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）作为脊椎动物类群中宿主健康与生存适合度的关键驱动因子，正日益受到学界的广泛认可。鉴于肠道菌群组成直接受环境因素影响，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机制。尽管哺乳动物体系中的肠道菌群研究已较为充分，但目前对野生鸟类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相对匮乏。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多样性进行了系统表征，旨在验证肠道菌群多样性是否能以即时或滞后关联的方式预测宿主的形态与生理性状。研究结果显示：雏鸟发育至第21天时的肠道菌群α多样性（alpha diversity），与代表雏鸟多数发育阶段（第5至20天）的饮食α多样性呈显著正相关；发育早期的肠道菌群α多样性，无论以即时还是滞后关联模式，均与体质量呈显著负相关；同时，发育早期的肠道菌群α多样性与后续发育阶段的血糖水平呈显著正相关。由于雏鸟为准备离巢需经历快速生长阶段，上述滞后关联提示：早期关键发育窗口内的肠道菌群多样性，或可决定宿主代谢相关形态与生理性状的后续发展轨迹，最终影响其生存适合度。