Early sexual dimorphism in the developing gut microbiome of northern elephant seals. Northern elephant seal gut microbiome

The gut microbiome is an integral part of a species’ ecology, but we know little about how host characteristics impact its development in wild populations. Here, we explored the role of such intrinsic factors in shaping the gut microbiome of northern elephant seals during a critical developmental window of six weeks after weaning, when the pups stay ashore without feeding. We show that the early-life gut microbiome is already substantially different in male and female pups, even though males and females cannot yet be distinguished morphologically. Sex and age both explain around 15% of the variation in gut microbial beta diversity, while microbial communities sampled from the same individual show high levels of similarity across time, explaining another 40% of the variation. Only a small proportion of the variation in beta diversity is explained by health status, but healthy individuals have a greater microbial alpha diversity than their non-healthy peers. Across the post-weaning period, the elephant seal gut microbiome is highly dynamic. We found evidence for several colonisation and extinction events as well as a decline in Bacteriodes and an increase in Prevotella, a pattern that has previously been associated with the transition from nursing to solid food. Lastly, we show that genetic relatedness is correlated with gut microbiome similarity in males but not females, again reflecting substantial early sex-differences. Our study represents a naturally diet-controlled and longitudinal investigation of how intrinsic factors shape the early gut microbiome in a species with extreme sex differences in morphology and life history.

肠道微生物组（gut microbiome）是物种生态学的核心组成部分，但我们对宿主特征如何影响野生种群中肠道微生物组的发育却知之甚少。本研究聚焦于断奶后六周这一关键发育窗口期，探讨此类内在因素对北象海豹肠道微生物组塑造的作用——此时幼崽会停留在海岸且无需进食。研究发现，即便雄性与雌性幼崽在形态上尚且无法区分，其早期肠道微生物组已存在显著差异。性别与年龄均可解释约15%的肠道微生物组β多样性变异，而同一宿主不同时间点采集的微生物群落具有高度相似性，这又解释了40%的变异来源。仅有小部分β多样性变异可由健康状况解释，但健康个体的微生物α多样性显著高于非健康个体。在断奶后的整个阶段，北象海豹的肠道微生物组具有高度动态性。本研究观测到多次菌群定植与消亡事件，同时发现拟杆菌属（Bacteroides）丰度下降、普雷沃菌属（Prevotella）丰度上升的模式——这一模式此前被认为与从哺乳到进食固体食物的转变相关。最后，研究发现雄性个体的遗传亲缘关系与肠道微生物组相似性呈正相关，而雌性个体则无此关联，这进一步体现了早期发育阶段显著的性别差异。本研究针对一种形态与生活史存在极端性别差异的物种，开展了天然饮食受控的纵向研究，揭示了内在因素如何塑造其早期肠道微生物组。