Parental investment and immune dynamics in sex-role reversed pipefishes

Parental care elevates reproductive success by allocating resources into the upbringing of the offspring. However, it also imposes strong costs for the care-giving parent and can foster sexual dimorphism. Trade-offs between the reproductive system and the immune system may result in differential immunological capacities between the care-providing and the non-care-providing parent. Usually, providing care is restricted to the female sex making it impossible to study a sex-independent influence of parental investment on sexual immune dimorphism. The decoupling of sex-dependent parental investment and their influences on the parental immunological capacity, however, is possible in syngnathids, which evolved the unique male pregnancy on a gradient ranging from a simple carrying of eggs on the trunk (Nerophinae, low paternal investment) to full internal pregnancy (Syngnathus, high paternal investment). In this study, we compared candidate gene expression between females and males of different gravity stages in three species of syngnathids (Syngnathus typhle, Syngnathus rostellatus and Nerophis ophidion) with different male pregnancy intensities to determine how parental investment influences sexual immune dimorphism. While our data failed to detect sexual immune dimorphism in the subset of candidate genes assessed, we show a parental care specific resource-allocation trade-off between investment into pregnancy and immune defense when parental care is provided

A summer heat wave decreases the immunocompetence of the mesograzer, Idotea baltica

Extreme events associated with global change will impose increasing stress on coastal organisms. How strong biological interactions such as the host-parasite arms-race are modulated by environmental change is largely unknown. The immune system of invertebrates, in particular phagocytosis and phenoloxidase activity response are key defence mechanisms against parasites, yet they may be sensitive to environmental perturbations. We here simulated an extreme event that mimicked the European heat wave in 2003 to investigate the effect of environmental change on the immunocompetence of the mesograzer Idotea baltica. Unlike earlier studies, our experiment aimed at simulation of the natural situation as closely as possible by using long acclimation, a slow increase in temperature and a natural community setting including the animals' providence with natural food sources (Zostera marina and Fucus vesiculosus). Our results demonstrate that a simulated heat wave results in decreased immunocompetence of the mesograzer Idotea baltica, in particular a drop of phagocytosis by 50%. This suggests that global change has the potential to significantly affect host-parasite interaction

Selection by higher-order effects of salinity and bacteria on early life-stages of Western Baltic spring-spawning herring

Habitat stratification by abiotic and biotic factors initiates divergence of populations and leads to ecological speciation. In contrast to fully marine waters, the Baltic Sea is stratified by a salinity gradient that strongly affects fish physiology, distribution, diversity and virulence of important marine pathogens. Animals thus face the challenge to simultaneously adapt to the concurrent salinity and cope with the selection imposed by the changing pathogenic virulence. Western Baltic spring-spawning herring (Clupea harengus) migrate to spawning grounds characterized by different salinities to which herring are supposedly adapted. We hypothesized that herring populations do not only have to cope with different salinity levels but that they are simultaneously exposed to higher-order effects that accompany the shifts in salinity, that is induced pathogenicity of Vibrio bacteria in lower saline waters. To experimentally evaluate this, adults of two populations were caught in their spawning grounds and fully reciprocally crossed within and between populations. Larvae were reared at three salinity levels, representing the spawning ground salinity of each of the two populations, or Atlantic salinity conditions resembling the phylogenetic origin of Clupea harengus. In addition, larvae were exposed to a Vibrio spp. infection. Life-history traits and gene expression analysis served as response variables. Herring seem adapted to Baltic Sea conditions and cope better with low saline waters. However, upon a bacterial infection, herring larvae suffer more when kept at lower salinities implying reduced resistance against Vibrio or higher Vibrio virulence. In the context of recent climate change with less saline marine waters in the Baltic Sea, such interactions may constitute key future stressors

Immune-Related Functions of the Hivep Gene Family in East African Cichlid Fishes

Immune-related genes are often characterized by adaptive protein evolution. Selection on immune genes can be particularly strong when hosts encounter novel parasites, for instance, after the colonization of a new habitat or upon the exploitation of vacant ecological niches in an adaptive radiation. We examined a set of new candidate immune genes in East African cichlid fishes. More specifically, we studied the signatures of selection in five paralogs of the human immunodeficiency virus type I enhancer-binding protein (Hivep) gene family, tested their involvement in the immune defense, and related our results to explosive speciation and adaptive radiation events in cichlids. We found signatures of long-term positive selection in four Hivep paralogs and lineage-specific positive selection in Hivep3b in two radiating cichlid lineages. Exposure of the cichlid Astatotilapia burtoni to a vaccination with Vibrio anguillarum bacteria resulted in a positive correlation between immune response parameters and expression levels of three Hivep loci. This work provides the first evidence for a role of Hivep paralogs in teleost immune defense and links the signatures of positive selection to host-pathogen interactions within an adaptive radiation

