Transposable elements (TEs) are a major determinant of eukaryotic genome size. The collective properties of a genomic TE community reveal the history of TE/host evolutionary dynamics and impact present-day host structure and function, from genome to organism levels. In rare cases, TE community/genome size has greatly expanded in animals, associated with increased cell size and changes to anatomy and physiology. Here, we characterize the TE landscape of the genome and transcriptome in an amphibian with a giant genome — the caecilian Ichthyophis bannanicus, which we show has a genome size of 12.2 Gb. Amphibians are an important model system because the clade includes independent cases of genomic gigantism. The I. bannanicus genome differs compositionally from other giant amphibian genomes, but shares a low rate of ectopic recombination-mediated deletion. We examine TE activity using expression and divergence plots; TEs account for 15% of somatic transcription, and most superfamilies appear active. We quantify TE diversity in the caecilian, as well as other vertebrates with a range of genome sizes, using diversity indices commonly applied in community ecology. We synthesize previous models that integrate TE abundance, diversity, and activity, and test whether the caecilian meets model predictions for genomes with high TE abundance. We propose thorough, consistent characterization of TEs to strengthen future comparative analyses. Such analyses will ultimately be required to reveal whether the divergent TE assemblages found across convergent gigantic genomes reflect fundamental shared features of TE/host genome evolutionary dynamics.

转座因子 (TE) 是真核生物基因组大小的主要决定因素。基因组 TE 社区的集体特性揭示了 TE/宿主进化动力学的历史，并影响了当今宿主结构和功能，从基因组到生物体水平。在极少数情况下，动物的 TE 群落/基因组大小已大大扩大，这与细胞大小的增加以及解剖学和生理学的变化有关。在这里，我们描述了一种具有巨大基因组的两栖动物的基因组和转录组的 TE 景观——我们展示了其基因组大小为 12.2 Gb的caecilian Ichthyophis bannanicus。两栖动物是一个重要的模型系统，因为该进化枝包括基因组巨人症的独立案例。在一bannanicus基因组在组成上与其他巨型两栖动物基因组不同，但异位重组介导的缺失率较低。我们使用表达图和散度图检查 TE 活动；TEs 占体细胞转录的 15%，大多数超家族似乎都很活跃。我们使用群落生态学中常用的多样性指数，量化了caecilian 以及其他具有一系列基因组大小的脊椎动物的TE 多样性。我们综合了之前整合了 TE 丰度、多样性和活性的模型，并测试了 caecilian 是否满足高 TE 丰度基因组的模型预测。我们建议对 TE 进行彻底、一致的表征，以加强未来的比较分析。