Immunity for nothing and the eggs for free: Apparent lack of both physiological trade-offs and terminal reproductive investment in female crickets (Gryllus texensis)

Characterization of trade-offs between immunity and reproduction in the coral species Astrangia poculata

Background

Living organisms face ubiquitous pathogenic threats and have consequently evolved immune systems to protect against potential invaders. However, many components of the immune system are physiologically costly to maintain and engage, often drawing resources away from other organismal processes such as growth and reproduction. Evidence from a diversity of systems has demonstrated that organisms use complex resource allocation mechanisms to manage competing needs and optimize fitness. However, understanding of resource allocation patterns is limited across taxa. Cnidarians, which include ecologically important organisms like hard corals, have been historically understudied in the context of resource allocations. Improving understanding of resource allocation-associated trade-offs in cnidarians is critical for understanding future ecological dynamics in the face of rapid environmental change.

Methods

Here, we characterize trade-offs between constitutive immunity and reproduction in the facultatively symbiotic coral Astrangia poculata. Male colonies underwent ex situ spawning and sperm density was quantified. We then examined the effects of variable symbiont density and energetic budget on physiological traits, including immune activity and reproductive investment. Furthermore, we tested for potential trade-offs between immune activity and reproductive investment.

Results

We found limited associations between energetic budget and immune metrics; melanin production was significantly positively associated with carbohydrate concentration. However, we failed to document any associations between immunity and reproductive output which would be indicative of trade-offs, possibly due to experimental limitations. Our results provide a preliminary framework for future studies investigating immune trade-offs in cnidarians.

No life-history cost of tebufenozide resistance in the smaller tea tortrix moth

BACKGROUND

Tebufenozide is widely used to control populations of the smaller tea tortrix, Adoxophyes honmai. However, A. honmai has evolved resistance such that straightforward pesticide application is an untenable long-term approach for population control. Evaluating the fitness cost of resistance is key to devising a management strategy that slows the evolution of resistance.

RESULTS

We used three approaches to assess the life-history cost of tebufenozide resistance with two strains of A. honmai: a tebufenozide-resistant strain recently collected from the field in Japan and a susceptible strain that has been maintained in the laboratory for decades. First, we found that the resistant strain with standing genetic variation did not decline in resistance in the absence of insecticide over four generations. Second, we found that genetic lines that spanned a range of resistance profiles did not show a negative correlation between their LD₅₀ , the dosage at which 50 % of individuals died, and life-history traits that are correlates of fitness. Third, we found that the resistant strain did not manifest life-history costs under food limitation. Our crossing experiments indicate that the allele at an ecdysone receptor locus known to confer resistance explained much of the variance in resistance profiles across genetic lines.

CONCLUSION

Our results indicate that the point mutation in the ecdysone receptor, which is widespread in tea plantations in Japan, does not carry a fitness cost in the tested laboratory conditions. The absence of a cost of resistance and the mode of inheritance have implications for which strategies may be effective in future resistance management efforts. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Age, but not an immune challenge, triggers terminal investment in the Pacific field cricket, Teleogryllus oceanicus

The terminal investment hypothesis proposes that, when individuals are faced with a threat to survival, they will increase investment in current reproduction. The level of the threat necessary to elicit terminal investment (the dynamic terminal investment threshold) may vary based on other factors that also influence future reproduction. Here, we tested whether there is an interactive effect of age and an immune challenge on the dynamic terminal investment threshold in the Pacific field cricket, Teleogryllus oceanicus. We measured the courtship call, mating attractiveness, ejaculate size, and offspring production of T. oceanicus males. We found only limited support for the dynamic terminal investment threshold: there was no consistent evidence of a positive interaction between male age and immune challenge intensity. However, we found evidence for age-related terminal investment: older males produced a larger spermatophore than younger males. Older males also had a slower calling rate compared to younger males, suggesting a potential trade-off between these two pre- and post-copulatory traits. As some, but not all, reproductive traits responded plastically to cues for terminal investment, our research highlights the importance of considering a broad range of pre-and post-copulatory traits when exploring the potential for terminal investment to occur.

