SpexNPV challenge); in contrast, offspring from parents challenged with higher viral doses exhibited greater susceptibility to viral challenge. Most offspring larvae died of the virus they were orally challenged with; in contrast, most offspring from parents that had been challenged with the highest doses were killed by the vertically transmitted virus (90%) and not the challenge virus. These results demonstrate that the outcome of a potentially lethal virus challenge is critically dependent on the level of exposure to virus in the parental generation-either increasing resistance at very low parental viral doses (consistent with trans-generational immune priming) or increasing susceptibility at higher parental doses (consistent with virus triggering). We discuss the implications of these findings for understanding both natural epizootics of baculoviruses and for using them as biological control agents.

Experimental evidence that local interactions select against selfish behaviour

How social behaviours evolve remains one of the most debated questions in evolutionary biology. An important theoretical prediction is that when organisms interact locally due to limited dispersal or strong social ties, the population structure that emerges may favour cooperation over antagonism. We carry out an experimental test of this theory by directly manipulating population spatial structure in an insect laboratory model system and measuring the impact on the evolution of the extreme selfish behaviour of cannibalism. We show that, as predicted by the theory, Indian meal moth larvae that evolved in environments with more limited dispersal are selected for lower rates of cannibalism. This is important because it demonstrates that local interactions select against selfish behaviour. Therefore, the ubiquitous variation in population structure that we see in nature is a simple mechanism that can help to explain the variation in selfish and cooperative behaviours that we see in nature.

Pathogen Dynamics across the Diversity of Aging

AbstractReproduction, mortality, and immune function often change with age but do not invariably deteriorate. Across the tree of life, there is extensive variation in age-specific performance and changes to key life-history traits. These changes occur on a spectrum from classic senescence, where performance declines with age, to juvenescence, where performance improves with age. Reproduction, mortality, and immune function are also important factors influencing the spread of infectious disease, yet there exists no comprehensive investigation into how the aging spectrum of these traits impacts epidemics. We used a model laboratory infection system to compile an aging profile of a single organism, including traits directly linked to pathogen susceptibility and those that should indirectly alter pathogen transmission by influencing demography. We then developed generalizable epidemiological models demonstrating that different patterns of aging produce dramatically different transmission landscapes: in many cases, aging can reduce the probability of epidemics, but it can also promote severity. This work provides context and tools for use across taxa by empiricists, demographers, and epidemiologists, advancing our ability to accurately predict factors contributing to epidemics or the potential repercussions of senescence manipulation.

Resource quality determines the evolution of resistance and its genetic basis

Parasites impose strong selection on their hosts, but the level of any evolved resistance may be constrained by the availability of resources. However, studies identifying the genomic basis of such resource-mediated selection are rare, particularly in nonmodel organisms. Here, we investigated the role of nutrition in the evolution of resistance to a DNA virus (PiGV), and any associated trade-offs in a lepidopteran pest species (Plodia interpunctella). Through selection experiments and whole-genome resequencing, we identify genetic markers of resistance that vary between the nutritional environments during selection. We do not find consistent evolution of resistance in the presence of virus but rather see substantial variation among replicate populations. Resistance in a low-nutrition environment is negatively correlated with growth rate, consistent with an established trade-off between immunity and development, but this relationship is highly context dependent. Whole-genome resequencing of the host shows that resistance mechanisms are likely to be highly polygenic and although the underlying genetic architecture may differ between high and low-nutrition environments, similar mechanisms are commonly used. As a whole, our results emphasize the importance of the resource environment on influencing the evolution of resistance.

