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 (Mirounga angustirostris ) during a critical developmental window of 6 weeks after weaning, when the pups stay ashore without feeding. We found substantial sex differences in the early‐life gut microbiome, even though males and females could not yet be distinguished morphologically. Sex and age both explained around 15% of the variation in gut microbial beta diversity, while microbial communities sampled from the same individual showed high levels of similarity across time, explaining another 40% of the variation. Only a small proportion of the variation in beta diversity was explained by health status, assessed by full blood counts, but clinically healthy individuals had a greater microbial alpha diversity than their clinically abnormal peers. Across the post‐weaning period, the northern elephant seal gut microbiome was highly dynamic. We found evidence for several colonization and extinction events as well as a decline in Bacteroides 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 was correlated with gut microbiome similarity in males but not females, again reflecting 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.

中文翻译：

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北部象海豹发育中的肠道微生物组中的早期性二态性。

肠道微生物组是物种生态系统不可或缺的一部分，但我们对寄主特性如何影响其在野生种群中的发育知之甚少。在这里，我们探索了这些内在因素在塑造北象海豹（Mirounga angustirostris）的肠道微生物组中的作用。），在断奶后6周的关键发育期中，幼崽不进食就停留在岸上。我们发现早期肠道微生物组存在巨大的性别差异，即使尚不能从形态上区分出男性和女性。性别和年龄都解释了肠道微生物β多样性变化的15％左右，而从同一个人采样的微生物群落随时间变化显示出高度相似性，解释了另外40％的变化。β多样性的变异中只有一小部分是通过全血细胞计数评估的健康状况来解释的，但是临床健康的个体比其临床异常的同伴具有更大的微生物α多样性。在断奶后的整个过程中，北象海豹肠道微生物组非常活跃。拟杆菌属和普雷沃氏菌的增加，这种模式以前与从护理到固体食品的转变有关。最后，我们证明了遗传相关性与男性而非女性的肠道微生物组相似性相关，再次反映了早期的性别差异。我们的研究代表了自然饮食控制和纵向调查，该调查研究了内在因素如何塑造一个形态和生活史具有极端性别差异的物种的早期肠道微生物组。