Maternal transmission of immunity to white spot syndrome associated virus (WSSV) in shrimp (Penaeus monodon)

Experimental Infection Models and Their Usefulness for White Spot Syndrome Virus (WSSV) Research in Shrimp

White spot syndrome virus (WSSV) is marked as one of the most economically devastating pathogens in shrimp aquaculture worldwide. Infection of cultured shrimp can lead to mass mortality (up to 100%). Although progress has been made, our understanding of WSSV's infection process and the virus-host-environment interaction is far from complete. This in turn hinders the development of effective mitigation strategies against WSSV. Infection models occupy a crucial first step in the research flow that tries to elucidate the infectious disease process to develop new antiviral treatments. Moreover, since the establishment of continuous shrimp cell lines is a work in progress, the development and use of standardized in vivo infection models that reflect the host-pathogen interaction in shrimp is a necessity. This review critically examines key aspects of in vivo WSSV infection model development that are often overlooked, such as standardization, (post)larval quality, inoculum type and choice of inoculation procedure, housing conditions, and shrimp welfare considerations. Furthermore, the usefulness of experimental infection models for different lines of WSSV research will be discussed with the aim to aid researchers when choosing a suitable model for their research needs.

Infection risk by oral contamination does not induce immune priming in the mealworm beetle (Tenebrio molitor) but triggers behavioral and physiological responses

In invertebrates, immune priming is the ability of individuals to enhance their immune response based on prior immunological experiences. This adaptive-like immunity likely evolved due to the risk of repeated infections by parasites in the host's natural habitat. The expression of immune priming varies across host and pathogen species, as well as infection routes (oral or wounds), reflecting finely tuned evolutionary adjustments. Evidence from the mealworm beetle (Tenebrio molitor) suggests that Gram-positive bacterial pathogens play a significant role in immune priming after systemic infection. Despite the likelihood of oral infections by natural bacterial pathogens in T. molitor, it remains debated whether ingestion of contaminated food leads to systemic infection, and whether oral immune priming is possible is currently unknown. We first attempted to induce immune priming in both T. molitor larvae and adults by exposing them to food contaminated with living or dead Gram-positive and Gram-negative bacterial pathogens. We found that oral ingestion of living bacteria did not kill them, but septic wounds caused rapid mortality. Intriguingly, the consumption of either dead or living bacteria did not protect against reinfection, contrasting with injury-induced priming. We further examined the effects of infecting food with various living bacterial pathogens on variables such as food consumption, mass gain, and feces production in larvae. We found that larvae exposed to Gram-positive bacteria in their food ingested less food, gained less mass and/or produced more feces than larvae exposed to contaminated food with Gram-negative bacteria or control food. This suggests that oral contamination with Gram-positive bacteria induced both behavioral responses and peristalsis defense mechanisms, even though no immune priming was observed here. Considering that the oral route of infection neither caused the death of the insects nor induced priming, we propose that immune priming in T. molitor may have primarily evolved as a response to the infection risk associated with wounds rather than oral ingestion.

The costs of transgenerational immune priming for homologous and heterologous infections with different serotypes of dengue virus in Aedes aegypti mosquitoes

The immune system is a network of molecules, signaling pathways, transcription, and effector modulation that controls, mitigates, or eradicates agents that may affect the integrity of the host. In mosquitoes, the innate immune system is highly efficient at combating foreign organisms but has the capacity to tolerate vector-borne diseases. These implications lead to replication, dissemination, and ultimately the transmission of pathogenic organisms when feeding on a host. In recent years, it has been discovered that the innate immune response of mosquitoes can trigger an enhanced immunity response to the stimulus of a previously encountered pathogen. This phenomenon, called immune priming, is characterized by a molecular response that prevents the replication of viruses, parasites, or bacteria in the body. It has been documented that immune priming can be stimulated through homologous organisms or molecules, although it has also been documented that closely related pathogens can generate an enhanced immune response to a second stimulus with a related organism. However, the cost involved in this immune response has not been characterized through the transmission of the immunological experience from parents to offspring by transgenerational immune priming (TGIP) in mosquitoes. Here, we address the impact on the rates of oviposition, hatching, development, and immune response in Aedes aegypti mosquitoes, the mothers of which were stimulated with dengue virus serotypes 2 and/or 4, having found a cost of TGIP on the development time of the progeny of mothers with heterologous infections, with respect to mothers with homologous infections. Our results showed a significant effect on the sex ratio, with females being more abundant than males. We found a decrease in transcripts of the siRNA pathway in daughters of mothers who had been exposed to an immune challenge with DV. Our research demonstrates that there are costs and benefits associated with TGIP in Aedes aegypti mosquitoes exposed to DV. Specifically, priming results in a lower viral load in the offspring of mothers who have previously been infected with the virus. Although some results from tests of two dengue virus serotypes show similarities, such as the percentage of pupae emergence, there are differences in the percentage of adult emergence, indicating differences in TGIP costs even within the same virus with different serotypes. This finding has crucial implications in the context of dengue virus transmission in endemic areas where multiple serotypes circulate simultaneously.

