Meeting Abstract
Immune function is often involved in physiological trade-offs because of the energetic costs of maintaining the immune system and mounting responses to pathogens. However, immune function is not a single trait, but rather a collection of discrete immune factors. Given limited resources, animals should allocate towards factors that combat the parasite threat with the highest fitness cost. In addition, physiological stress may differentially affect distinct immune factors and allocation priority rules to competing life history demands. In this study, we tested how function of distinct immune factors varies between dispersal phenotypes of a dimorphic cricket and how physiological stress influences allocation to these immunity factors. We measured lysozyme activity, which defends against bacteria and encapsulation, which can destroy parasite eggs. We also stressed the crickets with a sham predator in a full factorial design. Patterns of investment in immune factors could be explained by the major parasite threat likely to be encountered by each morph and was affected by physiological stress. The results suggest that maintaining rapid, constitutive defenses may drive trade-offs between lysozyme activity and encapsulation. Furthermore, the selective pressures exerted by parasites may help maintain dimorphism in some insects via disruptive selection.
