Quantification of Thermal Acclimation in Immune Functions in Ectothermic Animals

This short review focuses on current experimental designs to quantify immune acclimation in animals. Especially in the face of rapidly changing thermal regimes, thermal acclimation of immune function has the potential to impact host-pathogen relationships and the fitness of hosts. While much of the field of ecoimmunology has focused on vertebrates and insects, broad interest in how animals can acclimate to temperatures spans taxa. The literature shows a recent increase in thermal acclimation studies in the past six years. I categorized studies as focusing on (1) natural thermal variation in the environment (e.g., seasonal), (2) in vivo manipulation of animals in captive conditions, and (3) in vitro assays using biological samples taken from wild or captive animals. I detail the strengths and weaknesses of these approaches, with an emphasis on mechanisms of acclimation at different levels of organization (organismal and cellular). These two mechanisms are not mutually exclusive, and a greater combination of the three techniques listed above will increase our knowledge of the diversity of mechanisms used by animals to acclimate to changing thermal regimes. Finally, I suggest that functional assays of immune system cells (such as quantification of phagocytosis) are an accessible and non-taxa-specific way to tease apart the effects of animals upregulating quantities of immune effectors (cells) and changes in the function of immune effectors (cellular performance) due to structural changes in cells such as those of membranes and enzymes.