Tradeoffs between mounting an immune response and territorial singing behavior in mountain white-crowned sparrows

Abstract

Sexually selected traits are often plastic and can thus provide information on infection status and parasite load. Mounting an immune response has been shown to require the diversion of energy and resources away from other life history functions. Previous studies have demonstrated that bird song may be influenced by an immune challenge. We investigated how mounting an immune response by mountain white-crowned sparrows Zonotrichia leucophrys oriantha affects specific aspects of territorial song and behavior. We used song playback to simulate a territorial intrusion and elicit baseline song and behavioral defense responses. Individuals were then either injected with a lipopolysaccharide (LPS) solution to induce an acute immune response, or a saline control. Post-treatment territorial song and behaviors in response to playback were recorded 1 day and 7 days later. The immune challenge significantly reduced the number of birds that sang compared to control individuals on Day 1. Alarm behaviors increased, and the few birds that did sing on Day 1 sang abnormal songs at significantly slower rates and with fewer terminal notes. By Day 7, the number of LPS-treated males that sang equaled the number of singing control birds, and song structure and rates returned to baseline levels. However, on Day 7, LPS-treated birds had elevated rates of alarm behaviors. Responses were variable and, with the exception of whether birds sang or not, comparisons that simply compared individuals within a time period across treatment and control were not as sensitive as those that compared the difference between baseline and post-treatment responses across treatment groups. This suggests that for the most sensitive assessment of immune status, prior experience of an individual’s behavior is necessary. This study also reveals that simply mounting an immune response to infection, as opposed to the actual infection per se is sufficient to impact avian song production. 3

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