Induction of Multiple Immune Signaling Pathways in Gryllodes sigillatus Crickets during Overt Viral Infections

Despite decades of focus on crickets (family: Gryllidae) as a popular commodity and model organism, we still know very little about their immune responses to microbial pathogens. Previous studies have measured downstream immune effects (e.g., encapsulation response, circulating hemocytes) following an immune challenge in crickets, but almost none have identified and quantified the expression of immune genes during an active pathogenic infection. Furthermore, the prevalence of covert (i.e., asymptomatic) infections within insect populations is becoming increasingly apparent, yet we do not fully understand the mechanisms that maintain low viral loads. In the present study, we measured the expression of several genes across multiple immune pathways in Gryllodes sigillatus crickets with an overt or covert infection of cricket iridovirus (CrIV). Crickets with overt infections had higher relative expression of key pathway component genes across the Toll, Imd, Jak/STAT, and RNAi pathways. These results suggests that crickets can tolerate low viral infections but can mount a robust immune response during an overt CrIV infection. Moreover, this study provides insight into the immune strategy of crickets following viral infection and will aid future studies looking to quantify immune investment and improve resistance to pathogens.

Suppression of yolk formation, oviposition and egg quality of locust (Locusta migratoria manilensis) infected by Paranosema locustae

Locusta migratoria manilensis is one of the most important agricultural pests in China. The locust has high fecundity and consumes large quantities of food, causing severe damage to diverse crops such as corn, sorghum, and rice. Immunity against pathogens and reproductive success are two important components of individual fitness, and many insects have a trade-off between reproduction and immunity when resources are limited, which may be an important target for pest control. In this study, adult females L. migratoria manilensis were treated with different concentrations (5 × 106 spores/mL or 2 × 107 spores/mL) of the entomopathogenic fungus Paranosema locustae. Effects of input to immunity on reproduction were studied by measuring feeding amount, enzyme activity, vitellogenin (Vg) and vitellogenin receptor (VgR) production, ovary development, and oviposition amount. When infected by P. locustae, feeding rate and phenol oxidase and lysozyme activities increased, mRNA expression of Vg and VgR genes decreased, and yolk deposition was blocked. Weight of ovaries decreased, with significant decreases in egg, length and weight.Thus, locusts used nutritive input required for reproduction to resist invasion by microsporidia. This leads to a decrease in expression of Vg and VgR genes inhibited ovarian development, and greatly decreased total fecundity. P. locustae at 2 × 107 spores/mL had a more obvious inhibitory effect on the ovarian development in migratory locusts. This study provides a detailed trade-off between reproduction and immune input of the female, which provides a reliable basis to find pest targets for biological control from those trade-off processes.

Peanut triacylglycerols activate innate immunity both in insects and mammals

In this study, we investigated immunoreactivity of peanut (Arachis hypogaea) oil using the silkworm (Bombyx mori) model. The peanut oil induced melanin formation when injected to the silkworm hemocoel. We then purified the active substance and identified the triacylglycerols (TAGs) as the responsible molecule for the melanin-forming effect of peanut oil. Also, the peanut TAGs induced the muscle contraction of the silkworm (i.e., cleavage of the insect cytokine BmPP) and the TNF-α production by cultured mouse macrophage cells. The muscle contraction activity of the peanut TAGs was reduced by saponification reaction, indicating that the TAG (not the degraded fatty acids) moiety is responsible for the activity. The muscle contraction effects of other TAGs of olive, lard, and beef oil were comparable with that of peanut TAGs. Nevertheless, for the melanin formation, the effect of peanut TAGs was outstanding. The fatty acid composition of peanut TAGs was distinct from that of olive TAGs. These results suggest that TAGs are immunoreactive and induces cytokines both in insect and mammalian immune systems. Also, the differential effects of peanut and olive TAGs for the melanin formation may suggest that TAGs with different fatty acid compositions are distinguished by the immune system.

