Eukaryotic organisms vary widely in genome size and much of this variation can be explained by differences in the abundance of repetitive elements. However, the phylogenetic distributions and turnover rates of repetitive elements are largely unknown, particularly for species with large genomes. We therefore used de novo repeat identification based on low coverage whole-genome sequencing to characterize the repeatomes of six species of gomphocerine grasshoppers, an insect clade characterised by unusually large and variable genome sizes. Genome sizes of the six species ranged from 8.4 to 14.0 pg DNA per haploid genome and thus include the second largest insect genome documented so far (with the largest being another acridid grasshopper). Estimated repeat content ranged from 79 to 96% and was strongly correlated with genome size. Averaged over species, these grasshopper repeatomes comprised significant amounts of DNA transposons (24%), LINE elements (21%), helitrons (13%), LTR retrotransposons (12%) and satellite DNA (8.5%). The contribution of satellite DNA was particularly variable (ranging from <1% to 33%) as was the contribution of helitrons (ranging from 7 to 20%). The age distribution of divergence within clusters was unimodal with peaks around 4–6%. The phylogenetic distribution of repetitive elements was suggestive of an expansion of satellite DNA in the lineages leading to the two species with the largest genomes. Although speculative at this stage, we suggest that the expansion of satellite DNA could be secondary and might possibly have been favoured by selection as a means of stabilising greatly expanded genomes.

中文翻译：

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对 Gomphocerine Grashopper 基因组重复内容的比较分析揭示了基因组异常大的物种中卫星 DNA 和 Helitron 的扩展。


真核生物的基因组大小差异很大，这种差异大部分可以通过重复元件丰度的差异来解释。然而，重复元件的系统发育分布和周转率在很大程度上是未知的，特别是对于具有大基因组的物种。因此，我们使用基于低覆盖度全基因组测序的从头重复鉴定来表征六种 gomphocerine 蚱蜢的重复组，这是一种以异常大且可变的基因组大小为特征的昆虫进化枝。这六个物种的基因组大小范围为每个单倍体基因组 8.4 至 14.0 pg DNA，因此包括迄今为止记录的第二大昆虫基因组（最大的是另一种辛蚱蜢）。估计重复含量范围为 79% 至 96%，并且与基因组大小密切相关。按物种平均计算，这些蚱蜢重复组包含大量 DNA 转座子 (24%)、LINE 元件 (21%)、螺旋子 (13%)、LTR 反转录转座子 (12%) 和卫星 DNA (8.5%)。卫星 DNA 的贡献尤其多变（范围从 <1% 到 33%），日电子的贡献也是如此（范围从 7% 到 20%）。簇内分歧的年龄分布是单峰的，峰值在 4-6% 左右。重复元件的系统发育分布表明卫星DNA在谱系中的扩展导致了两个拥有最大基因组的物种。尽管现阶段还处于推测阶段，但我们认为卫星 DNA 的扩展可能是次要的，并且可能受到选择的青睐，作为稳定大幅扩展的基因组的一种手段。