Disentangling non-specific and specific transgenerational immune priming components in host-parasite interactions

Exposure to a pathogen primes many organisms to respond faster or more efficiently to subsequent exposures. Such priming can be non-specific or specific, and has been found to extend across generations. Disentangling and quantifying specific and non-specific effects is essential for understanding the genetic epidemiology of a system. By combining a large infection experiment and mathematical modelling, we disentangle different transgenerational effects in the crustacean model Daphnia magna exposed to different strains of the bacterial parasite Pasteuria ramosa. In the experiment, we exposed hosts to a high dose of one of three parasite strains, and subsequently challenged their offspring with multiple doses of the same (homologous) or a different (heterologous) strain. We find that exposure of Daphnia to Pasteuria decreases the susceptibility of their offspring by approximately 50%. This transgenerational protection is not larger for homologous than for heterologous parasite challenges. Methodologically, our work represents an important contribution not only to the analysis of immune priming in ecological systems but also to the experimental assessment of vaccines. We present, for the first time, an inference framework to investigate specific and non-specific effects of immune priming on the susceptibility distribution of hosts—effects that are central to understanding immunity and the effect of vaccines.

Understanding the Evolutionary Ecology of host--pathogen Interactions Provides Insights into the Outcomes of Insect Pest Biocontrol

The use of viral pathogens to control thepopulation size of pest insects has produced both successful and unsuccessful outcomes. Here, we investigate whether those biocontrol successes and failures can be explained by key ecological and evolutionary processes between hosts and pathogens. Specifically, we examine how heterogeneity inpathogen transmission, ecological and evolutionary tradeoffs, andpathogen diversity affect insect population density and thus successful control. Wefirst review theexisting literature and then use numerical simulations of mathematical models to further explore these processes. Our results show that thecontrol of insect densities using viruses depends strongly on theheterogeneity of virus transmission among insects. Overall, increased heterogeneity of transmission reduces theeffect of viruses on insect densities and increases thelong-term stability of insect populations. Lower equilibrium insect densities occur when transmission is heritable and when there is atradeoff between mean transmission and insect fecundity compared to when theheterogeneity of transmission arises from non-genetic sources. Thus, theheterogeneity of transmission is akey parameter that regulates thelong-term population dynamics of insects and their pathogens. Wealso show that both heterogeneity of transmission and life-history tradeoffs modulate characteristics of population dynamics such as thefrequency and intensity of ``boom--bust" population cycles. Furthermore, we show that because of life-history tradeoffs affecting thetransmission rate, theuse of multiple pathogen strains is more effective than theuse of asingle strain to control insect densities only when thepathogen strains differ considerably intheir transmission characteristics. By quantifying theeffects of ecology and evolution on population densities, we are able to offer recommendations to assess thelong-term effects of classical biocontrol.

Trans-generational Immune Priming in Invertebrates: Current Knowledge and Future Prospects

Trans-generational immune priming (TGIP) refers to the transfer of the parental immunological experience to its progeny. This may result in offspring protection from repeated encounters with pathogens that persist across generations. Although extensively studied in vertebrates for over a century, this phenomenon has only been identified 20 years ago in invertebrates. Since then, invertebrate TGIP has been the focus of an increasing interest, with half of studies published during the last few years. TGIP has now been tested in several invertebrate systems using various experimental approaches and measures to study it at both functional and evolutionary levels. However, drawing an overall picture of TGIP from available studies still appears to be a difficult task. Here, we provide a comprehensive review of TGIP in invertebrates with the objective of confronting all the data generated to date to highlight the main features and mechanisms identified in the context of its ecology and evolution. To this purpose, we describe all the articles reporting experimental investigation of TGIP in invertebrates and propose a critical analysis of the experimental procedures performed to study this phenomenon. We then investigate the outcome of TGIP in the offspring and its ecological and evolutionary relevance before reviewing the potential molecular mechanisms identified to date. In the light of this review, we build hypothetical scenarios of the mechanisms through which TGIP might be achieved and propose guidelines for future investigations.