Trans-generational immune priming is not mediated by the sex of the parent primed: a meta-analysis of invertebrate data

Traditionally, only vertebrates were thought capable of acquired immune responses, such as the ability to transfer immunological experience vertically to their offspring (known as trans-generational immune priming, TGIP). Increasing evidence challenges this belief and it is now clear that invertebrates also have the ability to exhibit functionally equivalent TGIP. This has led to a surge in papers exploring invertebrate TGIP, with most focusing on the costs, benefits or factors that affect the evolution of this trait. Whilst many studies have found support for the phenomenon, not all studies do, and there is considerable variation in the strength of positive results. To address this, we conducted a meta-analysis to answer the question: what is the overall effect of TGIP in invertebrates? Then, to understand the specific factors that affect its presence and intensity, we conducted a moderator analysis. Our results corroborate that TGIP occurs in invertebrates (demonstrated by a large, positive effect size). The strength of the positive effect was related to if and how offspring were immune challenged (i.e. whether they were challenged with the same or different insult as their parents or not challenged at all). Interestingly, there was no effect of the ecology or life history of the species or the sex of the parent or the offspring primed, and responses were comparable across different immune elicitors. Our publication bias testing suggests that the literature may suffer from some level of positive-result bias. However, even after accounting for potential bias, our effect size remains positive. Publication bias testing can be influenced by diversity in the data set, which was considerable in our data, even after moderator analysis. It is therefore conceivable that differences among studies could be caused by other moderators that were unable to be included in our meta-analysis. Nonetheless, our results suggest that TGIP does occur in invertebrates, whilst providing some potential avenues to examine the factors that account for variation in effect sizes.

Genetic dissection of innate immune memory in Drosophila melanogaster

Current studies have demonstrated that innate immunity possesses memory characteristics. Although the molecular mechanisms underlying innate immune memory have been addressed by numerous studies, genetic variations in innate immune memory and the associated genes remain unclear. Here, we explored innate immune memory in 163 lines of Drosophila melanogaster from the Drosophila Synthetic Population Resource. In our assay system, prior training with low pathogenic bacteria (Micrococcus luteus) increased the survival rate of flies after subsequent challenge with highly pathogenic bacteria (Staphylococcus aureus). This positive training effect was observed in most lines, but some lines exhibited negative training effects. Survival rates under training and control conditions were poorly correlated, suggesting that distinct genetic factors regulate training effects and normal immune responses. Subsequent quantitative trait loci analysis suggested that four loci containing 80 genes may be involved in regulating innate immune memory. Among them, Adgf-A, which encodes an extracellular adenosine deaminase-related growth factor, was shown to be associated with training effects. Our study findings help to elucidate the genetic architecture of innate immune memory in Drosophila and may provide insight for new therapeutic treatments aimed at boosting immunity.

Trained immunity against diseases in domestic animals

Trained immunity is a biological concept that has been demonstrated in different animal species, including human beings. Evidences indicate that innate immune cells can be trained and have a "memory". Under this concept, studies have shown that a first stimulus can potentiate immune responses upon a second one or protect upon homologous or heterologous pathogenic challenges. Research progress on trained innate immunity in mouse models and human beings has provided key information of this phenomenon. In domestic animals, this concept offers a heterologous protection against diseases. Recent studies in domestic animals have demonstrated that trained immunity is induced even by mucosal routes rather than only parenteral routes, as previously evidenced in mice and humans. This situation has led to a major breakthrough in the biotechnology field. Remarkably, the recent first proof-of-concept in calves and goats provides a reality beyond trained immunity as an affordable immunobiotechnological approach to control diseases. Currently, several responses to questions that have been deciphered in mouse and humans seem different in domestic animals; even these differences have been observed among animal species and breeds, which open new questions and challenges. The information of mechanistic studies in domestic animals based on the trained immunity paradigm has not been integrated before; therefore, it needs to be discussed and accurately presented. Moreover, prospects should be defined and biotechnological perspectives provided to promote research and development (R&D) to become a near reality in domestic animal, so this is the main objective of the review.

Current knowledge of immune priming in invertebrates, emphasizing studies on Tenebrio molitor

Vertebrates rely on the most sophisticated adaptive immunity to defend themselves against various pathogens. This includes immunologic memory cells, which mount a stronger and more effective immune response against an antigen after its first encounter. Unlike vertebrates, invertebrates' defense completely depends on the innate immunity mechanisms including humoral and cell-mediated immunity. Furthermore, the invertebrate equivalent of the memory cells was discovered only recently. Since the discovery of transgenerational immune priming (TGIP) in crustaceans, numerous findings have proven the IP in invertebrate classes such as insects. TGIP can be induced through maternal priming pathways such as transcriptional regulation of antimicrobial peptides, and also paternal IP including the induction of proPO system activity. We appraise the diversity and specificity of IP agents to provide sustained immunologic memory in insects, particularly T. molitor in the review. An understanding of IP (more so TGIP) response in T. molitor will deepen our knowledge of invertebrate immunity, and boost the mass-rearing industry by reducing pathogen infection rates.

Current understanding of immune priming phenomena in insects

It may seem that the most important issues related to insect immunity have already been described. However, novel phenomena observed in recent years shed new light on the understanding of the immune response in insects.The adaptive abilities of insects helped them to populate all ecological land niches.One important adaptive ability of insects that facilitates their success is the plasticity of their immune system. Although they only have innate immune mechanisms, insects can increase their resistance after the first encounter with the pathogen. In recent years, this phenomenon,namedimmunepriming, has become a "hot topic" in immunobiology.Priming can occur within or across generations. In the first case, the resistance of a given individual can increase after surviving a previous infection. Transstadial immune priming occurs when infection takes place at one of the initial developmental stages and increased resistance is observed at the pupal or imago stages. Priming across generations (transgenerationalimmune priming, TGIP) relies on the increased resistance of the offspring when one or both parents are infected during their lifetime.Despite the attention that immune priming has received, basic questions remain to be answered, such as regulation of immune priming at the molecular level. Research indicates that pathogen recognition receptors (PRRs) can be involved in the priming phenomenon. Recent studies have highlighted the special role of microRNAs and epigenetics, which can influence expression of genes that can be transmitted through generations although they are not encoded in the nucleotide sequence. Considerable amounts of research are required to fully understand the mechanisms that regulate priming phenomena. The aim of our work is to analyse thoroughly the most important information on immune priming in insects and help raise pertinent questions such that a greater understanding of this phenomenon can be obtained in the future.

