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

Abstract

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 3weeks, 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. Thesenegative 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.