Maternal Stress Reduces the Susceptibility of Root-Knot Nematodes to Pasteuria Penetrans

Pasteuria penetrans is an obligate parasite of root-knot nematodes (Meloidogyne spp.). Endospores of P. penetrans attach to the cuticle of second-stage juveniles (J2) and complete their life cycle within the nematode female body. Infected females will be filled with spores and will be sterilized. Studies with Daphnia magna and its parasite Pasteuria ramosa showed that a poor maternal environment can lead to offspring resistant to P. ramosa. Therefore, we hypothesized that Meloidogyne arenaria females raised under a stressed environment would produce offspring that were more resistant to P. penetrans. Females were exposed to a stressed environment created by crowding and low-food supply, or a non-stressed environment and their offspring evaluated for endospore attachment and infection by P. penetrans. No difference in spore attachment was observed between the two treatments. However, infection rate of P. penetrans in the stressed treatment was significantly lower than that in the non-stressed treatment (8 vs 18%). Mothers raised under stressed conditions appeared to produce more resistant offspring than did mothers raised under favorable conditions. Under stressful conditions, M. arenaria mothers may provide their progeny with enhanced survival traits. In the field, when nematode populations are not managed, they often reach the carrying capacity of their host plant by the end of the season. This study suggests that the next generation of inoculum may be more resistant to infection by P. penetrans.

Parasite rearing and infection temperatures jointly influence disease transmission and shape seasonality of epidemics

Seasonal epidemics erupt commonly in nature and are driven by numerous mechanisms. Here, we suggest a new mechanism that could determine the size and timing of seasonal epidemics: rearing environment changes the performance of parasites. This mechanism arises when the environmental conditions in which a parasite is produced impact its performance-independently from the current environment. To illustrate the potential for "rearing effects", we show how temperature influences infection risk (transmission rate) in a Daphnia-fungus disease system through both parasite rearing temperature and infection temperature. During autumnal epidemics, zooplankton hosts contact (eat) fungal parasites (spores) reared in a gradually cooling environment. To delineate the effect of rearing temperature from temperature at exposure and infection, we used lab experiments to parameterize a mechanistic model of transmission rate. We also evaluated the rearing effect using spores collected from epidemics in cooling lakes. We found that fungal spores were more infectious when reared at warmer temperatures (in the lab and in two of three lakes). Additionally, the exposure (foraging) rate of hosts increased with warmer infection temperatures. Thus, both mechanisms cause transmission rate to drop as temperature decreases over the autumnal epidemic season (from summer to winter). Simulations show how these temperature-driven changes in transmission rate can induce waning of epidemics as lakes cool. Furthermore, via thermally dependent transmission, variation in environmental cooling patterns can alter the size and shape of epidemics. Thus, the thermal environment drives seasonal epidemics through effects on hosts (exposure rate) and the infectivity of parasites (a rearing effect). Presently, the generality of parasite rearing effects remains unknown. Our results suggest that they may provide an important but underappreciated mechanism linking temperature to the seasonality of epidemics.

Trans-generational immune priming in the mealworm beetle protects eggs through pathogen-dependent mechanisms imposing no immediate fitness cost for the offspring

Immune-challenged mothers can improve their offspring immunity through trans-generational immune priming (TGIP). In insects, TGIP endows the offspring with lifetime immunity, including the eggs, which are likely exposed soon after maternal infection. Egg protection may rely on the transfer of maternal immune effectors to the egg or/and the induction of egg immune genes. These respective mechanisms are assumed to have early-life fitness costs of different magnitude for the offspring. We provide evidence in the mealworm beetle Tenebrio molitor that enhanced egg immunity following a maternal immune challenge is achieved by both of these mechanisms but in a pathogen-dependent manner. While previously found having late-life fitness costs for the offspring, TGIP here improved egg hatching success and early larval survival, in addition of improving offspring immunity. These results suggest that early-life of primed offspring is critical in the optimization of life history trajectory of this insect under trans-generational pathogenic threats.

