Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Sweden.
Department of Organismal Biology, Systematic Biology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
Genome Biol Evol. 2020 Mar 1;12(3):88-102. doi: 10.1093/gbe/evaa018.
Satellite DNA (satDNA) is an abundant class of tandemly repeated noncoding sequences, showing high rate of change in sequence, abundance, and physical location. However, the mechanisms promoting these changes are still controversial. The library model was put forward to explain the conservation of some satDNAs for long periods, predicting that related species share a common collection of satDNAs, which mostly experience quantitative changes. Here, we tested the library model by analyzing three satDNAs in ten species of Schistocerca grasshoppers. This group represents a valuable material because it diversified during the last 7.9 Myr across the American continent from the African desert locust (Schistocerca gregaria), and this thus illuminates the direction of evolutionary changes. By combining bioinformatic and cytogenetic, we tested whether these three satDNA families found in S. gregaria are also present in nine American species, and whether differential gains and/or losses have occurred in the lineages. We found that the three satDNAs are present in all species but display remarkable interspecies differences in their abundance and sequences while being highly consistent with genus phylogeny. The number of chromosomal loci where satDNA is present was also consistent with phylogeny for two satDNA families but not for the other. Our results suggest eminently chance events for satDNA evolution. Several evolutionary trends clearly imply either massive amplifications or contractions, thus closely fitting the library model prediction that changes are mostly quantitative. Finally, we found that satDNA amplifications or contractions may influence the evolution of monomer consensus sequences and by chance playing a major role in driftlike dynamics.
卫星 DNA（satDNA）是一类丰富的串联重复非编码序列，在序列、丰度和物理位置上表现出高变率。然而，促进这些变化的机制仍存在争议。库模型被提出来解释一些 satDNA 的长期保守性，预测相关物种共享一组共同的 satDNA，这些 satDNA 主要经历数量上的变化。在这里，我们通过分析十种草螽目蝗虫物种中的三个 satDNA 来检验库模型。这个群体是一个有价值的材料，因为它在过去的 7900 万年里从非洲沙漠蝗（Schistocerca gregaria）在美洲大陆多样化，这阐明了进化变化的方向。通过结合生物信息学和细胞遗传学，我们测试了这三个 satDNA 家族是否也存在于九种美洲物种中，以及在进化枝中是否发生了差异增益和/或损失。我们发现这三个 satDNA 存在于所有物种中，但在丰度和序列上存在显著的种间差异，同时与属系统发育高度一致。satDNA 存在的染色体位点数量也与两个 satDNA 家族的系统发育一致，但与另一个家族不一致。我们的结果表明，satDNA 的进化主要是偶然事件。几个进化趋势显然暗示着大规模的扩增或收缩，因此与库模型的预测非常吻合，即变化主要是数量上的。最后，我们发现 satDNA 的扩增或收缩可能会影响单体共识序列的进化，并通过机会在漂移动力学中发挥主要作用。