The developmental high wire: Balancing resource investment in immunity and reproduction

The strategic allocation of resources into immunity poses a unique challenge for individuals, where infection at different stages of development may result in unique trade-offs with concurrent physiological processes or future fitness-enhancing traits. Here, we experimentally induced an immune challenge in female Gryllus firmus crickets to test whether illness at discrete life stages differentially impacts fitness. We injected heat-killed Serratia marcescens bacteria into antepenultimate juveniles, penultimate juveniles, sexually immature adults, and sexually mature adults, and then measured body growth, instar duration, mating rate, viability of stored sperm, egg production, oviposition rate, and egg viability. Immune activation significantly impacted reproductive traits, where females that were immune challenged as adults had decreased mating success and decreased egg viability compared to healthy individuals or females that were immune challenged as juveniles. Although there was no effect of an immune challenge on the other traits measured, the stress of handling resulted in reduced mass gain and smaller adult body size in females from the juvenile treatments, and females in the adult treatments suffered from reduced viability of sperm stored within their spermatheca. In summary, we found that an immune challenge does have negative impacts on reproduction, but also that even minor acute stressors can have significant impacts on fitness-enhancing traits. These findings highlight that the factors affecting fitness can be complex and at times unpredictable, and that the consequences of illness are specific to when during an individual's life an immune challenge is induced.

Chronic immune challenge is detrimental to female survival, feeding behavior, and reproduction in the field cricket Gryllus assimilis (Fabricius, 1775)

Physiological trade-offs among expensive fitness-related traits, such as reproduction and immunity, are common in life histories of animals. An immune challenge can have different effects on female reproduction mediated by resource allocation and acquisition. In this study, employing a widely used method to challenge the insect immune system (nylon implant), we assessed the effects of mounting a chronic immune response simulating three successive immune assaults on survival and reproduction of mated females of Gryllus assimilis. We also verified feeding behavior following an implantation, which can be important in explaining trade-off dynamics in terms of energy acquisition. For this, three experimental groups were designed (Control, Sham, and Implant) with oviposition rates, egg morphometry, and nymph vigour observed over 3 weeks, at which ovarian mass and unlaid eggs were quantified from remaining individuals. The results showed that chronic implants were detrimental to female survival and reproduction throughout the experiments; Surgical Sham had no effect on survival compared to the control, but did on reproductive aspects such as oviposition rates and hatchling vigour. These negative effects on reproduction in Sham disappeared in the last experimental week, but still strong in the implanted females. Such immune challenge affected the feeding behavior of implanted females by reducing food consumption compared to control after infection, which is probably explained by illness-induced anorexia that takes place to maximize the immune system performance as a part of sickness behavior, exacerbating the adverse effects observed on reproduction (i.e., fewer and smaller eggs, and low vigour of nymphs) and survival.

Immunosenescence along with direct physiological allocation trade-offs between life history and immunity in the red palm weevil Rhynchophorus ferrugineus

Recent works have generally indicated that insects exhibit two immune response strategies: external and internal immune defense. However, the immune-related trade-offs and physiological regulatory mechanisms in red palm weevil, a major invasive pest, remain unclear. Based on postinfection survivorship experiments, we initially measured baseline constitutive external immunity (antibacterial activity of external secretions) and internal immunity (phenoloxidase and antibacterial activity of hemolymph) in uninfected individuals. Then, we challenged the individual immune system and examined subsequent investment in immune function. Our data showed that multiple factors (instar, age, sex, mating status, immune treatment) interacted to affect immune components and infection outcomes, but the magnitude and nature of the impact varied in each case. Although immune senescence is a common phenomenon in which immune function decreases with age, different components of the immune system changed differentially. Notably, mating activity may impose an immunity-related cost, with some evidence of sexual dimorphism and age-associated differences. Finally, parameters related to life-history traits usually decreased temporarily because of increased immunity, suggesting that the ultimate consequences of immune function fitness may be physiologically traded off with other fitness aspects, including growth, development, mating, reproduction, and longevity. These results reveal the complex factors that impact immunity as well as the physiological regulation of individual immunity, which may determine the evolution and outcome of immune senescence and trade-offs.

