Department of Aquatic Animal Medicine, College of Fisheries, Huazhong Agricultural University, Wuhan 430070, China; Hubei Engineering Technology Research Center for Aquatic Animal Diseases Control and Prevention, Wuhan 430070, China.
Institute of Parasitology, Biology Centre, Academy of Sciences of the Czech Republic, Branišovská 31, 370 05 České Budĕjovice, Czech Republic.
Int J Parasitol. 2019 Jun;49(7):523-530. doi: 10.1016/j.ijpara.2019.02.009. Epub 2019 May 9.
Genera Myxobolus Bütschli, 1882 and Henneguya Thélohan, 1892 (Myxobolidae) are specious myxozoan genera. They comprise nearly half of overall known myxozoan species diversity. A typical spore feature of Henneguya is the presence of two caudal appendages of the spore valves, which distinguishes them from species of the genus Myxobolus. Several Myxobolus spp., however, were reported to show aberrant spores with Henneguya-like caudal appendages. We found such aberrant spores in Myxobolus tsangwuensis and Myxobolus wulii. We studied the ultrastructure of M. wulii and Myxobolus oralis spores with caudal appendages by transmission electron microscopy (TEM). TEM of these aberrant spores revealed that their caudal appendages have the same ultrastructure as the appendages of Henneguya spp. Small caudal appendages of M. wulii spores observed only on TEM suggested that this character may be often overlooked and more Myxobolus species potentially have the ability to express the caudal appendages on the myxospore. In order to trace the evolution of this character, we performed broad phylogenetic analysis of all species of the family Myxobolidae which are available in GenBank including nearly 300 taxa. We found at least eight independent evolutionary origins of spores with two appendages, three origins of a single appendage and 12 apparent secondary losses of the spore projections. Therefore, genus Henneguya with typical two-tailed myxospores is polyphyletic, however a majority of its species has a common ancestor and groups in the second largest subclade of the Myxobolus clade. We also mapped the biological characteristics (host, site of infection and environment) of Myxobolidae species on the phylogenetic tree. We revealed an evident host-associated evolutionary pattern in all parts of the Myxobolus clade with a distinct and species-rich subclade containing almost exclusively species infecting species of the Order Cypriniformes.
种类 Myxobolus Bütschli，1882 和 Henneguya Thélohan，1892（粘孢子虫科）是多态粘孢子虫属。它们构成了已知粘孢子虫物种多样性的近一半。Henneguya 物种的一个典型孢子特征是孢子瓣上存在两个尾附属物，这将它们与 Myxobolus 属的物种区分开来。然而，有报道称一些 Myxobolus spp. 表现出具有 Henneguya 样尾附属物的异常孢子。我们在 Myxobolus tsangwuensis 和 Myxobolus wulii 中发现了这种异常孢子。我们通过透射电子显微镜（TEM）研究了具有尾附属物的 M. wulii 和 Myxobolus oralis 孢子的超微结构。这些异常孢子的 TEM 显示，它们的尾附属物具有与 Henneguya spp. 相同的超微结构。仅在 TEM 上观察到的 M. wulii 孢子的小尾附属物表明，这个特征可能经常被忽视，并且更多的 Myxobolus 物种可能具有表达孢子尾附属物的能力。为了追踪这个特征的进化，我们对 GenBank 中所有粘孢子虫科物种进行了广泛的系统发育分析，包括近 300 个分类群。我们发现至少有 8 个独立的具有两个附属物的孢子进化起源，3 个单附属物的起源和 12 个孢子突起的明显二次丢失。因此，具有典型双尾孢子的 Henneguya 属是多系的，然而，它的大多数物种具有共同的祖先，并在 Myxobolus 支系的第二大亚支中聚集。我们还在系统发育树上绘制了粘孢子虫科物种的生物学特征（宿主、感染部位和环境）。我们揭示了在 Myxobolus 支系的所有部分都存在明显的宿主相关进化模式，一个明显的和物种丰富的亚支包含几乎完全由感染鲤形目物种的物种组成。