Responses to a warming world: Integrating life history, immune investment, and pathogen resistance in a model insect species

Environmental temperature has important effects on the physiology and life history of ectothermic animals, including investment in the immune system and the infectious capacity of pathogens. Numerous studies have examined individual components of these complex systems, but little is known about how they integrate when animals are exposed to different temperatures. Here, we use the Indian meal moth (Plodia interpunctella) to understand how immune investment and disease resistance react and potentially trade‐off with other life‐history traits. We recorded life‐history (development time, survival, fecundity, and body size) and immunity (hemocyte counts, phenoloxidase activity) measures and tested resistance to bacterial (E. coli) and viral (Plodia interpunctella granulosis virus) infection at five temperatures (20–30°C). While development time, lifespan, and size decreased with temperature as expected, moths exhibited different reproductive strategies in response to small changes in temperature. At cooler temperatures, oviposition rates were low but tended to increase toward the end of life, whereas warmer temperatures promoted initially high oviposition rates that rapidly declined after the first few days of adult life. Although warmer temperatures were associated with strong investment in early reproduction, there was no evidence of an associated trade‐off with immune investment. Phenoloxidase activity increased most at cooler temperatures before plateauing, while hemocyte counts increased linearly with temperature. Resistance to bacterial challenge displayed a complex pattern, whereas survival after a viral challenge increased with rearing temperature. These results demonstrate that different immune system components and different pathogens can respond in distinct ways to changes in temperature. Overall, these data highlight the scope for significant changes in immunity, disease resistance, and host–parasite population dynamics to arise from small, biologically relevant changes to environmental temperature. In light of global warming, understanding these complex interactions is vital for predicting the potential impact of insect disease vectors and crop pests on public health and food security.

The activity of phenoloxidase in haemolymph plasma is not a predictor of Lymantria dispar resistance to its baculovirus

Host innate immunity is one of the factors that determines the resistance of insects to their entomopathogens. In the research reported here we studied whether or not phenoloxidase (PO), a key enzyme in the melanogenesis component of humoral immunity of insects, plays a role in the protection of Lymantria dispar larvae from infection by L. dispar multiple nucleopolyhedrovirus. We studied two types of viral infection: overt and covert. The following lines of investigation were tested: i) the intravital individual estimation of baseline PO activity in haemolymph plasma followed by virus challenging; ii) the specific inhibition of PO activity in vivo by peroral treatment of infected larvae with phenylthiourea (PTU), a competitive inhibitor of PO; iii) the evaluation of PO activity in the haemolymph plasma after larval starvation. Starvation is a stress that activates the covert infection to an overt form. All of these experiments did not show a relationship between PO activity in haemolymph plasma of L. dispar larvae and larval susceptibility to baculovirus. Moreover, starvation-induced activation of covert viral infection to an overt form occurred in 70 percent of virus-carrying larvae against the background of a dramatic increase of PO activity in haemolymph plasma in the insects studied. Our conclusion is that in L. dispar larvae PO activity is not a predictor of host resistance to baculovirus.

Disease spread in age structured populations with maternal age effects

Fundamental ecological processes, such as extrinsic mortality, determine population age structure. This influences disease spread when individuals of different ages differ in susceptibility or when maternal age determines offspring susceptibility. We show that Daphnia magna offspring born to young mothers are more susceptible than those born to older mothers, and consider this alongside previous observations that susceptibility declines with age in this system. We used a susceptible‐infected compartmental model to investigate how age‐specific susceptibility and maternal age effects on offspring susceptibility interact with demographic factors affecting disease spread. Our results show a scenario where an increase in extrinsic mortality drives an increase in transmission potential. Thus, we identify a realistic context in which age effects and maternal effects produce conditions favouring disease transmission.

Bigger is better: changes in body size explain a maternal effect of food on offspring disease resistance

Maternal effects triggered by changes in the environment (e.g., nutrition or crowding) can influence the outcome of offspring–parasite interactions, with fitness consequences for the host and parasite. Outside of the classic example of antibody transfer in vertebrates, proximate mechanisms have been little studied, and thus, the adaptive significance of maternal effects on infection is not well resolved. We sought to determine why food‐stressed mothers give birth to offspring that show a low rate of infection when the crustacean Daphnia magna is exposed to an orally infective bacterial pathogen. These more‐resistant offspring are also larger at birth and feed at a lower rate. Thus, reduced disease resistance could result from slow‐feeding offspring ingesting fewer bacterial spores or because their larger size allows for greater immune investment. To distinguish between these theories, we performed an experiment in which we measured body size, feeding rate, and susceptibility, and were able to show that body size is the primary mechanism causing altered susceptibility: Larger Daphnia were less likely to become infected. Contrary to our predictions, there was also a trend that fast‐feeding Daphnia were less likely to become infected. Thus, our results explain how a maternal environmental effect can alter offspring disease resistance (though body size), and highlight the potential complexity of relationship between feeding rate and susceptibility in a host that encounters a parasite whilst feeding.

