Herlyn Holger, Piskurek Oliver, Schmitz Jürgen, Ehlers Ulrich, Zischler Hans
Primate Genetics, German Primate Center, Kellnerweg 4, Göttingen 37077, Germany.
Mol Phylogenet Evol. 2003 Jan;26(1):155-64. doi: 10.1016/s1055-7903(02)00309-3.
The phylogeny of the Syndermata (Rotifera: Monogononta, Bdelloidea, Seisonidea; Acanthocephala: Palaeacanthocephala, Eoacanthocephala, Archiacanthocephala) is key to understanding the evolution of acanthocephalan endoparasitism from free-living ancestors. In the present study, maximum likelihood, distance/neighbor-joining, and maximum parsimony analyses have been carried out based on 18S rDNA data of 22 species (four new sequences). The results suggest a monophyletic origin of the Eurotatoria (Monogononta+Bdelloidea). Seison appears as the acanthocephalan sistergroup. Palaeacanthocephala split into an "Echinorhynchus"-and a "Leptorhynchoides"-group, the latter sharing a monophyletic origin with the Eoacanthocephala and Archiacanthocephala. As inferred from the phylogeny obtained acanthocephalan endoparasitism evolved from a common ancestor of Seison and Acanthocephala that lived epizoically on an early mandibulate. Probably, an acanthocephalan stem species invaded the mandibulate host, thus establishing an endoparasitic lifestyle. Subsequently, vertebrates (or gnathostomes) became part of the parasite's life cycle. In the stem line of the Archiacanthocephala, a terrestrial life cycle has evolved, with an ancestor of the Tracheata (Insecta, Myriapoda) acting as intermediate host.
Syndermata（轮虫纲：单巢目、蛭态目、海轮虫目；棘头动物门：古棘头虫纲、新棘头虫纲、始新棘头虫纲）的系统发育对于理解棘头虫从自由生活祖先演化而来的内寄生现象至关重要。在本研究中，基于22个物种（4个新序列）的18S rDNA数据进行了最大似然法、距离/邻接法和最大简约法分析。结果表明欧洲轮虫类（单巢目+蛭态目）起源于单系群。海轮虫目是棘头动物的姐妹群。古棘头虫纲分为一个“棘吻虫属”组和一个“细颈棘头虫属”组，后者与新棘头虫纲和始新棘头虫纲起源于单系群。从所获得的系统发育推断，棘头虫的内寄生现象是从海轮虫目和棘头动物的一个共同祖先演化而来，该祖先在早期有颚类动物体表营外寄生生活。可能是一个棘头虫的祖先物种侵入了有颚类宿主，从而建立了内寄生生活方式。随后，脊椎动物（或有颌类）成为了寄生虫生命周期中的一部分。在始新棘头虫纲的主干谱系中，演化出了一个陆地生命周期，气管类（昆虫纲、多足纲）的一个祖先作为中间宿主。
