Dominance and immune function in the F1 generation of wild caught field crickets

Female Gryllus bimaculatus have been found to prefer dominant males as mates, and dominant males have shown to have a higher encapsulation rates and higher lytic activities. However, previous studies were conducted with crickets from the laboratory stock culture population that has been in the laboratory for years. Under laboratory conditions, low rates of natural parasites and pathogens may cause unexpected correlations with immune function and life history traits. As a continuation of our previous work, we tested whether the male fighting ability, predicting dominance status, is associated with immune function in the F1 offspring from field collected individuals. To define male dominance we arranged fights between males. Interestingly, the dominance was related to one measure of immune response, but not another. Similarly to previous studies, dominant males had higher encapsulation rates than their subordinates. However, in contrast to earlier studies, dominant males had lower lysozyme-enzyme activities than subordinate males. Furthermore, encapsulation rates and lytic activities correlated negatively with each other. Lytic activities correlated positively with male body mass and encapsulation rates correlated negatively with the male’s body mass. Thus, the current results do not support the hypothesis that dominant males would always have better overall immunocompetence, but rather, suggests that varying environmental conditions may reflect the importance of the immune defence with respect to the success in male-male contests.