Sex differences in immunity in a natural population of bush-cricket (Orthoptera: Phaneropterinae)

Abstract

Immune defense often differs between sexes, where females generally exhibit higher individual immunity than males. Such sexually dimorphic immune defense stems from differential investment into reproduction as females allocate more resources into mating. Contrary to prevailing predictions, some studies have found that females exhibit a weaker immune response than males. In this study, I examined both humoral (phenoloxidase activity and lytic activity) and cellular (encapsulation ability) immune parameters including cuticular melanization in a field population of a bush-cricket (Isophya reticulata) that is an endemic species in the northeastern part of Turkey. As expected, females showed a higher phenoloxidase activity than males, whereas there were no sex differences in lytic activity. Males expressed a higher encapsulation response than females. These results indicated that sex differences in immunity may be variable and females may not always exhibit higher immunity than males. Another interesting finding of this study was a positive relationship between stridulatory file length, phenoloxidase activity, and wing melanization. This finding demonstrated a connection between size differences in stridulatory apparatus that affect sexual signaling and immune response.