Sexual conflict drives micro- and macroevolution of sexual dimorphism in immunity

BACKGROUND

Sexual dimorphism in immunity is believed to reflect sex differences in reproductive strategies and trade-offs between competing life history demands. Sexual selection can have major effects on mating rates and sex-specific costs of mating and may thereby influence sex differences in immunity as well as associated host-pathogen dynamics. Yet, experimental evidence linking the mating system to evolved sexual dimorphism in immunity are scarce and the direct effects of mating rate on immunity are not well established. Here, we use transcriptomic analyses, experimental evolution and phylogenetic comparative methods to study the association between the mating system and sexual dimorphism in immunity in seed beetles, where mating causes internal injuries in females.

RESULTS

We demonstrate that female phenoloxidase (PO) activity, involved in wound healing and defence against parasitic infections, is elevated relative to males. This difference is accompanied by concomitant sex differences in the expression of genes in the prophenoloxidase activating cascade. We document substantial phenotypic plasticity in female PO activity in response to mating and show that experimental evolution under enforced monogamy (resulting in low remating rates and reduced sexual conflict relative to natural polygamy) rapidly decreases female (but not male) PO activity. Moreover, monogamous females had evolved increased tolerance to bacterial infection unrelated to mating, implying that female responses to costly mating may trade off with other aspects of immune defence, an hypothesis which broadly accords with the documented sex differences in gene expression. Finally, female (but not male) PO activity shows correlated evolution with the perceived harmfulness of male genitalia across 12 species of seed beetles, suggesting that sexual conflict has a significant influence on sexual dimorphisms in immunity in this group of insects.

CONCLUSIONS

Our study provides insights into the links between sexual conflict and sexual dimorphism in immunity and suggests that selection pressures moulded by mating interactions can lead to a sex-specific mosaic of immune responses with important implications for host-pathogen dynamics in sexually reproducing organisms.

Using silkworms to search for lactic acid bacteria that contribute to infection prevention and improvement of hyperglycemia

Bombyx mori, the silkworm, has biological functions in common with mammals, including humans. Since the molecular design of silkworm's innate immune system is analogous to that of mammals, understanding the silkworm's innate immunity is expected to contribute to the control of infection in humans. It is also possible to use silkworms to explore foodstuffs that activate innate immunity. Lactic acid bacteria have long been used in the production of fermented foods, and in recent years, their use as supplements has been attracting attention. Using silkworms, which are laboratory animals, functional lactic acid bacteria can be explored and isolated at low cost. Fermented foods produced by this method are expected to contribute to the maintenance of human health. In addition to the immune system, humans and silkworms share a common mechanism for maintaining blood glucose homeostasis, and it is possible to construct a pathological model of diabetes and search for therapeutic substances using silkworms. Taken together, we propose that the silkworm is useful for assessing the functions of lactic acid bacterial for health purposes.

High-Stakes Decision-Making by Female Crickets (Gryllus texensis): When to Trade In Wing Muscles for Eggs

AbstractResource-intensive traits, such as dispersal and reproduction, can be difficult to express simultaneously because of resource limitations. One solution is to switch between resource-intensive behaviors. Such phenotypic plasticity is one strategy that organisms use to funnel resources from one expensive trait to another. In crickets (Gryllus texensis), the development and maintenance of flight muscles reduce resource availability for reproduction, leading to physiological trade-offs between the two traits. Long-winged female G. texensis can histolyze their wing muscles, resulting in increased egg production, but they can then no longer fly. Using a diet that mimics food availability in the field, we found that long-winged females adopted one of the three following strategies: early reproduction, intermediate reproduction, and late reproduction. Some late reproducers maintained their flight capability until the end of their natural life span and laid few eggs. If females lost the ability to fly (i.e., their hind wings are removed), they laid eggs earlier, leading to increased reproductive output. However, other environmental cues (e.g., an increased number of mates, increased oviposition substrate quality, or a bout of dispersal flight) had no effect. Late-reproducing females laid 96% fewer eggs than early reproducers, suggesting that late reproduction exacts a huge fitness cost. Nevertheless, some females maintain their flight muscles to the end of their natural life span in both the lab and the field. We suggest that the ability to fly allows for bet hedging against an environmental catastrophe (e.g., drought or flood). This benefit may help explain the persistence of late-reproducing long-winged females, despite the cost of this choice. As climate change increases drought and flood in Texas, late dispersal may be one factor that helps this species survive in the future. An increased understanding of factors that maintain seemingly low fitness strategies can help us predict the resilience of species under climate change.

