Abstract
Ecoimmunology is the study of the causes and consequences of variation in immunity. This integrative field builds on and complements comparative immunology by evaluating immunity across levels of biological organization using an evolutionary and ecological framework. One major accomplishment of ecoimmunology has been to demonstrate that immune defenses have costs, and these costs can be context-dependent. As a result, researchers assess immunity not only in terms of specific immune pathways but also as functional, emergent traits, such as resistance against and tolerance of parasites. Ecoimmunology also highlights the importance of integration across physiological systems, including the immune, endocrine, and nervous systems, in the production of immune defenses. The field has demonstrated the importance of genetics, developmental environment, and current conditions to individual variation in immune function and emphasized the traits of species, such as body size, that could be integral to immune phenotypes. Furthermore, ecoimmunological studies have shown that heterogeneity in immunity at the individual and species levels can have important consequences for disease dynamics within populations and communities as well as population cycling. Herein we discuss these key research areas in ecoimmunology as they relate to three central themes: (1) immunity in the context of the whole organism, (2) heterogeneity in immunity, and (3) the broad consequences of individual variation in immunity. We conclude by reviewing future directions for ecoimmunology, focusing on those that could have important implications for public health, conservation, and wildlife management.