Mating enhances parasite resistance in the cricket Gryllus texensis

Reproduction and immunity are both costly functions, and therefore, there may be selection pressures for animals to trade-off one against the other to maximize reproductive success. We tested whether female crickets, Gryllus texensis, when manipulated to invest more energy in reproduction, showed a reduced ability to combat infection by (1) analysing mortality following injections of Serratia marcescens (host resistance test); and (2) measuring total phenoloxidase (PO) activity of the haemolymph. Although mated females had greater reproductive costs relative to virgins, we found no evidence that they had decreased immune capacity as measured by host resistance or PO activity of the haemolymph. In fact, based on the host resistance test, mated females were more resistant to infection than were virgins. Disease resistance is enhanced as early as 2 days following mating and lasts for several days. Mated females manipulated to lay different numbers of eggs did not differ in their disease resistance. These results are consistent with the following hypotheses: (1) mated cricket females receive compounds that enhance female disease resistance (i.e. direct benefits) from males; (2) mating cues females to up-regulate immune responsiveness, possibly due to an increased risk of disease transmission; (3) mating cues females to alter the distribution of their immune resources, thereby increasing resistance to some pathogens, but possibly decreasing resistance to others.