IRP30 promotes worker egg-laying in bumblebee, Bombus terrestris (Hymenoptera: Apidae)

Bumblebees are important pollinators that have evolved between solitary and advanced eusocial insects. Compared with advanced honeybees, workers of social bumblebee species are prone to laying eggs during the competition phase, which leads to the end of the colony. Therefore, worker reproductive behavior has become a popular research topic for exploring various biological phenomena. Here, we demonstrate a novel reproduction-related function of an immune response protein-encoding gene (Immune Responsive Protein 30, IRP30) in Bombus terrestris by employing RNA interference (RNAi) and a transgenic Drosophila melanogaster system. The results show that worker egg-laying was significantly affected by IRP30 expression levels (P < 0.01). Compared with those in the dsGFP-treated groups, the first egg-laying time was delayed by 3.7 d and the egg number was decreased by 41% in the dsIRP30-treated group. In addition, the average size of the largest oocyte and the relative mRNA expression levels of Vg (vitellogenin) were significantly reduced in the dsIRP30-treated group (P < 0.05). Cellular localization by immunofluorescence demonstrated that IRP30 has important functions in the germ cells of workers' ovarioles. Overexpression of IRP30 was confirmed to increase the reproductive capability of the transgenic D. melanogaster. In conclusion, IRP30 regulates worker egg-laying by affecting the expression of Vg, the size of the ovary and the formation of the oocyte. These findings provide essential information for understanding the mechanisms underlying worker reproductive regulation.

Innate immune system function following systemic RNA-interference of the Fragile X Mental Retardation 1 gene in the cricket Acheta domesticus

Fragile X syndrome (FXS), caused by a mutation in the Fragile X Mental Retardation 1 (FMR1) gene, is a common form of inherited mental retardation. Mutation of the gene leads to a loss of the gene product Fragile X Mental Retardation Protein (FMRP). While a loss of FMRP has been primarily associated with neural and cognitive deficits, it has also been reported to lead to immune system dysfunction in both humans and flies. We used the Acheta domesticus transcriptome to identify a highly conserved cricket ortholog of FMR1 (adfmr1). We cloned a partial cDNA of adfmr1, used systemic RNA interference (RNAi) to knockdown adfmr1 expression, and examined the impact of this knockdown (KD) on the cellular and humoral responses of the insect innate immune system. Following RNAi, both male and female crickets exhibited an increase in the number of circulating hemocytes, a decrease in total hemolymph phenoloxidase (PO) activity, and an increase in fat body lysozyme expression. Despite similar changes in these immune parameters in both sexes, male and female crickets responded differently to an immune challenge. Most KD males failed to survive an intra-abdominal injection of bacterial lipopolysaccharide, while KD females were just as likely as control females to survive this challenge. Our results support that decreased fmr1 expression can alter the cellular and humoral defenses of the insect innate immune system, and may lead to a decrease in male, but not female, immunocompetence.

C-Type Lectins Link Immunological and Reproductive Processes in Aedes aegypti

Physiological trade-offs between mosquito immune response and reproductive capability can arise due to insufficient resource availability. C-type lectin family members may be involved in these processes. We established a GCTL-3-/- mutant Aedes aegypti using CRISPR/Cas9 to investigate the role of GCTL-3 in balancing the costs associated with immune responses to arboviral infection and reproduction. GCTL-3-/- mutants showed significantly reduced DENV-2 infection rate and gut commensal microbiota populations, as well as upregulated JAK/STAT, IMD, Toll, and AMPs immunological pathways. Mutants also had significantly shorter lifespans than controls and laid fewer eggs due to defective germ line development. dsRNA knock-down of Attacin and Gambicin, two targets of the AMPs pathway, partially rescued this reduction in reproductive capabilities. Upregulation of immune response following GCTL-3 knock-out therefore comes at a cost to reproductive fitness. Knock-out of other lectins may further improve our knowledge of the molecular and genetic mechanisms underlying reproduction-immunity trade-offs in mosquitoes.