Costs of immune responses are related to host body size and lifespan.

Amber J Brace,Jennifer L Grindstaff,Dana M Hawley,Katherine L Buchanan,Lynn B Martin,Kevin D Matson,Marc J Lajeunesse,Jeanne M Fair,Daniel R Ardia,James S Adelman

doi:10.1002/jez.2084

Abstract

A central assumption in ecological immunology is that immune responses are costly, with costs manifesting directly (e.g., increases in metabolic rate and increased amino acid usage) or as tradeoffs with other life processes (e.g., reduced growth and reproductive success). Across taxa, host longevity, timing of maturity, and reproductive effort affect the organization of immune systems. It is reasonable, therefore, to expect that these and related factors should also affect immune activation costs. Specifically, species that spread their breeding efforts over a long lifetime should experience lower immune costs than those that mature and breed quickly and die comparatively early. Likewise, body mass should affect immune costs, as body size affects the extent to which hosts are exposed to parasites as well as how hosts can combat infections (via its effects on metabolic rates and other factors). Here, we used phylogenetic meta-regression to reveal that, in general, animals incur costs of immune activation, but small species that are relatively long-lived incur the largest costs. These patterns probably arise because of the relative need for defense when infection risk is comparatively high and fitness can only be realized over a comparatively long period. However, given the diversity of species considered here and the overall modest effects of body mass and life history on immune costs, much more research is necessary before generalizations are appropriate.

Highlights

Protection against infection often comes at a cost to hosts (Lochmiller and Deerenberg, 2000)
We focused exclusively on functional costs of immunity such as changes in body mass, physical performance, food intake, growth rate, egg production, egg size, gonad size, breeding effort, survival probability, recruitment success, and dispersal behavior when exposed to an immune system stimulant (Bonneaud et al, 2003a, Cox and Calsbeek, 2010, Klasing and Korver, 1997, Bonneaud et al, 2004, Laugero and Moberg, 2000)
Variation in these costs was substantially beyond that predicted by sampling error; there is little evidence for a file drawer problem for null results; the file drawer problem refers to the possibility that many null results might not have been published, often because of concerns about the lack of statistical power to be confident that effects are genuinely absent (Rosenberg, 2005)

Summary

Introduction

Protection against infection often comes at a cost to hosts (Lochmiller and Deerenberg, 2000). Longer-lived and slower-to-mature organisms likely experience overall greater exposure to parasites, and different trajectories of immune ontogeny, than fastdeveloping, prolifically-breeding species. Some support from this expectation comes from the recurrent observation that some long-lived species favor specific immune defenses over non-specific ones (Martin et al, 2007). The reasons for this pattern are thought to be twofold. But non-exclusively, by favoring specific defenses (with memory), long-lived organisms might avoid recurrent collateral damage (costs) associated with non-specific defenses (Ricklefs and Wikelski, 2002)

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Discussion

Conclusion