Parental investment matters for maternal and offspring immune defense in the mouthbrooding cichlid Astatotilapia burtoni

Background: Parental care, while increasing parental fitness through offspring survival, also bears cost to the care-giving parent. Consequentially, trade offs between parental care and other vitally important traits, such as the immune system seem evident. In co-occurring phases of parental care and immunological challenges negative consequences through a resource allocation trade off on both the parental and the offspring conditions can be predicted. While the immune system reflects parental stress conditions, parental immunological investments also boost offspring survival via the transfer of immunological substances (trans-generational immune priming). We investigated this relationship in the mouthbrooding East African cichlid Astotatilapia burtoni. Prior to mating, females were exposed to an immunological activation, while others remained immunologically naïve. Correspondingly, the immunological status of females was either examined directly after reproduction or after mouthbrooding had ceased. Offspring from both groups were exposed to immunological challenges to assess the extent of trans-generational immune priming. As proxy for immune status, cellular immunological activity and gene expression were determined. Results: Both reproducing and mouthbrooding females allocate their resources towards reproduction. While upon reproduction the innate immune system was impeded, mouthbrooding females showed an attenuation of inflammatory components. Juveniles from immune challenged mouthbrooding females showed downregulation of immune and life history candidate genes, implying a limitation of trans-generational plasticity when parents experience stress during the costly reproductive phase. Conclusion: Our results provide evidence that both parental investment via mouthbrooding and the rise of the immunological activity upon an immune challenge are costly traits. If applied simultaneously, not only mothers seem to be impacted in their performance, but also offspring are impeded in their ability to react upon a potentially virulent pathogen exposure

Immune stimulation in European sea bass (Dicentrarchus labrax) larvae by administration of Poly-ß-hydroxybutyrate (PHB)

Global aquaculture production is growing rapidly, however, the industry is facing great challenges such as high mortality rates during early life stages. The lack of a fully mature immune system makes larvae highly sensitive to infectious diseases. One of the most common pathogenic bacteria in larviculture is Vibrio anguillarum causing worldwide severe economic losses. Due to the development of antibiotic resistances, the establishment of alternative methods to prevent and control diseases, ensure efficient growth and reach maximal survival rates is mandatory to optimize aquaculture productivity. A promising solution might be the early activation of the immature immune system of fish larvae by administration of immunostimulants as nutritional supplements. In our study we assessed the potential immunomodulatory effect of poly-ß-hydroxybutyrate (PHB) in European sea bass (Dicentrarchus labrax) larvae. PHB is a bacterial energy storage compound which may have a potential application as an immunostimulant in fish culture. In our experiment we used rotifers as live carriers to feed PHB-accumulating bacteria (Alcaligenes eutrophus) to first-feeding European sea bass larvae over a period of 14 days. To estimate the immediate impact of PHB, larval mortality rates were monitored daily during the course of the experiment. In order to assess the disease resistance of the larvae, survival rates after bath challenge with Vibrio anguillarum after 3 and 14 days of PHB treatment and 7 days post PHB treatment were monitored. Furthermore, we determined gene expression profiles for immune genes as well as metabolism- and stress-related genes. Results will be discussed in respect to the use of PHB in fish hatcheries and its effect on the immune system of first feeding sea bass

Does poly-ß-hydroxybutyrate stimulate the immune system of European sea bass larvae?

Introduction Various probiotics and immunostimulants have been shown to enhance the immune response and alter the disease resistance of aquaculture organisms. The bacterial energy storage compound poly-ß-hydroxybutyrate (PHB) for example improves resistance against pathogenic infections in shrimp (Laranja et al., 2014) and exhibits a controlling effect on the gut microbiota of juvenile sea bass which may result in the stimulation of immune functions (De Schryver et al., 2011). These properties might be of special importance for culturing early life stages since their immune system is not yet fully developed. Therefore, we assessed the potential immunostimulating effect of PHB in European sea bass (Dicentrarchus labrax) larvae in our study. Materials and methods We used rotifers as live carriers to feed PHB-accumulating bacteria (Alcaligenes eutrophus) to first-feeding larvae over a period of 14 days. Bacteria with a low (2.5%) and a high (75%) PHB content were used, respectively. Apart from the dose effect, we wanted to determine to which extend the point in time of the PHB administration matters. Therefore, PHB was added (in some experimental groups) directly to the water from the moment of mouth opening onwards. This led to the following experimental groups: 1) early and 2) later stimulation with a low PHB level, 3) early and 4) later stimulation with a high PHB level and 5) a control without any PHB. To estimate the immediate impact of PHB, larval mortality rates were monitored daily over the course of the experiment. Furthermore, larvae were sampled the first time after being fed for 3 days with PHB encapsulated in rotifers (and 5 days of PHB water treatment) and the second time after 14 days PHB via rotifers (and 16 days of PHB water treatment), respectively. Results and discussion Larval mortality rates were found to be the highest in the control group. During both sampling points larvae were slightly smaller and weighed less in the control group. The analysis of the gene expression profiles revealed that only certain immune genes such as cytokines (Interleukin-1ß, Interleukin 8 and TNFα) were affected by the PHB treatment. The data indicate that the application of PHB can provide a beneficial effect to sea bass larviculture in terms of higher survival rates. But further studies are required to verify the impact on the developing immune system of the larvae