A parental transcriptional response to microsporidia infection induces inherited immunity in offspring

Parental infection can result in the production of offspring with enhanced immunity phenotypes. Critically, the mechanisms underlying inherited immunity are poorly understood. Here, we show that Caenorhabditis elegans infected with the intracellular microsporidian parasite N. parisii produce progeny that are resistant to microsporidia infection. We determine the kinetics of the response and show that intergenerational immunity prevents host-cell invasion by Nematocida parisii and enhances survival to the bacterial pathogen Pseudomonas aeruginosa We demonstrate that immunity is induced by the parental transcriptional response to infection, which can be mimicked through maternal somatic depletion of PALS-22 and the retinoblastoma protein ortholog, LIN-35. We find that other biotic and abiotic stresses (viral infection and cadmium exposure) that induce a similar transcriptional response as microsporidia also induce immunity in progeny. Together, our results reveal how a parental transcriptional signal can be induced by distinct stimuli and protect offspring against multiple classes of pathogens.

Recombinant viral proteins delivered orally through inactivated bacterial cells induce protection in Macrobrachium rosenbergii (de Man) against White Tail Disease

White tail disease (WTD) is a disease of Macrobrachium rosenbergii caused by Macrobrachium rosenbergii nodavirus (MrNV) and extra small virus (XSV) with the potential to devastate the aquaculture industry. The present study aimed to explore the possible protection of M. rosenbergii against the disease by oral administration of bacterially expressed recombinant capsid proteins of MrNV and XSV. Juvenile M. rosenbergii were fed with the feed coated with inactivated bacteria encapsulated expressed recombinant viral proteins either individually or in combination for 7 days. Challenge studies using WTD causing agents were carried out after 3 (group I), 10 (group II) and 20 (group III) days post-feeding of viral proteins. Recombinant capsid protein of MrNV showed better protection when compared to other treatments with relative per cent survival of 62.5% (group I), 57.9% (group II) and 39.5% (group III). Treatment controls of groups I, II and III showed 100%, 95% and 95% mortality, respectively. The study demonstrates that oral administration of recombinant capsid proteins of MrNV and XSV provides effective protection against WTD in freshwater prawn.

New Insights into IgZ as a Maternal Transfer Ig Contributing to the Early Defense of Fish against Pathogen Infection

IgZ or its equivalent IgT is a newly discovered teleost specific Ig class that is highly specialized in mucosal immunity. However, whether this IgZ/IgT class participates in other biological processes remains unclear. In this study, we unexpectedly discovered that IgZ is highly expressed in zebrafish ovary, accumulates in unfertilized eggs, and is transmitted to offspring from eggs to zygotes. Maternally transferred IgZ in zygotes is found at the outer and inner layers of chorion, perivitelline space, periphery of embryo body, and yolk, providing different lines of defense against pathogen infection. A considerable number of IgZ⁺ B cells are found in ovarian connective tissues distributed between eggs. Moreover, pIgR, the transporter of IgZ, is also expressed in the ovary and colocalizes with IgZ in the zona radiata of eggs. Thus, IgZ is possibly secreted by ovarian IgZ⁺ B cells and transported to eggs through association with pIgR in a paracrine manner. Maternal IgZ in zygotes showed a broad bacteriostatic activity to different microbes examined, and this reactivity can be manipulated by orchestrating desired bacteria in water where parent fish live or immunizing the parent fish through vaccination. These observations suggest that maternal IgZ may represent a group of polyclonal Abs, providing protection against various environmental microbes encountered by a parent fish that were potentially high risk to offspring. To our knowledge, our findings provide novel insights into a previously unrecognized functional role of IgZ/IgT Ig in the maternal transfer of immunity in fish, greatly enriching current knowledge about this ancient Ig class.

Evidence For Long-Lasting Transgenerational Antiviral Immunity in Insects

Transgenerational immune priming (TGIP) allows memory-like immune responses to be transmitted from parents to offspring in many invertebrates. Despite increasing evidence for TGIP in insects, the mechanisms involved in the transfer of information remain largely unknown. Here, we show that Drosophila melanogaster and Aedes aegypti transmit antiviral immunological memory to their progeny that lasts throughout generations. We observe that TGIP, which is virus and sequence specific but RNAi independent, is initiated by a single exposure to disparate RNA viruses and also by inoculation of a fragment of viral double-stranded RNA. The progeny, which inherit a viral DNA that is only a fragment of the viral RNA used to infect the parents, display enriched expression of genes related to chromatin and DNA binding. These findings represent a demonstration of TGIP for RNA viruses in invertebrates, broadly increasing our understanding of the immune response, host genome plasticity, and antiviral memory of the germline.

Cysteine synthases CYSL-1 and CYSL-2 mediate C. elegans heritable adaptation to P. vranovensis infection

Parental exposure to pathogens can prime offspring immunity in diverse organisms. The mechanisms by which this heritable priming occurs are largely unknown. Here we report that the soil bacteria Pseudomonas vranovensis is a natural pathogen of the nematode Caenorhabditis elegans and that parental exposure of animals to P. vranovensis promotes offspring resistance to infection. Furthermore, we demonstrate a multigenerational enhancement of progeny survival when three consecutive generations of animals are exposed to P. vranovensis. By investigating the mechanisms by which animals heritably adapt to P. vranovensis infection, we found that parental infection by P. vranovensis results in increased expression of the cysteine synthases cysl-1 and cysl-2 and the regulator of hypoxia inducible factor rhy-1 in progeny, and that these three genes are required for adaptation to P. vranovensis. These observations establish a CYSL-1, CYSL-2, and RHY-1 dependent mechanism by which animals heritably adapt to infection.

