Stott Caroline, Diop Awa, Raymann Kasie, Bobay Louis-Marie
Department of Biological Sciences, North Carolina State University, Raleigh, NC 27695, USA.
Department of Biology, University of North Carolina Greensboro, Greensboro, NC 27412, USA.
Mol Biol Evol. 2024 Dec 6;41(12). doi: 10.1093/molbev/msae256.
Microbial communities that maintain symbiotic relationships with animals evolve by adapting to the specific environmental niche provided by their host, yet understanding their patterns of speciation remains challenging. Whether bacterial speciation occurs primarily through allopatric or sympatric processes remains an open question. In addition, patterns of DNA transfers, which are pervasive in bacteria, are more constrained in a closed host-gut system. Eusocial bees have co-evolved with their specialized microbiota for over 85 million years, constituting a simple and valuable system to study the complex dynamics of host-associated microbial interactions. Here, we studied the patterns of speciation and evolution of seven specialized gut bacteria from three clades of eusocial bee species: western honey bees, eastern honey bees, and bumblebees. We conducted genomic analyses to infer species delineation relative to the patterns of homologous recombination (HR), and horizontal gene transfer (HGT). The studied bacteria presented various modes of evolution and speciation relative to their hosts, but some trends were consistent across all of them. We observed a clear interruption of HR between bacteria inhabiting different bee hosts, which is consistent with a mechanism of allopatric speciation, but we also identified interruptions of HR within hosts, suggesting recent or ongoing sympatric speciation. In contrast to HR, we observed that HGT events were not constrained by species borders. Overall, our findings show that in host-associated bacterial populations, patterns of HR and HGT have different impacts on speciation patterns, which are driven by both allopatric and sympatric speciation processes.
与动物保持共生关系的微生物群落通过适应宿主提供的特定环境生态位而进化，但了解它们的物种形成模式仍然具有挑战性。细菌物种形成主要是通过异域或同域过程发生的，这仍然是一个悬而未决的问题。此外，在细菌中普遍存在的DNA转移模式，在封闭的宿主肠道系统中受到更多限制。群居蜜蜂与其特化的微生物群共同进化了超过8500万年，构成了一个研究宿主相关微生物相互作用复杂动态的简单而有价值的系统。在这里，我们研究了来自群居蜜蜂三个分支的七种特化肠道细菌的物种形成和进化模式：西方蜜蜂、东方蜜蜂和熊蜂。我们进行了基因组分析，以推断相对于同源重组（HR）和水平基因转移（HGT）模式的物种划分。所研究的细菌相对于其宿主呈现出各种进化和物种形成模式，但其中一些趋势在所有细菌中都是一致的。我们观察到栖息在不同蜜蜂宿主中的细菌之间的HR明显中断，这与异域物种形成机制一致，但我们也发现宿主内部的HR中断，表明近期或正在进行的同域物种形成。与HR不同，我们观察到HGT事件不受物种边界的限制。总体而言，我们 的研究结果表明，在宿主相关细菌种群中，HR和HGT模式对物种形成模式有不同影响，这是由异域和同域物种形成过程共同驱动的。
