The brown alga Scytosiphon lomentaria (Scytosiphonaceae, Ectocarpales) has been reported from cold and warm waters worldwide. Although previous molecular phylogenetic studies and crossing experiments have shown that it is a complex of multiple distinct species, the taxonomic position and accurate distribution of each species have remained largely unclear. For the S. lomentaria complex from Japan, our cox1 and rbcL phylogenetic analyses detected six species. In addition to five previously detected species (species Ia–Va), one species (species VI) was newly found in the subtropical area, Okinawa Island. Species VI was recovered as a sister to species Ia–Va in rbcL. Based on the morphological and phylogenetic data, we concluded that species Ia is S. lomentaria, species IIIa is S. promiscuus, and the other four species are newly described: S. shibazakiorum for species IIa, S. tosaensis for species IVa, S. arcanus for species Va, and S. subtropicus for species VI. The cox1‐based analysis also showed that S. lomentaria, S. shibazakiorum, and S. promiscuus have worldwide distributions, while the other three species were not found outside of Japan. In Japan, except for S. subtropicus, distributions of these species overlapped. Our crossing experiments showed that gametic incompatibility (pre‐zygotic barrier) was less developed between the allopatric species (i.e., S. subtropicus and others) compared with the sympatric species. It may suggest that pre‐zygotic barriers have evolved among the sympatric species due to reinforcement.

中文翻译：

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来自日本的六种虹吸虫物种（虹吸藻科，藻科）的系统学，分布和性相容性，以及四种新物种的描述

在世界各地的冷水和温水中均已报道了棕色藻类Scytosiphon lomentaria（Scytosiphonaceae，Ectocarpales）。尽管以前的分子系统发育研究和杂交实验表明，它是由多个不同物种组成的复合体，但每个物种的分类位置和准确分布仍不清楚。对于来自日本的S. lomentaria复合体，我们的cox 1和rbc L系统发育分析检测到6种。除了先前发现的五个物种（物种Ia–Va）之外，在亚热带地区冲绳岛还新发现了一个物种（物种VI）。物种VI被回收为rbc中Ia–Va物种的姐妹L.根据形态学和系统发育数据，我们得出结论，物种Ia是S. lomentaria，物种IIIa是S. promiscuus，另外四个新描述的物种：S. shibazakiorum代表IIa物种，S. tosaensis代表IVa物种，S. arcanus物种Va和S. subtropicus物种VI。该COX -1开始的分析还表明S. lomentaria，S. shibazakiorum和S. promiscuus具有全球分布，而其他三个品种均未发现日本以外。在日本，除了亚热带链球菌，这些物种的分布重叠。我们的杂交实验表明，与同胞种相比，同种异体物种（即亚热带沙门氏菌和其他亚种）之间的配子不相容性（合子前屏障）较少发展。这可能表明，由于强化，共生物种之间已经形成了合子前障碍。