Identification and characterization of a novel L-type lectin (MjLTL2) from kuruma shrimp (Marsupenaeus japonicus)

L-type lectins (LTLs) belong to the lectin family and are characterized by a conserved structural motif in their carbohydrate recognition domain. LTLs are homologous to leguminous lectins. In this study, we identified and functionally characterized an LTL from kuruma shrimp Marsupenaeus japonicus. We designated this LTL as MjLTL2. MjLTL2 contains a signal peptide, a Lectin_leg domain, a coiled coil, and transmembrane domain. MjLTL2 is distributed in hemocytes, heart, hepatopancreas, gill, stomach, and intestine; higher expression levels are seen in hemocytes and the hepatopancreas than in other tissues. MjLTL2 was upregulated following challenge of shrimp with Vibrio anguillarum and white spot syndrome virus (WSSV). MjLTL2 can agglutinate several bacteria without Ca²⁺. In addition, MjLTL2 could bind to several Gram-positive and -negative bacteria by binding to their lipopolysaccharide and peptidoglycan. However, MjLTL2 could not enhance the clearance of V. anguillarum in vivo. In the presence of WSSV infection, MjLTL2 knockdown by RNA interference resulted in a 7-day lower cumulative mortality of M. japonicus. Moreover, less VP19, VP24, VP26, and VP28 mRNAs were extracted from the hemocytes of MjLTL2 knockdown shrimp than from the control. These results suggest that MjLTL2 is involved in immune responses in shrimp.

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.

No evidence of queen immunisation despite transgenerational immunisation in Crematogaster scutellaris ants

Like vertebrates, invertebrates evolved acquired immunity based on memory-like mechanisms, known as immunisation. Immunisation and its transmission among individuals are phylogenetically ancestral and conserved characters that have been reported in different insect orders. Physiological mechanisms are still largely unknown, and the high variability in responses in different host-parasite systems led to different conclusions. In social insect species, the complex organisation of colonies further complicates the interpretation of the immune responses. In ants, it has been shown that the expression of immunisation depends on species, caste and physiological status of individuals. In this study, we investigate the occurrence of immunisation in queens of Crematogaster scutellaris ants using the fungus Metarhizium anisopliae as elicitor. Foundation in C. scutellaris is claustral and monogynic, allowing us to test the existence of the phenomenon in two distinct physiological conditions, corresponding to the claustral and colonial phases of queens. Queens and foundresses challenged with heavy doses of the pathogen showed higher mortality if previously exposed to light doses, indicating the absence of immunisation in our experimental settings. On the other hand, evidence of the trans-generational immunisation in the same host-parasite system has been recently found, where workers produced by queens exposed to light doses of M. anisopliae survived longer than those belonging to the control group. These results indicate that foundresses exposed to M. anisopliae can elicit an increased resistance in the offspring without providing themselves with a similar increased immune response and that immunisation and trans-generational immunisation are uncoupled phenomena in this host-parasite system.

Transgenerational Immune Priming in the Field: Maternal Environmental Experience Leads to Differential Immune Transfer to Oocytes in the Marine Annelid Hediste diversicolor

Transgenerational immune priming (TGIP) is an intriguing form of parental care which leads to the plastic adjustment of the progeny’s immunity according to parental immune experience. Such parental effect has been described in several vertebrate and invertebrate taxa. However, very few empirical studies have been conducted from the field, with natural host-parasite systems and real ecological settings, especially in invertebrates. We investigated TGIP in wild populations of the marine annelid Hediste diversicolor. Females laid eggs in a mud tube and thus shared the local microbial threats with the first developmental stages, thus meeting expectations for the evolution of TGIP. We evidenced that a maternal bacterial challenge led to the higher antibacterial defense of the produced oocytes, with higher efficiency in the case of Gram-positive bacterial challenge, pointing out a prevalent role of these bacteria in the evolutionary history of TGIP in this species. Underlying mechanisms might involve the antimicrobial peptide hedistin that was detected in the cytoplasm of oocytes and whose mRNAs were selectively stored in higher quantity in mature oocytes, after a maternal immune challenge. Finally, maternal immune transfer was significantly inhibited in females living in polluted areas, suggesting associated costs and the possible trade-off with female’s protection.

Resistance against Trichinella spiralis infection in pups delivered by T. spiralis-infected dam

Maternal antibody transmission via placenta and breastmilk are known to confer protection in infants. In this study, we investigated the maternal immunity transmission in pups delivered by rats infected with Trichinella spiralis and assessed the resulting resistance against subsequent parasitic infection. Our results revealed that parasite-specific IgG, IgG1 and IgG2a antibodies were present in pups prior to breastmilk ingestion (pre-milk), in which IgG and IgG1 antibodies persisted until week 8 after birth while parasite-specific IgG2a antibodies only lasted until week 4. After weaning on week 3, pups delivered by T. spiralis-infected dam and subsequently challenge-infected (immune-challenge) were found to possess higher mucosal IgG antibodies than control groups, whereas mucosal IgA levels were not significantly different across all groups. T. spiralis excretory-secretory antigen was discovered to react with pup sera until week 8, correlating with the resistance against parasitic infection which is represented by lessened worm burden. Upon T. spiralis infection at weeks 3 and 8, lower levels of eosinophil responses were detected in immune-challenge pups compared to naïve-challenge pups, indicating correlates of resistances in which ADCC may be involved. Findings from the present study demonstrate that resistances against T. spiralis infection in pups can be acquired by maternally-derived IgG, IgG1 and IgG2a antibody transmission through the placenta and breastmilk from T. spiralis-infected dam, which lasts until week 8.

