The first multi-gene phylogeny of the Macrostomorpha sheds light on the evolution of sexual and asexual reproduction in basal Platyhelminthes

The Macrostomorpha—an early branching and species-rich clade of free-living flatworms—is attracting interest because it contains Macrostomum lignano, a versatile model organism increasingly used in evolutionary, developmental, and molecular biology. We elucidate the macrostomorphan molecular phylogeny inferred from both nuclear (18S and 28S rDNA) and mitochondrial (16S rDNA and COI) marker genes from 40 representatives. Although our phylogeny does not recover the Macrostomorpha as a statistically supported monophyletic grouping, it (i) confirms many taxa previously proposed based on morphological evidence, (ii) permits the first placement of many families and genera, and (iii) reveals a number of unexpected placements. Specifically, Myozona and Bradynectes are outside the three classic families (Macrostomidae, Microstomidae and Dolichomacrostomidae) and the asexually fissioning Myomacrostomum belongs to a new subfamily, the Myozonariinae nov. subfam. (Dolichomacrostomidae), rather than ...

巨口目（Macrostomorpha）——一类早期分化且物种丰富的自由生活扁形虫支系（clade）——正受到关注，因其包含Macrostomum lignano这一多功能模式生物，该生物在进化生物学、发育生物学和分子生物学中的应用日益广泛。我们基于40个代表物种的核基因（18S和28S核糖体DNA，rDNA）及线粒体基因（16S核糖体DNA和细胞色素c氧化酶亚基I，COI）标记基因，阐明了巨口目的分子系统发育关系。尽管我们的系统发育树未将巨口目恢复为具有统计学支持的单系类群（monophyletic grouping），但它（i）证实了此前基于形态学证据提出的多个分类单元（taxa）；（ii）首次明确了多个科和属的系统位置；（iii）揭示了若干意外的分类地位。具体而言，Myozona和Bradynectes属位于三个经典科（巨口科Macrostomidae、微口科Microstomidae和长巨口科Dolichomacrostomidae）之外；而进行无性分裂的Myomacrostomum属属于一个新亚科——Myozonariinae nov. subfam.（隶属于长巨口科），而非...