Data from: House sparrows offset the physiological trade-off between immune response and feather growth by adjusting foraging behavior

Growing feathers and mounting immune responses are both energetically costly for birds. According to the life history trade-off hypothesis, it has been posited that the costs of feather growth lead to temporal isolation between molt and other expensive activities, reproduction for example. In contrast to life cycle events, the need to mount an immune response can occur at any time, including during feather growth. Thus, we hypothesized that mounting an immune response during feather growth may divert energy and resources from feather growth and impair feather renewal. To test this hypothesis, we clipped or plucked the same feathers of male house sparrows, Passer domesticus biblicus. In the clipped group (n = 16), the feathers were absent with no regrowth; in the plucked group (n = 14), feathers were absent and regrowth was initiated. We also had an intact control group of 15 sparrows. We then initiated an inflammatory immune response by subcutaneous injection over the left breast muscle of the birds with a lipopolysaccharide (LPS) and quantified behavioral and physiological responses. We predicted that sparrows with plucked feathers would incur the highest energetic costs while mounting an immune response, and would increase their foraging effort to offset this cost. We found no difference in body mass and resting metabolic rates among sparrows subjected to the different feather and immune treatments. However, we did find that while sparrows with plucked feathers increased foraging efficiency following the immune challenge by paying fewer but longer visits to the food tray, allowing them to maintain food consumption. Foraging efficiency in sparrows with clipped feathers was reduced. We also found that quality of newly grown feathers after the immune challenge was poorer in the plucked group, suggesting that mounting an immune response competes with feather growth for resources.

对于鸟类而言，羽毛生长与启动免疫应答均属于高能耗生理过程。根据生活史权衡假说（life history trade-off hypothesis），已有研究推测，羽毛生长的能量成本会导致换羽与其他高能耗活动（如繁殖）在时间上出现隔离。与生命周期固有事件不同，免疫应答的启动时机不受限制，甚至可能发生在羽毛生长阶段。据此，我们提出假设：在羽毛生长期间启动免疫应答，会将原本用于羽毛生长的能量与资源转移，进而损害羽毛更新进程。为验证该假设，我们对雄性家麻雀（Passer domesticus biblicus）的同一部位羽毛分别实施修剪或拔取处理：修剪组（n=16）的羽毛被剪除且未出现再生；拔取组（n=14）的羽毛被拔除并启动了再生过程；另设置15只完整羽毛的家麻雀作为对照组。随后，我们通过在鸟类左侧胸肌皮下注射脂多糖（lipopolysaccharide, LPS）诱导炎症性免疫应答，并量化其行为与生理响应。我们预测，拔取羽毛的家麻雀在启动免疫应答时将承受最高的能量成本，因此会通过提升觅食努力来抵消该额外消耗。研究结果显示，接受不同羽毛处理与免疫处理的家麻雀，其体重与静息代谢率未出现显著差异。但我们观察到，拔取羽毛的家麻雀在受到免疫挑战后，通过减少觅食频次但延长单次在食槽前的停留时长来提升觅食效率，从而维持了食物摄入量；而修剪羽毛组的家麻雀觅食效率则出现下降。此外，免疫挑战后新生长羽毛的质量在拔取组中更差，这表明启动免疫应答会与羽毛生长竞争有限的资源。