Summary1. Reproduction and immune function are critical processes, but organisms can rarely optimize both traits. Resultant reproduction-immunity trade-offs may be 'facultative', occurring only when resources are scarce, or they may be 'obligate', occurring regardless of resource availability.2. Previous research has tested for the 'facultative' or 'obligate' nature of reproduction-immunity trade-offs by measuring resource allocation (e.g. follicle size). However, measuring resource allocation alone may be insufficient when gauging the fitness consequences of reproduction-immunity trade-offs because the number and quality of eggs or offspring trade off with one another. 3. We used the Texas field cricket (Gryllus texensis) to provide the most direct test to date of whether a fitness trade-off between these two traits is 'facultative' or 'obligate'. We used a factorial design to manipulate food availability and immune status throughout adulthood. We then estimated lifetime fecundity, hatching success and their product (reproductive success), and we also measured several aspects of offspring quality (e.g. egg size and protein content, and hatchling size and energy stores). 4. A reproduction-immunity trade-off was 'obligate' in this species because immune challenge reduced reproductive success estimates regardless of food availability. Females with unlimited food were more fecund and produced more and larger hatchlings, but neither food availability nor immune status affected egg size, egg phenoloxidase activity, incubation duration, hatching success or hatchling energy stores. We observed a trade-off between offspring size and number -females favouring offspring size over fecundity produced fewer hatchlings, but their hatchlings were of higher quality (larger and more robust). 5. By demonstrating that not all eggs are created equal, we provide key insight into the role of reproductive allocation in the fitness trade-off between reproduction and immunity.
Summary Animal immune systems must adaptively balance aggressive immune resistance (ability to destroy pathogens) with infection tolerance (ability to withstand the negative effects of infection; e.g. immunopathology or damage due to pathogen metabolism). Insects offer unique insight into this balancing act because phenoloxidase (PO)‐mediated melanization is a key feature of immune resistance, but PO activation obligates the production of nonspecific reactive species that can cause self‐damage. The antioxidant glutathione (GSH) can provide protection against such reactive molecules, but high levels of GSH can impair melanization. In support of the hypothesis that GSH can protect insects (e.g. crickets) from self‐damage during an immune response, we found that bacterially infected crickets showed a significant positive relationship between GSH haemolymph concentration and fecundity after controlling for bacterial growth rate. That is, GSH may be a mechanism of infection tolerance because it correlated with fecundity despite bacterial proliferation. Next, we factorially manipulated food availability and immune activation in female crickets to examine whether the relative balance between a component of immune resistance (i.e. PO) and protection from self‐damage (i.e. GSH) was plastic and sensitive to environmental conditions. Glutathione and PO were positively correlated, and the PO:GSH ratio was robust and not affected by food availability or immune activation. Thus, increased investment in a mechanism of immune resistance may obligate a concomitant increase in GSH to reduce self‐damage (i.e. increase infection tolerance). Chronic immune activation led to greater tolerance of oxidative stress suggesting that repeated immune activation upregulates infection tolerance mechanisms. Food limitation led to reduced PO activity, but not GSH concentration. This result suggests that mechanisms of immune resistance may be more sensitive to resource scarcity than mechanisms of infection tolerance. We demonstrate that some mechanisms of immune resistance and infection tolerance can be correlated and that they can be affected by food availability or immune activation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.