Biparental immune priming in the pipefish Syngnathus typhle

Highlights: • In a sex-role reversed pipefish, fathers have a major impact on offspring immunity. • Maternal effects are effective early in life but cease upon maturation. • Fathers provide long-term protection that comes with immunological specificity. • Long-term protection could be based on parental epigenetic traces. • Biparental immunological transfer comes with additive costs but lacks additive advantages. Abstract: The transfer of immunity from parents to offspring (trans-generational immune priming (TGIP)) boosts offspring immune defence and parasite resistance. TGIP is usually a maternal trait. However, if fathers have a physical connection to their offspring, and if offspring are born in the paternal parasitic environment, evolution of paternal TGIP can become adaptive. In Syngnathus typhle, a sex-role reversed pipefish with male pregnancy, both parents invest into offspring immune defence. To connect TGIP with parental investment, we need to know how parents share the task of TGIP, whether TGIP is asymmetrically distributed between the parents, and how the maternal and paternal effects interact in case of biparental TGIP. We experimentally investigated the strength and differences but also the costs of maternal and paternal contribution, and their interactive biparental influence on offspring immune defence throughout offspring maturation. To disentangle maternal and paternal influences, two different bacteria were used in a fully reciprocal design for parental and offspring exposure. In offspring, we measured gene expression of 29 immune genes, 15 genes associated with epigenetic regulation, immune cell activity and life-history traits. We identified asymmetric maternal and paternal immune priming with a dominating, long-lasting paternal effect. We could not detect an additive adaptive biparental TGIP impact. However, biparental TGIP harbours additive costs as shown in delayed sexual maturity. Epigenetic regulation may play a role both in maternal and paternal TGIP

Genomic variation among closely related Vibrio alginolyticus strains is located on mobile genetic elements

Background: Species of the genus Vibrio, one of the most diverse bacteria genera, have undergone niche adaptation followed by clonal expansion. Niche adaptation and ultimately the formation of ecotypes and speciation in this genus has been suggested to be mainly driven by horizontal gene transfer (HGT) through mobile genetic elements (MGEs). Our knowledge about the diversity and distribution of Vibrio MGEs is heavily biased towards human pathogens and our understanding of the distribution of core genomic signatures and accessory genes encoded on MGEs within specific Vibrio clades is still incomplete. We used nine different strains of the marine bacterium Vibrio alginolyticus isolated from pipefish in the Kiel-Fjord to perform a multiscale-comparative genomic approach that allowed us to investigate [1] those genomic signatures that characterize a habitat-specific ecotype and [2] the source of genomic variation within this ecotype. Results: We found that the nine isolates from the Kiel-Fjord have a closed-pangenome and did not differ based on core-genomic signatures. Unique genomic regions and a unique repertoire of MGEs within the Kiel-Fjord isolates suggest that the acquisition of gene-blocks by HGT played an important role in the evolution of this ecotype. Additionally, we found that ~ 90% of the genomic variation among the nine isolates is encoded on MGEs, which supports ongoing theory that accessory genes are predominately located on MGEs and shared by HGT. Lastly, we could show that these nine isolates share a unique virulence and resistance profile which clearly separates them from all other investigated V. alginolyticus strains and suggests that these are habitat-specific genes, required for a successful colonization of the pipefish, the niche of this ecotype. Conclusion We conclude that all nine V. alginolyticus strains from the Kiel-Fjord belong to a unique ecotype, which we named the Kiel-alginolyticus ecotype. The low sequence variation of the core-genome in combination with the presence of MGE encoded relevant traits, as well as the presence of a suitable niche (here the pipefish), suggest, that this ecotype might have evolved from a clonal expansion following HGT driven niche-adaptation