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.

Trans-generational immunization in the acrobat ant Crematogaster scutellaris

Trans-generational immunization is defined as the transmission of an enhanced resistance to a pathogen from parents to offspring. By using the host-parasite system of the ant Crematogaster scutellaris and the entomopathogenic fungus Metarhizium anisopliae, we describe this phenomenon for the first time in ants. We exposed four groups of hibernating queens to different treatments (i) a non-lethal dose of live conidiospores in Triton, (ii) a dose of heat-killed conidiospores in Triton, (iii) a control Triton solution, and (iv) a naive control. We exposed their first workers to a high dose of conidiospores and measured mortality rates. Workers produced by queens exposed to live conidiospores survived longer than those belonging to the other groups, while exposure to Triton and dead spores had no effect. Starved workers showed a significantly higher mortality. The treatments did not influence queen mortality, nor the number of offspring they produced at the emergence of the first worker, showing no evidence of immunization costs-at least for these parameters in the first year of colony development. We propose that trans-generational immunization represents an important component of social immunity that could affect colony success, particularly during the critical phase of claustral foundation.

Interaction between Insects, Toxins, and Bacteria: Have We Been Wrong So Far?

Toxins are a major virulence factor produced by many pathogenic bacteria. In vertebrates, the response of hosts to the bacteria is inseparable from the response to the toxins, allowing a comprehensive understanding of this tripartite host-pathogen-toxin interaction. However, in invertebrates, this interaction has been investigated by two complementary but historically distinct fields of research: toxinology and immunology. In this article, I highlight how such dichotomy between these two fields led to a biased, or even erroneous view of the ecology and evolution of the interaction between insects, toxins, and bacteria. I focus on the reason behind such a dichotomy, on how to bridge the fields together, and on confounding effects that could bias the outcome of the experiments. Finally, I raise four questions at the border of the two fields on the cross-effects between toxins, bacteria, and spores that have been largely underexplored to promote a more comprehensive view of this interaction.

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.

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.

Evolution of transgenerational immunity in invertebrates

Over a decade ago, the discovery of transgenerational immunity in invertebrates shifted existing paradigms on the lack of sophistication of their immune system. Nonetheless, the prevalence of this trait and the ecological factors driving its evolution in invertebrates remain poorly understood. Here, we develop a theoretical host-parasite model and predict that long lifespan and low dispersal should promote the evolution of transgenerational immunity. We also predict that in species that produce both philopatric and dispersing individuals, it may pay to have a plastic allocation strategy with a higher transgenerational immunity investment in philopatric offspring because they are more likely to encounter locally adapted pathogens. We review all experimental studies published to date, comprising 21 invertebrate species in nine different orders, and we show that, as expected, longevity and dispersal correlate with the transfer of immunity to offspring. The validity of our prediction regarding the plasticity of investment in transgenerational immunity remains to be tested in invertebrates, but also in vertebrate species. We discuss the implications of our work for the study of the evolution of immunity, and we suggest further avenues of research to expand our knowledge of the impact of transgenerational immune protection in host-parasite interactions.

Spatial Epidemiology and Risk Factor Analysis of White Spot Disease in the Shrimp Farming Industry of Sinaloa, Mexico, from 2005 to 2011

White spot disease (WSD), caused by the white spot syndrome virus, is currently one of the primary causes of mortality and economic losses in the shrimp farming industry worldwide. In Mexico, shrimp production is one of the most important primary activities generating an annual income of USD 711 million. However, WSD introduction in 1999 had a devastating impact for the Mexican shrimp industry. The aim of this study was to characterize the WSD spatio-temporal patterns and to identify the primary risk factors contributing to WSD occurrence from 2005 to 2011 in Sinaloa, Mexico. We used data collected by the 'Comité Estatal de Sanidad Acuícola de Sinaloa' from 2005 to 2011 regarding WSD outbreaks as well as environmental, production and husbandry factors at farm level. The spatio-temporal patterns of WSD were described using space-time scan statistics. The effect of 52 variables on the time to WSD outbreak occurrence was assessed using a multivariable Cox proportional hazards model. Results reveal that WSD risk and survival time were not homogeneously distributed as suggested by the significant clusters obtained using the space-time permutation model and the space-time exponential model, respectively. The Cox model revealed that the first production cycle [hazard ratio (HR) = 11.31], changes from 1 to 1.4°C of temperature oscillation caused by 'El Niño'/'La Niña' events (HR = 1.44) and high average daily growths (HR = 1.26) were significantly associated with lower survival (i.e. shorter time to WSD outbreak) on farm. Conversely, shrimp weight at the moment of the outbreak (HR = 0.159), changes from -0.9 to -0.5°C of temperature oscillation caused by 'El Niño'/'La Niña' events (HR = 0.540), high superficial water temperature during the pound stocking (HR = 0.823) and high (>100) number of days of culture (HR = 0.830) were factors associated with higher survival. Results are expected to inform the design of risk-based, intervention strategies to minimize the impact of WSD in Mexico.

Immune memory in invertebrates

Evidence for innate immune memory (or 'priming') in invertebrates has been accumulating over the last years. We here provide an in-depth review of the current state of evidence for immune memory in invertebrates, and in particular take a phylogenetic viewpoint. Invertebrates are a very heterogeneous group of animals and accordingly, evidence for the phenomenon of immune memory as well as the hypothesized molecular underpinnings differ largely for the diverse invertebrate taxa. The majority of research currently focuses on Arthropods, while evidence from many other groups of invertebrates is fragmentary or even lacking. We here concentrate on immune memory that is induced by pathogenic challenges, but also extent our view to a non-pathogenic context, i.e. allograft rejection, which can also show forms of memory and can inform us about general principles of specific self-nonself recognition. We discuss definitions of immune memory and a number of relevant aspects such as the type of antigens used, the route of exposure, and the kinetics of reactions following priming.

