Document Type

Article

Publication Date

2008

Publication Title

The American Naturalist

Volume

172

Issue

3

First Page

E99

Last Page

E112

DOI

10.1086/589521

Abstract

Organisms theoretically manage their immune systems optimally across their life spans to maximize fitness. However, we lack information on (1) how the immune system is managed across life‐history stages, (2) whether the sexes manage immunity differentially, and (3) whether immunity is repeatable within an individual. We present a within‐individual, repeated‐measures experiment examining life‐history stage variation in the inflammatory immune response in the zebra finch (Taeniopygia guttata). In juveniles, age‐dependent variation in immune response differed in a sex‐ and context‐specific manner, resulting in no repeatability across stages. In adults, females displayed little stage‐dependent variation in immune response when laying while receiving a high‐quality (HQ) diet; however, laying while receiving a low‐quality (LQ) diet significantly reduced both immune responses and reproductive outputs in a manner consistent with a facultative (resource‐driven) effect of reproduction on immunity. Moreover, a reduced immune response in females who were raising offspring while receiving an HQ diet suggests a residual effect of the energetic costs of reproduction. Conversely, adult males displayed no variation in immune responses across stages, with high repeatability from the nonbreeding stage to the egg‐laying stage, regardless of diet quality (HQ diet, $r=0.51$; LQ diet, $r=0.42$). Females displayed high repeatability when laying while receiving the HQ diet ($r=0.53$); however, repeatability disappeared when individuals received the LQ diet. High‐response females receiving the HQ diet had greater immune flexibility than did low‐response females who were laying while receiving the LQ diet. Data are consistent with immunity being a highly plastic trait that is sex‐specifically modulated in a context‐dependent manner and suggest that immunity at one stage may provide limited information about immunity at future stages.

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