许多寄生虫及其宿主的形态相似性导致人们猜测,动物,真菌,藻类寄生虫可能直接从它们的宿主进化而来。这些寄生虫,在植物学文献中被称为adelphoparasites,最近,昆虫文献中的寄生物,可能从一个宿主单生进化,然后辐射到其他宿主,这些寄生虫可能是多系统发育的,每个人都来自自己的主机。在这项研究中,我们比较了红色藻类寄生虫属Asterocolax及其宿主中包含的物种和特殊形态(宿主种族)的核核糖体重复序列的内部转录间隔区,它们都属于Delesseriaceae的Phycodrys群,并且与Delesseriaceae的非宿主类群密切相关。这些分析表明,Asterocolax的物种已经进行了多系统发育。来自北大西洋寄主的赤丝红斑似乎是从其寄主进化而来的,而包含在北太平洋物种中的类群有两个独立的起源。来自宿主背阔神经多神经的Asterocolaxgardneri可能直接来自该宿主。相比之下,所有其他特殊形式的GardneriA.gardneria似乎都起源于Phycodryssetchellii或Isabelliae,并二次辐射到Phycodrys组的其他密切相关的类群上,包括Nienburgiaandersoniana和Anisocladellapacifica。配子杂交实验证实,来自每个宿主的A.gardneri是从其两个宿主中遗传分离的,还有其他A.Gardneri和他们的主人。交叉感染实验表明,A.gardneri仅在其天然宿主上正常发育,尽管在备用宿主上可能会发生一些异常生长。红藻寄生虫二次辐射到其他红藻类群的能力,在那里它们可能会被基因分离和物种化,这表明,这种物种形成过程不是一个“遗传死胡同”,而是一个可能导致相关的寄生虫物种集群的过程。
Morphological similarities of many parasites and their hosts have led to speculation that some groups of plant, animal, fungal, and algal parasites may have evolved directly from their hosts. These parasites, which have been termed adelphoparasites in the botanical literature, and more recently, agastoparasites in the insect literature, may evolve monophyletically from one host and radiate secondarily to other hosts or, these parasites may arise polyphyletically, each arising from its own host. In this study we compare the internal transcribed spacer regions of the nuclear ribosomal repeats of species and formae specialis (host races) included in the red algal parasite genus Asterocolax with its hosts, which all belong to the Phycodrys group of the Delesseriaceae and with closely related nonhost taxa of the Delesseriaceae. These analyses reveal that species of Asterocolax have evolved polyphyletically. Asterocolax erythroglossi from the North Atlantic host Erythroglossum laciniatum appears to have evolved from its host, whereas taxa included in the north Pacific species Asterocolax gardneri have had two independent origins. Asterocolax gardneri from the host Polyneura latissima probably arose directly from this host. In contrast, all other A. gardneri formae specialis appear to have originated from either Phycodrys setchellii or P. isabelliae and radiated secondarily onto other closely related taxa of the Phycodrys group, including Nienburgia andersoniana and Anisocladella pacifica. Gamete crossing experiments confirm that A. gardneri from each host is genetically isolated from both its host, and from other A. gardneri and their hosts. Cross-infection experiments reveal that A. gardneri develops normally only on its natural host, although some abberrant growth may occur on alternate hosts. The ability of red algal parasites to radiate secondarily to other red algal taxa, where they may become isolated genetically and speciate, suggests that this process of speciation is not a \"genetic dead end\" but one that may give rise to related clusters of parasite species.