Alpha 2 macroglobulin is a maternally-derived immune factor in amphioxus embryos: New evidence for defense roles of maternal immune components in invertebrate chordate

In fish, a series of maternal derived immune components have been identified in their eggs or embryos at very early stages, which are proposed to provide protections to themselves against pathogenic attacks from hostile environment. The phenomenon of maternal immunity has been also recorded in several invertebrate species, however, so far, very limited information about the maternal immune molecules are available. In this study, it was demonstrated maternal alpha2 macroglobulin (A2m) protein, an important innate immune factor, exists in the fertilized eggs of amphioxus Branchiostoma japonicum, an invertebrate chordate. Maternal mRNA of A2m was also detected in amphioxus embryos at very early developing stages. In addition, it was recorded that the egg lysate prepared from the newly fertilized eggs can inhibit the growth of both Gram-negative bacterium Escherichia coli and Gram-positive bacterium Staphylococcus aureus in a concentration dependent manner. The bacteriostatic activity can be reduced notably after precipitated A2m with anti-A2m antibody. Thus maternal A2m is partly attributed to the bacteriostatic activity. It was further demonstrated that recombinant A2m can bind to E. coli cells directly. All these points come to a result that A2m is a maternal immune factor existing in eggs of invertebrate chordate, which may be involved in defense their embryos against harmful microbes' attacks.

Epigenetic alterations and decreasing insecticide sensitivity of the Asian tiger mosquito Aedes albopictus

A range of environmental factors, including chemicals, can affect epigenetic processes in organisms leading to variations in phenotype. Thus, epigenetics displays an important environmentally responsive element. The transgenerational impact of environmental stressors on DNA methylation and phenotype was the focus of this study. The influence of two known DNA methylation-changing agents, the phytoestrogen genistein and the fungicide vinclozolin, on the overall DNA methylation level in the Asian tiger mosquito Aedes albopictus was investigated. The experiment comprised four generations in a full life-cycle design with an exposed parental generation and three consecutive non-exposed offspring generations. Application of the methylation agents to the parental generation of the study led to an alteration of the global DNA methylation level of the exposed individuals and those in two subsequent generations. The phenotypic variability of the offspring generations was assessed by examining their insecticide sensitivity. Here, a significant decrease in sensitivity (p<0.01) towards the model insecticide imidacloprid revealed alterations of the mosquito's phenotype in two subsequent generations. Thus, the evaluation of A. albopictus from an epigenetic perspective can contribute important information to the study of the high adaptability of this invasive disease vector to new environments, and its underlying mechanisms.

Trans-generational Immune Priming Protects the Eggs Only against Gram-Positive Bacteria in the Mealworm Beetle

In many vertebrates and invertebrates, offspring whose mothers have been exposed to pathogens can exhibit increased levels of immune activity and/or increased survival to infection. Such phenomena, called "Trans-generational immune priming" (TGIP) are expected to provide immune protection to the offspring. As the offspring and their mother may share the same environment, and consequently similar microbial threats, we expect the immune molecules present in the progeny to be specific to the microbes that immune challenged the mother. We provide evidence in the mealworm beetle Tenebrio molitor that the antimicrobial activity found in the eggs is only active against Gram-positive bacteria, even when females were exposed to Gram-negative bacteria or fungi. Fungi were weak inducers of TGIP while we obtained similar levels of anti-Gram-positive activity using different bacteria for the maternal challenge. Furthermore, we have identified an antibacterial peptide from the defensin family, the tenecin 1, which spectrum of activity is exclusively directed toward Gram-positive bacteria as potential contributor to this antimicrobial activity. We conclude that maternal transfer of antimicrobial activity in the eggs of T. molitor might have evolved from persistent Gram-positive bacterial pathogens between insect generations.

Maternal Exposure of a Beetle to Pathogens Protects Offspring against Fungal Disease

Maternal exposure to an immune challenge can convey enhanced immunity to invertebrate offspring in the next generation. We investigated whether maternal exposure of the Asian longhorned beetle, Anoplophora glabripennis, to two species of the fungus Metarhizium or the bacterium Serratia marcescens elicited transgenerational immune priming (TGIP). We tested specificity of this protection and whether occurrence of TGIP was dependent on maternal exposure to living versus dead pathogens. Our results show that TGIP occurred and protected offspring against Metarhizium brunneum. Maternal exposure to S. marcescens provided non-specific protection to offspring against a fungal pathogen, but TGIP in response to Metarhizium only occurred when offspring were exposed to the same fungal species that was used to prime mothers. Moreover, TGIP in response to M. brunneum occurred only after maternal exposure to living rather than dead fungus. Our findings suggest that occurrence of TGIP could be both specific and dependent on whether the pathogen was alive.

Reprint of "evolution of specific immunity in shrimp - a vaccination perspective against white spot syndrome virus"

Invertebrates lack true adaptive immunity and it solely depends on the primitive immunity called innate immunity. However, various innate immune molecules and mechanisms are identified in shrimp that plays potential role against invading bacterial, fungal and viral pathogens. Perceiving the shrimp innate immune mechanisms will contribute in developing effective vaccine strategies against major shrimp pathogens. Hence this review intends to explore the innate immune molecules of shrimp with suitable experimental evidences together with the evolution of "specific immune priming" of invertebrates. In addition, we have emphasized on the development of an effective vaccine strategy against major shrimp pathogen, white spot syndrome virus (WSSV). The baculovirus displayed rVP28 (Bac-VP28), a major envelope protein of WSSV was utilized to study its vaccine efficacy by oral route. A significant advantage of this baculovirus expression cassette is the use of WSSV-immediate early 1 (ie1) promoter that derived the abundant expression of rVP28 protein at the early stage of the infection in insect cell. The orally vaccinated shrimp with Bac-VP28 transduced successfully in the shrimp cells as well as provided highest survival rate. In support to our vaccine efficacy we analysed Pattern Recognition Proteins (PRPs) β-1,3 glucan lipopolysaccharides (LGBP) and STAT gene profiles in the experimental shrimp. Indeed, the vaccination of shrimp with Bac-VP28 demonstrated some degree of specificity with enhanced survival rate when compared to control vaccination with Bac-wt. Hence it is presumed that the concept of "specific immune priming" in relevant to shrimp immunity is possible but may not be common to all shrimp pathogens.