The trans-generational impact of population density signals on host-parasite interactions

Background

The density of a host population is a key parameter underlying disease transmission, but it also has implications for the expression of disease through its effect on host physiology. In response to higher densities, individuals are predicted to either increase their immune investment in response to the elevated risk of parasitism, or conversely to decrease their immune capacity as a consequence of the stress of a crowded environment. However, an individual’s health is shaped by many different factors, including their genetic background, current environmental conditions, and maternal effects. Indeed, population density is often sensed through the presence of info-chemicals in the environment, which may influence a host’s interaction with parasites, and also those of its offspring. All of which may alter the expression of disease, and potentially uncouple the presumed link between changes in host density and disease outcomes.

Results

In this study, we used the water flea Daphnia magna and its obligate bacterial parasite Pasteuria ramosa, to investigate how signals of high host density impact on host-parasite interactions over two consecutive generations. We found that the chemical signals from crowded treatments induced phenotypic changes in both the parental and offspring generations. In the absence of a pathogen, life-history changes were genotype-specific, but consistent across generations, even when the signal of density was removed. In contrast, the influence of density on infected animals depended on the trait and generation of exposure. When directly exposed to signals of high-density, host genotypes responded differently in how they minimised the severity of disease. Yet, in the subsequent generation, the influence of density was rarely genotype-specific and instead related to ability of the host to minimise the onset of infection.

Conclusion

Our findings reveal that population level correlations between host density and infection capture only part of the complex relationship between crowding and the severity of disease. We suggest that besides its role in horizontal transmission, signals of density can influence parasite epidemiology by modifying mechanisms of resistance across multiple generations, and elevating variability via genotype-by-environment interactions. Our results help resolve why some studies are able to find a positive correlation between high density and resistance, while others uncover a negative correlation, or even no direct relationship at all.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0828-4) contains supplementary material, which is available to authorized users.

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

Background

Recently, 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.

Methods

Metazoan 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.

Results

Metazoan 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.

Conclusions

Scientific 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 material

The online version of this article (doi:10.1186/s13071-016-1867-9) contains supplementary material, which is available to authorized users.

The Complete Genome Sequence of Plodia Interpunctella Granulovirus: Evidence for Horizontal Gene Transfer and Discovery of an Unusual Inhibitor-of-Apoptosis Gene

The Indianmeal moth, Plodia interpunctella (Lepidoptera: Pyralidae), is a common pest of stored goods with a worldwide distribution. The complete genome sequence for a larval pathogen of this moth, the baculovirus Plodia interpunctella granulovirus (PiGV), was determined by next-generation sequencing. The PiGV genome was found to be 112, 536 bp in length with a 44.2% G+C nucleotide distribution. A total of 123 open reading frames (ORFs) and seven homologous regions (hrs) were identified and annotated. Phylogenetic inference using concatenated alignments of 36 baculovirus core genes placed PiGV in the “b” clade of viruses from genus Betabaculovirus with a branch length suggesting that PiGV represents a distinct betabaculovirus species. In addition to the baculovirus core genes and orthologues of other genes found in other betabaculovirus genomes, the PiGV genome sequence contained orthologues of the bidensovirus NS3 gene, as well as ORFs that occur in alphabaculoviruses but not betabaculoviruses. While PiGV contained an orthologue of inhibitor of apoptosis-5 (iap-5), an orthologue of inhibitor of apoptosis-3 (iap-3) was not present. Instead, the PiGV sequence contained an ORF (PiGV ORF81) encoding an IAP homologue with sequence similarity to insect cellular IAPs, but not to viral IAPs. Phylogenetic analysis of baculovirus and insect IAP amino acid sequences suggested that the baculovirus IAP-3 genes and the PiGV ORF81 IAP homologue represent different lineages arising from more than one acquisition event. The presence of genes from other sources in the PiGV genome highlights the extent to which baculovirus gene content is shaped by horizontal gene transfer.

