Although numerous studies have found horizontal transposon transfer (HTT) to be widespread across metazoans, few have focused on HTT in marine ecosystems. To investigate potential recent HTTs into marine species, we searched for novel repetitive elements in sea snakes, a group of elapids which transitioned to a marine habitat at most 18 Ma. Our analysis uncovered repeated HTTs into sea snakes following their marine transition. The seven subfamilies of horizontally transferred LINE retrotransposons we identified in the olive sea snake (Aipysurus laevis) are transcribed, and hence are likely still active and expanding across the genome. A search of 600 metazoan genomes found all seven were absent from other amniotes, including terrestrial elapids, with the most similar LINEs present in fish and marine invertebrates. The one exception was a similar LINE found in sea kraits, a lineage of amphibious elapids which independently transitioned to a marine environment 25 Ma. Our finding of repeated horizontal transfer events into marine snakes greatly expands past findings that the marine environment promotes the transfer of transposons. Transposons are drivers of evolution as sources of genomic sequence and hence genomic novelty. We identified 13 candidate genes for HTT-induced adaptive change based on internal or neighboring HTT LINE insertions. One of these, ADCY4, is of particular interest as a part of the KEGG adaptation pathway “Circadian Entrainment.” This provides evidence of the ecological interactions between species influencing evolution of metazoans not only through specific selection pressures, but also by contributing novel genomic material.

中文翻译：

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新环境，新入侵者——线向海蛇的重复水平转移

尽管许多研究发现水平转座子转移 (HTT) 在后生动物中广泛存在，但很少有人关注海洋生态系统中的 HTT。为了调查最近 HTT 对海洋物种的潜在影响，我们在海蛇中寻找新的重复元素，海蛇是一群在 18 Ma 时过渡到海洋栖息地的海蛇。我们的分析发现，海蛇在海洋过渡后反复出现 HTT。我们在橄榄海蛇（Aipysurus laevis) 被转录，因此可能仍然活跃并在整个基因组中扩展。对 600 个后生动物基因组的搜索发现，其他羊膜动物（包括陆生 elapids）中都没有所有 7 个后生动物基因组，其中最相似的 LINEs 存在于鱼类和海洋无脊椎动物中。一个例外是在海环蛇中发现的类似 LINE，这是一种两栖 elapids 的谱系，可独立过渡到 25 Ma 的海洋环境。我们对海洋蛇重复水平转移事件的发现大大扩展了过去海洋环境促进转座子转移的发现。转座子是进化的驱动因素，作为基因组序列的来源，因此是基因组新颖性的来源。我们根据内部或相邻的 HTT LINE 插入确定了 13 个用于 HTT 诱导的适应性变化的候选基因。其中之一，ADCY4，作为 KEGG 适应途径“昼夜节律夹带”的一部分特别令人感兴趣。这提供了物种之间生态相互作用的证据，不仅通过特定的选择压力，而且还通过提供新的基因组材料来影响后生动物的进化。