Data from: Microsatellite evolutionary rate and pattern in Schistocerca gregaria inferred from direct observation of germline mutations

Unravelling variation among taxonomic orders regarding the rate of evolution in microsatellites is crucial for evolutionary biology and population genetics research. The mean mutation rate of microsatellites tends to be lower in arthropods than in vertebrates, but data are scarce and mostly concern accumulation of mutations in model species. Based on parent-offspring segregations and a hierarchical Bayesian model, the mean rate of mutation in the orthopteran insect Schistocerca gregaria was estimated at 2.1e-4 per generation per untranscribed dinucleotide locus. This is close to vertebrate estimates and one order of magnitude higher than estimates from species of other arthropod orders, such as Drosophila melanogaster and Daphnia pulex. We also found evidence of a directional bias towards expansions even for long alleles and exceptionally large ranges of allele sizes. Finally, at transcribed microsatellites, the mean rate of mutation was half the rate found at untranscribed loci and the mutational model deviated from that usually considered, with most mutations involving multistep changes that avoid disrupting the reading frame. Our direct estimates of mutation rate were discussed in the light of peculiar biological and genomic features of S. gregaria, including specificities in mismatch repair and the dependence of its activity to allele length. Shedding new light on the mutational dynamics of grasshopper microsatellites is of critical importance for a number of research fields. As an illustration, we showed how our findings improve microsatellite application in population genetics, by obtaining a more precise estimation of S. gregaria effective population size from a published data set based on the same microsatellites.

阐明不同分类群阶元间微卫星（microsatellites）演化速率的差异，对演化生物学和群体遗传学研究至关重要。微卫星的平均突变率在节肢动物（arthropods）中往往低于脊椎动物，但相关数据较为匮乏，且大多聚焦于模式物种的突变积累情况。基于亲子代分离分析与分层贝叶斯（hierarchical Bayesian）模型，我们估算出直翅目昆虫沙漠蝗（Schistocerca gregaria）在非转录二核苷酸位点上的平均突变为每代每位点2.1×10^-4。这一数值与脊椎动物的估算结果相近，且比其他节肢动物阶元物种（如果蝇 Drosophila melanogaster、蚤状溞 Daphnia pulex）的估算结果高一个数量级。我们还发现，即便针对长等位基因以及等位基因长度范围极广的位点，也存在偏向扩增的突变方向性偏倚证据。最后，在转录区微卫星上，平均突变率仅为非转录区位点的一半，且其突变模型与常规认知存在偏差：绝大多数突变涉及多步改变，且不会破坏阅读框。我们结合沙漠蝗（S. gregaria）独特的生物学与基因组学特征，对直接估算的突变率展开了讨论，其中包括错配修复（mismatch repair）系统的特异性，以及其活性对等位基因长度的依赖性。阐明蝗虫微卫星的突变动态机制，对诸多研究领域均具有重要意义。举例而言，我们基于同一套微卫星标记的已发表数据集，通过更精准地估算沙漠蝗的有效种群规模（effective population size），展示了本研究结果如何优化微卫星在群体遗传学中的应用。