Adaptive radiations offer an excellent opportunity to understand the eco-evolutionary dynamics of gut microbiota and host niche specialization. In a laboratory common garden, we compared the gut microbiota of two novel trophic specialists, a scale-eater and a molluscivore, to a set of four outgroup generalist populations from which this adaptive radiation originated. We predicted an adaptive and highly divergent microbiome composition in the specialists matching their rapid rates of craniofacial diversification in the past 10 kya. We measured gut lengths and sequenced 16S rRNA amplicons of gut microbiomes from lab-reared fish fed the same high protein diet for one month. In contrast to our predictions, gut microbiota largely reflected 5 Mya phylogenetic divergence times among generalist populations in support of phylosymbiosis. However, we did find significant enrichment of Burkholderiaceae bacteria in both lab-reared scale-eater populations. These bacteria sometimes digest collagen, the major component of fish scales, supporting an adaptive shift. We also found some enrichment of Rhodobacteraceae and Planctomycetacia in lab-reared molluscivore populations, but these bacteria target cellulose. Minor shifts in gut microbiota appear adaptive for scale-eating in this radiation, whereas overall microbiome composition was phylogenetically conserved. This contrasts with predictions of adaptive radiation theory and observations of rapid diversification in all other trophic traits in these hosts, including craniofacial morphology, foraging behavior, aggression, and gene expression, suggesting that microbiome divergence proceeds as a nonadaptive radiation.

中文翻译：

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食蟹小对虾适应性辐射中肠道微生物组的非适应性辐射，有微小的变化以进食鳞片

适应性辐射为了解肠道菌群的生态进化动力学和宿主生态位专门化提供了极好的机会。在实验室的公共花园中，我们将两名新的营养专家，食鳞动物和软体动物的肠道菌群与这种适应性辐射起源的一组四个外来通才种群进行了比较。我们预测专家的适应性和高度差异性微生物组组成与其过去10 kya中颅面多样化的快速速度相匹配。我们测量了肠道的长度，并对来自饲喂相同高蛋白饮食一个月的实验室饲养鱼的肠道微生物群的16S rRNA扩增子进行了测序。与我们的预测相反，肠道菌群主要反映了通才群体中5种Mya系统发生差异，以支持共生。然而，我们确实在两个实验室饲养的食鳞动物种群中都发现了Burkholderiaceae细菌的大量富集。这些细菌有时会消化胶原蛋白（鱼鳞的主要成分），从而支持适应性转变。我们还发现，在实验室饲养的软体动物种群中，红细菌科和浮游菌有一些富集，但这些细菌以纤维素为目标。肠道微生物区系的微小变化似乎适合在这种辐射下食鳞，而总体微生物组组成在系统发育上是保守的。这与适应性辐射理论的预测以及这些寄主的所有其他营养性状（包括颅面形态，觅食行为，侵略性和基因表达）快速多样化的观察结果相反，表明微生物组的发散是作为非适应性辐射而进行的。