Department of Biology, Lund University, Ecology Building, 223 62 Lund, Sweden.
Proc Biol Sci. 2023 Aug 30;290(2005):20230794. doi: 10.1098/rspb.2023.0794. Epub 2023 Aug 16.
Non-lethal infections are common in free-living animals and the associated sickness behaviours can impact crucial life-history trade-offs. However, little is known about the duration and extent of such sickness behaviours in free-living animals, and consequently how they affect life-history decisions. Here, free-living Eurasian blackbirds, , were immune-challenged with lipopolysaccharide (LPS) to mimic a bacterial infection and their behaviour was monitored for up to 48 days using accelerometers. As expected, immune-challenged birds were less active than controls within the first 24 h. Unexpectedly, this reduced activity remained detectable for 20 days, before both groups returned to similar activity levels. Furthermore, activity was positively correlated with a pre-experimental index of complement activity, but only in immune-challenged birds, suggesting that sickness behaviours are modulated by constitutive immune function. Differences in daily activity levels stemmed from immune-challenged birds resting earlier at dusk than control birds, while activity levels between groups were similar during core daytime hours. Overall, activity was reduced by 19% in immune-challenged birds and they were on average almost 1 h less active per day for 20 days. This unexpected longevity in sickness behaviour may have severe implications during energy-intense annual-cycle stages (e.g. breeding, migration, winter). Thus, our data help to understand the consequences of non-lethal infections on free-living animals.
非致死性感染在自由生活的动物中很常见，相关的患病行为会影响关键的生活史权衡。然而，对于自由生活的动物中这种患病行为的持续时间和程度，以及它们如何影响生活史决策，我们知之甚少。在这里，我们用脂多糖（LPS）对自由生活的欧亚鸲进行免疫挑战，以模拟细菌感染，并使用加速度计监测它们的行为长达 48 天。正如预期的那样，免疫挑战后的鸟类在最初的 24 小时内比对照组的活动量要少。出乎意料的是，这种减少的活动量在 20 天后仍可检测到，之后两组恢复到相似的活动水平。此外，活动量与实验前补体活性指数呈正相关，但仅在免疫挑战组的鸟类中，这表明患病行为受固有免疫功能的调节。每日活动水平的差异源于免疫挑战组的鸟类在黄昏时比对照组的鸟类更早地休息，而在核心白天时间，两组的活动水平相似。总的来说，免疫挑战组的鸟类活动量减少了 19%，并且在 20 天内每天的活动量平均减少了近 1 小时。这种患病行为的意外持久可能会对能量密集的年度周期阶段（如繁殖、迁徙、冬季）产生严重影响。因此，我们的数据有助于理解非致死性感染对自由生活动物的后果。
