Mounting an immune response to infection is energetically expensive and forces a dilemma between investing in survival or reproduction. The environmental and life history characteristics of the host and parasite, including gender, age, resource availability, and virulence, influence the relative benefits of somatic maintenance and terminal investment for organismal fitness. While studies on a variety of taxa have described infection-induced terminal investment, it remains unclear to what extent the change in reproduction can respond plastically to the strength of infection cues like initial dose or virulence. Furthermore, parental adoption of these strategies could influence the quality and quantity of offspring, including the strength of primed immunity provided across generations. To investigate the impact of infection strength on the plasticity of the terminal investment response and its relationship with trans-generational immune priming, we exposed female adult flour beetles (Tribolium castaneum) to different doses of heat-killed Bacillus thuringiensis (Bt), including doses that successfully induced trans-generational priming in previous studies. We counted eggs as a measure of fecundity and measured hatching rate to estimate offspring quality. We then quantified offspring survival against a lethal dose of Bt to estimate the impact of maternal infection-induced reproductive strategy on the strength of trans-generational immune priming.
Results/Conclusions
Our results suggest that maternal fecundity rates respond plastically to dose. Mothers exposed to intermediate doses of bacteria reduce their egg laying rate but also produce primed offspring, suggesting that somatic maintenance improves the quality of both maternal and offspring defenses. Our study suggests that counterintuitive results in reproductive investment studies can be accounted for by understanding the relationship between maternal and offspring immune investment. These results should also spur the investigation of natural variation in infection-induced reproductive plasticity among insect taxa that show variation in their ability to prime offspring against infection.