Disentangling relationships between physiology, morphology, diet, and gut microbial diversity in American Kestrel nestlings

Gut microbiota are increasingly recognized as important drivers of host health and fitness across vertebrate taxa. Given that gut microbial composition is directly influenced by the environment, gut microbiota may also serve as an eco-physiological mechanism connecting host ecology, such as diet, and physiology. Although gut microbiota have been well-studied in mammalian systems, little is known about how gut microbial diversity and composition impact morphological and physiological development in wild birds. Here, we characterized both diet and gut microbial diversity of free-living American kestrel (Falco sparverius) nestlings throughout development to test whether gut microbial diversity predicts host morphological and physiological traits in either contemporary or time-lagged manners. Gut microbial alpha diversity on day 21 of nestling development was positively correlated with diet alpha diversity representative of the majority of nestling development (days 5–20). Gut microbial alpha diversity early in development was negatively correlated with body mass in both contemporary and time-lagged manners. Gut microbial alpha diversity early in development was positively correlated with blood glucose later in development. As nestlings experience rapid growth demands in preparation to fledge, these time-lagged associations may indicate that gut microbial diversity at early critical developmental windows may determine the future trajectory of morphological and physiological traits underlying metabolism that ultimately impact fitness.

肠道菌群（gut microbiota）在各类脊椎动物类群中，正愈发被认可为调控宿主健康与适合度的关键因素。鉴于肠道菌群组成直接受环境影响，肠道菌群或可作为连接宿主生态学（如饮食）与生理学的生态生理学机制。尽管肠道菌群在哺乳动物体系中已得到充分研究，但针对野生鸟类中肠道菌群多样性与组成如何影响其形态与生理发育的认知仍较为匮乏。本研究对自由栖息的美洲红隼（Falco sparverius）雏鸟整个发育周期的饮食与肠道菌群α多样性（alpha diversity）进行了表征，以检验肠道菌群α多样性是否能以即时或时滞方式预测宿主的形态与生理性状。雏鸟发育第21天的肠道菌群α多样性，与代表雏鸟大部分发育阶段（第5至20天）的饮食α多样性呈正相关。发育早期的肠道菌群α多样性，在即时与时滞两种模式下均与体重呈负相关。发育早期的肠道菌群α多样性，与发育后期的血糖水平呈正相关。鉴于雏鸟在为出巢做准备时需满足快速生长的需求，这些时滞关联或表明：早期关键发育窗口内的肠道菌群多样性，或许决定了宿主代谢相关形态与生理性状的后续发展轨迹，而这些性状最终会影响宿主适合度。