Transgenerational effect of infection in Plasmodium-infected mosquitoes

Transgenerational effects of infection have a huge potential to influence the prevalence and intensity of infections in vectors and, by extension, disease epidemiology. These transgenerational effects may increase the fitness of offspring through the transfer of protective immune factors. Alternatively, however, infected mothers may transfer the costs of infection to their offspring. Although transgenerational immune protection has been described in a dozen invertebrate species, we still lack a complete picture of the incidence and importance of transgenerational effects of infection in most invertebrate groups. The existence of transgenerational infection effects in mosquito vectors is of particular interest because of their potential for influencing parasite prevalence and intensity and, by extension, disease transmission. Here we present what we believe to be the first study on transgenerational infection effects in a mosquito vector infected with malaria parasites. The aim of this experiment was to quantify both the benefits and the costs of having an infected mother. We find no evidence of transgenerational protection in response to a Plasmodium infection. Having an infected mother does, however, entail considerable fecundity costs for the offspring: fecundity loss is three times higher in infected offspring issued from infected mothers than in infected offspring issued from uninfected mothers. We discuss the implications of our results and we call for more studies looking at transgenerational effects of infection in disease vectors.

Transgenerational effects modulate density-dependent prophylactic resistance to viral infection in a lepidopteran pest

There is an increasing appreciation of the importance of transgenerational effects on offspring fitness, including in relation to immune function and disease resistance. Here, we assess the impact of parental rearing density on offspring resistance to viral challenge in an insect species expressing density-dependent prophylaxis (DDP); i.e. the adaptive increase in resistance or tolerance to pathogen infection in response to crowding. We quantified survival rates in larvae of the cotton leafworm (Spodoptera littoralis) from either gregarious- or solitary-reared parents following challenge with the baculovirus S. littoralis nucleopolyhedrovirus. Larvae from both the parental and offspring generations exhibited DDP, with gregarious-reared larvae having higher survival rates post-challenge than solitary-reared larvae. Within each of these categories, however, survival following infection was lower in those larvae from gregarious-reared parents than those from solitary-reared, consistent with a transgenerational cost of DDP immune upregulation. This observation demonstrates that crowding influences lepidopteran disease resistance over multiple generations, with potential implications for the dynamics of host-pathogen interactions.

Genetic variation of transgenerational plasticity of offspring germination in response to salinity stress and the seed transcriptome of Medicago truncatula

BACKGROUND

Transgenerational plasticity provides phenotypic variation that contributes to adaptation. For plants, the timing of seed germination is critical for offspring survival in stressful environments, as germination timing can alter the environmental conditions a seedling experiences. Stored seed transcripts are important determinants of seed germination, but have not previously been linked with transgenerational plasticity of germination behavior. In this study we used RNAseq and growth chamber experiments of the model legume M. trucantula to test whether parental exposure to salinity stress influences the expression of stored seed transcripts and early offspring traits and test for genetic variation.

RESULTS

We detected genotype-dependent parental environmental effects (transgenerational plasticity) on the expression levels of stored seed transcripts, seed size, and germination behavior of four M. truncatula genotypes. More than 50% of the transcripts detected in the mature, ungerminated seed transcriptome were annotated as regulating seed germination, some of which are involved in abiotic stress response and post-embryonic development. Some genotypes showed increased seed size in response to parental exposure to salinity stress, but no parental environmental influence on germination timing. In contrast, other genotypes showed no seed size differences across contrasting parental conditions but displayed transgenerational plasticity for germimation timing, with significantly delayed germination in saline conditions when parental plants were exposed to salinity. In genotypes that show significant transgenerational plastic germination response, we found significant coexpression networks derived from salt responsive transcripts involved in post-transcriptional regulation of the germination pathway. Consistent with the delayed germination response to saline conditions in these genotypes, we found genes associated with dormancy and up-regulation of abscisic acid (ABA).

