Adult female crickets, Gryllus texensis, maintain reproductive output after repeated immune challenges

Both immunity and reproduction are thought to be energetically costly and therefore likely to make trade-offs with one another. To assess whether increasing immune system activity results in a decline in egg production, the immune system in the cricket Gryllus texensis is activated over a period of 12 days with regular injections of lipopolysaccharide (LPS) derived from Serratia marcescens, and the number of eggs laid during this time counted. Egg quality is also assessed by measuring total protein of eggs laid, fertilization and hatching success, and the weight of individual eggs laid after the series of injections. Indirect evidence suggests that LPS induces an immune response in G. texensis. However, the number of eggs produced is not affected. There is also no effect of repeated LPS injections on female weight, egg protein content, or fertilization and hatching success. Taken together, these results suggest that with food and water provided ad libitum, females can protect many aspects of fitness in the face of increased immune system activity. However, there is some evidence to suggest that large (100 mu g) doses of LPS lead to reduced female longevity, and also in egg weight that could affect offspring success. Although the possibility exists that the decline in lifespan and egg weight after high-dose injections reflects a trade-off between reproduction and immune investment, another possibility is that these doses yield nonspecific effects, or that the high-dose induces an overwhelming immune response that leads to self-damage.