Maternal immune transfer in mollusc

Maternal immunity refers to the immunity transferred from mother to offspring via egg, playing an important role in protecting the offspring at early life stages and contributing a trans-generational effect on offspring's phenotype. Because fertilization is external in most of the molluscs, oocytes and early embryos are directly exposed to pathogens in the seawater, and thus maternal immunity could provide a better protection before full maturation of their immunological systems. Several innate immune factors including pattern recognition receptors (PRRs) like lectins, and immune effectors like lysozyme, lipopolysaccharide binding protein/bacterial permeability-increasing proteins (LBP/BPI) and antioxidant enzymes have been identified as maternally derived immune factors in mollusc eggs. Among these immune factors, some maternally derived lectins and antibacterial factors have been proved to endue mollusc eggs with effective defense ability against pathogen infection, while the roles of other factors still remain untested. The physiological condition of mollusc broodstock has a profound effect on their offspring fitness. Many other factors such as nutrients, pathogens, environment conditions and pollutants could exert considerable influence on the maternal transfer of immunity. The parent molluscs which have encountered an immune stimulation endow their offspring with a trans-generational immune capability to protect them against infections effectively. The knowledge on maternal transfer of immunity and the trans-generational immune effect could provide us with an ideal management strategy of mollusc broodstock to improve the immunity of offspring and to establish a disease-resistant family for a long-term improvement of cultured stocks.

Evolution of specific immunity in shrimp - a vaccination perspective against white spot syndrome virus

Invertebrates lack true adaptive immunity and it solely depends on the primitive immunity called innate immunity. However, various innate immune molecules and mechanisms are identified in shrimp that plays potential role against invading bacterial, fungal and viral pathogens. Perceiving the shrimp innate immune mechanisms will contribute in developing effective vaccine strategies against major shrimp pathogens. Hence this review intends to explore the innate immune molecules of shrimp with suitable experimental evidences together with the evolution of "specific immune priming" of invertebrates. In addition, we have emphasized on the development of an effective vaccine strategy against major shrimp pathogen, white spot syndrome virus (WSSV). The baculovirus displayed rVP28 (Bac-VP28), a major envelope protein of WSSV was utilized to study its vaccine efficacy by oral route. A significant advantage of this baculovirus expression cassette is the use of WSSV-immediate early 1 (ie1) promoter that derived the abundant expression of rVP28 protein at the early stage of the infection in insect cell. The orally vaccinated shrimp with Bac-VP28 transduced successfully in the shrimp cells as well as provided highest survival rate. In support to our vaccine efficacy we analysed Pattern Recognition Proteins (PRPs) β-1,3 glucan lipopolysaccharides (LGBP) and STAT gene profiles in the experimental shrimp. Indeed, the vaccination of shrimp with Bac-VP28 demonstrated some degree of specificity with enhanced survival rate when compared to control vaccination with Bac-wt. Hence it is presumed that the concept of "specific immune priming" in relevant to shrimp immunity is possible but may not be common to all shrimp pathogens.

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.

Beta-glucan: an ideal immunostimulant in aquaculture (a review)

The major hindrance in the development and sustainability of aquaculture industry is the occurrence of various diseases in the farming systems. Today, preventive and management measures are central concern to overcome such outbreak of diseases. Immunostimulants are considered as an effective tool for enhancing immune status of cultured organisms. Among different immunostimulants used in aquaculture practices, β-glucan is one of the promising immunostimulant, which is a homopolysaccharide of glucose molecule linked by the glycoside bond. It forms the major constituents of cell wall of some plants, fungi, bacteria, mushroom, yeast, and seaweeds. Major attention on β-glucan was captivated with the gain in knowledge on its receptors and the mechanism of action. The receptor present inside the animal body recognizes and binds to β-glucan, which in turn renders the animal with high resistance and enhanced immune response. This review highlights β-glucan as an immunostimulant, its effective dosages, and route of administration and furthermore provides an outline on role of β-glucan in enhancing growth, survival, and protection against infectious pathogens pertaining to fishes and shellfishes. Study also summarizes the effect of β-glucan on its receptors, recognition of proteins, immune-related enzymes, immune-related gene expression and their mechanisms of action.

Maternal immunity in fish

Both innate and adaptive immune-relevant factors are transferred from mother to offspring in fishes. These maternally-transferred factors include IgM, lysozymes, lectin, cathelicidin and complement components. Recently, yolk proteins, phosvitin and lipovitellin, have been shown to be maternally-transferred factors, functioning in the defense of teleost larvae against pathogens. Among these factors, the mode of action of complement components and yolk proteins has been explored, whereas that of all the other factors remains elusive. At present, the transfer mechanisms of maternally-derived immune factors are largely unknown although those of IgM and yolk protein transmission from mother to offspring have been reported in some fishes. Maternal transfer of immunity is affected by many elements, including biological factors, such as age and maturation, and environmental conditions experienced by brood fish, such as pathogens and nutritional supply. Practically, the manipulation of maternal immunity transfer can be used to enhance the survival rate of fish larvae.

