Hildebrandt Julia C, Eisenbarth Albert, Renz Alfons, Streit Adrian
Department for Evolutionary Biology, Max Planck Institute for Developmental Biology, Spemannstrasse 35, D-72076 Tübingen, Germany.
Institute of Evolution and Ecology, Department of Comparative Zoology, University of Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany; Programme Onchocercoses field station of the University of Tübingen, BP 65 Ngaoundéré, Cameroon.
Vet Parasitol. 2014 Sep 15;205(1-2):318-29. doi: 10.1016/j.vetpar.2014.06.006. Epub 2014 Jun 14.
Onchocerca ochengi is a nodule-forming filarial nematode parasite of cattle in tropical Africa and closely related to the human pathogen Onchocerca volvulus. The adult worms reside in intradermal nodules. While females are sedentary, males may move between nodules. The first stage larvae (microfilariae) disperse in the skin of the host waiting to be taken up by the intermediate host. The density of microfilariae in the skin is largely independent of the number of adult worms present indicating some form of density dependent control. Recently, Onchocerca sp. Siisa, a form of Onchocerca distinguishable from O. ochengi by mitochondrial DNA sequences but not by morphology, was described to occur in cattle. This raised the question if Onchocerca sp. Siisa represents a different mitochondrial clade of O. ochengi or a new species. In order to study the reproductive biology and to understand this self-control of the off-spring population we systematically analyzed all Onchocerca nodules from the skin of one zebu cow and we examined a sample of microfilariae from a skin biopsy. We identified 87 O. ochengi females and 146 males. 56 (64.4%) of the females contained developing embryos. In order to assign the progeny to their respective parents we determined the genotypes at six nuclear and two mitochondrial molecular genetic markers in the adult worms, in a fraction of the progeny present in the uteri of the females and in the skin microfilariae. The 121 skin microfilariae we analyzed originated from at least 17 different mothers, which contributed rather differently to the total. Forty-five larvae (37.2%) were the progeny of a single female. Of the adult worms 16.7% were of the type Onchocerca sp. Siisa. These worms appeared to interbreed freely with the rest of the O. ochengi population and therefore belong to the same species.
奥氏盘尾丝虫是热带非洲牛的一种形成结节的丝虫线虫寄生虫，与人类病原体旋盘尾丝虫密切相关。成虫寄生于皮下结节中。雌性成虫固定不动，而雄性成虫可能在结节之间移动。第一期幼虫（微丝蚴）散布在宿主皮肤中，等待被中间宿主摄取。皮肤中微丝蚴的密度在很大程度上与成虫数量无关，这表明存在某种形式的密度依赖性控制。最近，有报道称盘尾丝虫属的西萨种（Onchocerca sp. Siisa）存在于牛体内，它通过线粒体DNA序列可与奥氏盘尾丝虫区分开来，但形态上无法区分。这就提出了一个问题，即盘尾丝虫属的西萨种是奥氏盘尾丝虫的一个不同线粒体分支还是一个新物种。为了研究其生殖生物学并了解后代种群的这种自我控制机制，我们系统地分析了一头瘤牛皮肤中的所有盘尾丝虫结节，并检查了皮肤活检样本中的微丝蚴。我们鉴定出87只奥氏盘尾丝虫雌性成虫和146只雄性成虫。56只（64.4%）雌性成虫体内含有发育中的胚胎。为了将后代与其各自的亲本进行匹配，我们在成虫、部分雌性成虫子宫内的后代以及皮肤微丝蚴中，测定了六个核分子遗传标记和两个线粒体分子遗传标记的基因型。我们分析的121只皮肤微丝蚴至少来自17个不同的母体，它们对总数的贡献差异较大。45只幼虫（37.2%）是单一雌性成虫的后代。在成虫中，16.7%属于盘尾丝虫属的西萨种类型。这些虫子似乎与其余的奥氏盘尾丝虫种群自由杂交，因此属于同一物种。