CONCLUSIONS

Our results demonstrate genetic variation in transgenerational plasticity within M. truncatula and show that parental exposure to salinity stress influences the expression of stored seed transcripts, seed weight, and germination behavior. Furthermore, we show that the parental environment influences gene expression to modulate biological pathways that are likely responsible for offspring germination responses to salinity stress.

A heavy legacy: offspring of malaria-infected mosquitoes show reduced disease resistance

Background

Trans-generational effects of immune stimulation may have either adaptive (trans-generational immune priming) or non-adaptive (fitness costs) effects on offspring ability to fight pathogens.

Methods

Anopheles coluzzii and its natural malaria parasite Plasmodium falciparum were used to test how maternal parasite infection affected offspring resistance to the same parasite species.

Results

Daughters of exposed mothers had similar qualitative resistance, as measured by their ability to prevent infection, relative to those of control mothers. However, maternal disease exposure altered offspring quantitative resistance, measured as the ability to limit parasite development, with mosquitoes of infected mothers suffering slightly increased parasite intensity compared to controls. In addition, quantitative resistance was minimal in offspring of highly infected mothers, and in offspring issued from eggs produced during the early infection phase.

Conclusions

Plasmodium falciparum infection in An. coluzzii can have trans-generational costs, lowering quantitative resistance in offspring of infected mothers. Malaria-exposed mosquitoes might heavily invest in immune defences and thereby produce lower quality offspring that are poorly resistant.

Electronic supplementary material

The online version of this article (doi:10.1186/1475-2875-13-442) contains supplementary material, which is available to authorized users.

Maternal transfer of immunity in scallop Chlamys farreri and its trans-generational immune protection to offspring against bacterial challenge

Maternal immunity plays a crucial role in protecting the offspring at early stages of life and contributes a trans-generational effect on the offspring's phenotype. In the present study, maternal transfer of immunity and its trans-generational effect on offspring in scallop Chlamys farreri were investigated. The proteins including CfLGBP, CfLBP/BPI, CfLYZ and CfCu/Zn-SOD existed in the scallop eggs with high level while CfLec-3 was not detected. In contrast, the mRNA levels of these proteins were extremely low except that of CfCu/Zn-SOD. The protein extracts of scallop eggs exhibited remarkable agglutination activity and bactericidal effect against gram-negative bacteria Escherichia coli and Vibro anguillarum, and fungi Pichia pastoris. When the maternal scallops were stimulated with heat-killed V. anguillarum, the mRNA levels of CfLBP/BPI and CfLYZ in their offspring were expressed significant higher in D-shaped larvae. Furthermore, the protein levels of CfLBP/BPI and CfCu/Zn-SOD in the offspring of maternal immune stimulation group were higher than that of control at almost all the developmental stages, while the level of CfLec-3 and CfLYZ was higher than that of control just in eggs or trochophore, respectively. A significant enhancement of Cu/Zn-SOD and antibacterial activities was also observed in eggs, 4-cell embryos and trochophore of offspring from immune stimulated mother scallops. Moreover, the mortality of offspring from the immune stimulated mother scallops was significantly lower than that of control after bacterial challenge, especially in trochophore. The results indicated that scallop eggs or embryos received maternal derived immune competence to defense against the invading pathogens, and the maternal scallops received an immune stimulation endowed their offspring with a trans-generational immune capability to protect them against infections effectively.

