The arborescent bryozoan Amathia verticillata (Delle Chiaje, 1822) can be found in both tropical and temperate waters but little is known on how natural dispersal and human-mediated transport mediates its current widespread distribution. The species can rapidly cover and dominate large areas of natural and artificial substrates, and infests port areas, ships, pipelines, and industrial marine installations. In addition, A. verticillata could be a complex of cryptic species, similar to many other bryozoan species with presumed cosmopolitan distributions. In this study, we tested whether A. verticillata represents a complex of cryptic species or it is a single species, and assessed whether natural and/or anthropogenic dispersal can explain its cosmopolitan distribution. We performed phylogenetic and population genetic analyses based on two mitochondrial genes (16S and COI) from samples collected in the United States, Brazil, Spain, Australia, and Mexico. Our results show a low genetic structure between Atlantic and Pacific oceans, with one haplotype of both genes widely distributed, while the other haplotypes (all with very low nucleotides diversity) were specific to each region. This suggests that A. verticillata is a single species, whose broad distribution seems to have been mediated by humans; the biology of the species in addition to its common occurrence near port areas also indicate this fact. However, to elucidate its origin and dispersal routes, a more extensive sampling effort and the usage of the genome-wide molecular markers should be explored. Until these studies are carried out, we recommend that the species should still be considered as cryptogenic.

在热带和温带水域均可发现乔木苔藓苔藓虫Amathia verticillata（Delle Chiaje，1822），但鲜为人知的是自然扩散和人类介导的运输如何介导其目前的广泛分布。该物种可以迅速覆盖并控制大面积的天然和人工底物，并侵染港口地区，船舶，管道和工业海洋设施。另外，与许多假定的世界性分布的其他苔藓虫物种相似，黄曲霉可能是隐性物种的复合体。在这项研究中，我们测试了A. verticillata代表复杂的隐物种或单一物种，并评估自然和/或人为传播是否可以解释其世界性分布。我们基于来自美国，巴西，西班牙，澳大利亚和墨西哥的两个线粒体基因（16S和COI）进行了系统发育和种群遗传分析。我们的结果表明，大西洋和太平洋之间的遗传结构较低，两种基因的一个单倍型广泛分布，而其他单倍型（均具有非常低的核苷酸多样性）是每个区域特有的。这表明，A。verticillata是单一物种，其广泛分布似乎是由人类介导的；该物种的生物学特性除了在港口附近地区普遍发生外，也表明了这一事实。但是，为阐明其起源和传播途径，应探索更广泛的采样方法和全基因组分子标记的使用。在进行这些研究之前，我们建议仍应将该物种视为隐源物种。