The University of Queensland, School of Biological Sciences, St Lucia, QLD 4072, Australia.
The University of Queensland, School of Biological Sciences, St Lucia, QLD 4072, Australia.
Int J Parasitol. 2021 Nov;51(12):1035-1046. doi: 10.1016/j.ijpara.2021.05.003. Epub 2021 Jun 27.
The trematode superfamily Monorchioidea comprises three families of teleost parasites: the Monorchiidae Odhner, 1911, Lissorchiidae Magath, 1917, and Deropristidae Cable & Hunninen, 1942. All presently known lissorchiid and deropristid life cycles have gastropods as first intermediate hosts, whereas those of monorchiids involve bivalves. Here, we report an unexpected intermediate host for monorchiids; two species of Hurleytrematoides Yamaguti, 1954 use gastropods as first intermediate hosts. Sporocysts and cercariae were found infecting two species of the family Vermetidae, highly specialised sessile gastropods that form calcareous tubes, from two locations off the coast of Queensland, Australia. These intramolluscan infections broadly corresponded morphologically to those of known monorchiids in that the cercariae have a spinous tegument, oral and ventral suckers, a simple tail and distinct eye-spots. Given the simplified morphology of intramolluscan infections, genetic data provided a definitive identification. ITS2 rDNA and cox1 mtDNA sequence data from the gastropod infections were identical to two species of Hurleytrematoides, parasites of butterflyfishes (Chaetodontidae); Hurleytrematoides loi McNamara & Cribb, 2011 from Moreton Bay (south-eastern Queensland) and Heron Island (southern Great Barrier Reef) and Hurleytrematoides morandi McNamara & Cribb, 2011 from Heron Island. Notably, species of Hurleytrematoides are positioned relatively basal in the phylogeny of the Monorchiidae and are a sister lineage to that of species known to infect bivalves. Thus, the most parsimonious evolutionary hypothesis to explain infection of gastropods by these monorchiids is that basal monorchiids (in our analyses, species of Cableia Sogandares-Bernal, 1959, Helicometroides Yamaguti, 1934 and Hurleytrematoides) will all prove to infect gastropods, suggesting a single host switching event into bivalves for more derived monorchiids (17 other genera in our phylogenetic analyses). A less parsimonious hypothesis is that the infection of vermetids will prove to be restricted to species of Hurleytrematoides, as an isolated secondary recolonisation of gastropods from a bivalve-infecting lineage. Regardless of how their use arose, vermetids represent a dramatic host jump relative to the rest of the Monorchiidae, one potentially enabled by their specialised feeding biology.
吸虫的 Monorchioidea 超科包括三种鱼类寄生虫：Monorchiidae Odhner, 1911、Lissorchiidae Magath, 1917 和 Deropristidae Cable & Hunninen, 1942。目前已知的 lissorchiid 和 deropristid 生命周期都以腹足动物为第一中间宿主，而 monorchiid 则涉及双壳类动物。在这里，我们报告了一个意想不到的 monorchiid 中间宿主；两种 Hurleytrematoides Yamaguti, 1954 属吸虫使用腹足动物作为第一中间宿主。在澳大利亚昆士兰州海岸的两个地点，发现两种 Vermetidae 科的腹足动物感染了旋孢子虫和尾蚴，这些腹足动物是高度专门化的固着腹足动物，形成钙质管。这些腹内感染在形态上与已知的 monorchiid 非常相似，因为尾蚴具有刺状外皮、口和腹吸盘、简单的尾巴和明显的眼点。鉴于腹内感染的简化形态，遗传数据提供了明确的鉴定。来自腹足动物感染的 ITS2 rDNA 和 cox1 mtDNA 序列数据与两种 Hurleytrematoides 属寄生虫完全一致，即 Chaetodontidae 蝴蝶鱼寄生虫；Moreton Bay（昆士兰州东南部）和赫伦岛（大堡礁南部）的 Hurleytrematoides loi McNamara & Cribb, 2011 以及赫伦岛的 Hurleytrematoides morandi McNamara & Cribb, 2011。值得注意的是，Hurleytrematoides 属的物种在 Monorchiidae 的系统发育中相对处于基础地位，并且与已知感染双壳类动物的物种形成姐妹谱系。因此，解释这些 monorchiid 感染腹足动物的最简约进化假设是，基础 monorchiid（在我们的分析中，Cableia Sogandares-Bernal, 1959、Helicometroides Yamaguti, 1934 和 Hurleytrematoides 属的物种）都将被证明感染腹足动物，这表明更衍生的 monorchiid（我们的系统发育分析中的 17 个其他属）将经历单一的宿主转换事件进入双壳类动物。一个不太简约的假设是，vermetid 的感染将被证明仅限于 Hurleytrematoides 属物种，这是腹足动物从感染双壳类动物的谱系中孤立地二次重新殖民化的结果。无论它们的用途如何产生，vermetid 相对于 Monorchiidae 的其余部分代表了一个戏剧性的宿主跳跃，这可能是由它们专门的摄食生物学所促成的。