Relationship between maternal transfer of immunity and mother fecundity in an insect

Trans-generational immune priming (TGIP) corresponds to the plastic adjustment of offspring immunity as a result of maternal immune experience. TGIP is expected to improve mother's fitness by improving offspring individual performance in an environment where parasitism becomes more prevalent. However, it was recently demonstrated that maternal transfer of immunity to the offspring is costly for immune-challenged female insects. Thus, these females might not provide immune protection to all their offspring because of the inherent cost of other fitness-related traits. Females are therefore expected to adjust their investment to individual offspring immune protection in ways that maximize their fitness. In this study, we investigated how bacterially immune-challenged females of the mealworm beetle, Tenebrio molitor, provision their eggs with immune protection according to egg production. We found that immune-challenged females provide a variable number of their eggs with internal antibacterial activity along egg-laying bouts. Furthermore, within the first immune-protected egg-laying bout (2-4 days after the maternal immune challenge), the number of eggs protected was strongly dependent on the number of eggs produced. Immune-challenged females might therefore adjust their investment into TGIP and fecundity according of their individual perception of the risk of dying from the infection and the expected parasitic conditions for the offspring.

Maternal environment shapes the life history and susceptibility to malaria of Anopheles gambiae mosquitoes

BACKGROUND

It is becoming generally recognized that an individual's phenotype can be shaped not only by its own genotype and environmental experience, but also by its mother's environment and condition. Maternal environmental factors can influence mosquitoes' population dynamics and susceptibility to malaria, and therefore directly and indirectly the epidemiology of malaria.

METHODS

In a full factorial experiment, the effects of two environmental stressors - food availability and infection with the microsporidian parasite Vavraia culicis - of female mosquitoes (Anopheles gambiae sensu stricto) on their offspring's development, survival and susceptibility to malaria were studied.

RESULTS

The offspring of A. gambiae s.s. mothers infected with V. culicis developed into adults more slowly than those of uninfected mothers. This effect was exacerbated when mothers were reared on low food. Maternal food availability had no effect on the survival of their offspring up to emergence, and microsporidian infection decreased survival only slightly. Low food availability for mothers increased and V. culicis-infection of mothers decreased the likelihood that the offspring fed on malaria-infected blood harboured malaria parasites (but neither maternal treatment influenced their survival up to dissection).

CONCLUSIONS

Resource availability and infection with V. culicis of A. gambiae s.s. mosquitoes not only acted as direct environmental stimuli for changes in the success of one generation, but could also lead to maternal effects. Maternal V. culicis infection could make offspring more resistant and less likely to transmit malaria, thus enhancing the efficacy of the microsporidian for the biological control of malaria.

Microarray analyses of shrimp immune responses

Shrimp aquaculture is one of the major foodproducing industries in the world. However, it is being impacted by several problems including diseases, antibiotic use, and environmental factors. The extent of the effects of these problems in the immune system of the shrimp at the molecular level is just beginning to be understood. Here, we review the gene expression profile of shrimp in response to some of these problems using the high-throughput microarray analysis, including white spot syndrome virus, yellow head virus, Vibrio spp., peptidoglycan, oxytetracycline, oxolinic acid, salinity, and temperature.

Induction and transmission of tolerance to the synthetic pesticide emamectin benzoate in field and laboratory populations of diamondback moth

Field surveys of pest insect pest populations in agroecosystems reveal low but significant levels of tolerance to synthetic and biological pesticides but fail to uncover resistance alleles in test crosses. To study the potential of inducible mechanisms to generate tolerance to synthetic pesticides, we performed baseline susceptibility studies in field and laboratory populations of diamondback moth, Plutella xylostella (L.), to commercial formulations of emamectin benzoate. Pesticide exposure in the field caused elevated levels of tolerance, which decreased in field-collected populations after maintaining insects with pesticide-free diet in the laboratory. Because no significant resistance alleles were identified in back-crossed individuals, the observed increase in tolerance was probably not based on preexisting recessive resistance mechanisms in the population. Instead, the genetic analysis after five and 12 generations is compatible with a transient up-regulation of an immune and metabolic status in tolerant insects that can be transmitted to offspring by a maternal effect. Although the epigenetic effects contributed to incremental increases in tolerance in the first five generations, other resistance mechanisms that are transmitted genetically predominate after 12 generations of increased exposure to the pesticide.

Poor maternal environment enhances offspring disease resistance in an invertebrate

Natural populations vary tremendously in their susceptibility to infectious disease agents. The factors (environmental or genetic) that underlie this variation determine the impact of disease on host population dynamics and evolution, and affect our capacity to contain disease outbreaks and to enhance resistance in agricultural animals and disease vectors. Here, we show that changes in the environmental conditions under which female Daphnia magna are kept can more than halve the susceptibility of their offspring to bacterial infection. Counter-intuitively, and unlike the effects typically observed in vertebrates for transfer of immunity, mothers producing offspring under poor conditions produced more resistant offspring than did mothers producing offspring in favourable conditions. This effect occurred when mothers who were well provisioned during their own development then found themselves reproducing in poor conditions. These effects likely reflect adaptive optimal resource allocation where better quality offspring are produced in poor environments to enhance survival. Maternal exposure to parasites also reduced offspring susceptibility, depending on host genotype and offspring food levels. These maternal responses to environmental conditions mean that studies focused on a single generation, and those in which environmental variation is experimentally minimized, may fail to describe the crucial parameters that influence the spread of disease. The large maternal effects we report here will, if they are widespread in nature, affect disease dynamics, the level of genetic polymorphism in populations, and likely weaken the evolutionary response to parasite-mediated selection.