Food availability and maternal immunization affect transfer and persistence of maternal antibodies in nestling pigeons

The ability of mothers to transfer antibodies (Abs) to their young and the temporal persistence of maternal Abs in offspring constitute important life-history traits that can impact the evolution of host-parasite interactions. Here, we examined the effects of food availability and parental immunization on the transfer and persistence of maternal antibodies in nestling pigeons (Columba livia). This species can transmit maternal Abs to offspring before hatching through the egg yolk and potentially after hatching through crop milk. However, the role of this postnatal substance in immunity remains elusive. We used a full cross-fostering design to disentangle the effects of food limitation and parental immunization both before and after hatching on the levels and persistence of maternal Abs in chicks. Parents were immunized via injection with keyhole limpet hemocyanin antigens. Using an immunoassay that specifically detected the IgY antibodies that are known to be transmitted via the yolk, we found that the levels of anti-KLH Abs in newly hatched chicks were positively correlated with the levels of anti-KLH Abs in the blood of their biological mothers. However, this correlation was not present between chicks and their foster parents, suggesting limited IgY transfer via crop milk to the chick's bloodstream. Interestingly, biological mothers subjected to food limitation during egg laying transferred significantly fewer specific maternal Abs, which suggests that the transfer of antibodies might be costly for them. In addition, the persistence of maternal Abs in a chick's bloodstream was not affected by food limitation or the foster parents' anti-KLH Ab levels; it was only affected by the initial level of maternal anti-KLH Abs that were present in newly hatched chicks. These results suggest that the maternal transfer of Abs could be costly but that their persistence in an offspring's bloodstream may not necessarily be affected by environmental conditions.

Dietary supply with polyunsaturated fatty acids and resulting maternal effects influence host--parasite interactions

Background

Interactions between hosts and parasites can be substantially modulated by host nutrition. Polyunsaturated fatty acids (PUFAs) are essential dietary nutrients; they are indispensable as structural components of cell membranes and as precursors for eicosanoids, signalling molecules which act on reproduction and immunity. Here, we explored the potential of dietary PUFAs to affect the course of parasitic infections using a well-established invertebrate host – parasite system, the freshwater herbivore Daphnia magna and its bacterial parasite Pasteuria ramosa.

Results

Using natural food sources differing in their PUFA composition and by experimentally modifying the availability of dietary arachidonic acid (ARA) and eicosapentaenoic acid (EPA) we examined PUFA-mediated effects resulting from direct consumption as well as maternal effects on offspring of treated mothers. We found that both host and parasite were affected by food quality. Feeding on C20 PUFA-containing food sources resulted in higher offspring production of hosts and these effects were conveyed to a great extent to the next generation. While feeding on a diet containing high PUFA concentrations significantly reduced the likelihood of becoming infected, the infection success in the next generation increased whenever the maternal diet contained PUFAs. We suggest that this opposing effect was caused by a trade-off between reproduction and immunity in the second generation.

Conclusions

Considering the direct and maternal effects of dietary PUFAs on host and parasite we propose that host – parasite interactions and thus disease dynamics under natural conditions are subject to the availability of dietary PUFAs.

Juvenile nutritional stress affects growth rate, adult organ mass, and innate immune function in zebra finches (Taeniopygia guttata)

Developmental conditions may influence many aspects of adult phenotype, including growth and immune function. Whether poor developmental environments impair both growth and immune function or induce a trade-off between the two processes is inconclusive, and the impact of the timing of stress in determining this relationship has so far been overlooked. We tested the hypothesis that the long-term effects of nutritional stress on growth, body composition, and immune function in zebra finches (Taeniopygia guttata) are different depending on whether stress is experienced during an early or a juvenile phase (i.e., before or after nutritional independence, respectively). We raised birds on high (H) or low (L) food conditions until posthatch day (PHD) 35 and switched treatments for half of the birds in each of the H and L groups from PHD 36 to 61. We found that unfavorable juvenile conditions (PHD 36-61) increased somatic growth rates and liver mass, body fat, and some aspects of immune function. We also observed a positive relationship between growth and immune function, as individuals that grew faster as juveniles also had better innate immune responses as adults. There was no effect of treatment on basal metabolic rate. These findings demonstrate the importance of juvenile developmental conditions in shaping multiple aspects of the adult phenotype.