Department of Environmental and Forest Biology, College of Environmental Science and Forestry, State University of New York (SUNY ESF), 1 Forestry Drive, Syracuse, New York 13210.
Division of Science and Mathematics, Eastern Oklahoma State College, Idabel, Oklahoma 74745.
J Parasitol. 2021 Nov 1;107(6):912-922. doi: 10.1645/21-73.
Myxosporean species in the genus Cystodiscus are parasites of amphibians and have been reported from several continents. Typically used for the identification of myxozoans, the spores produced by these species are similar to one another, possessing 2 polar capsules and being ovoid. The number of transverse depressions on the spore can be useful for delineating species, but these can sometimes be difficult to distinguish. In North America, Cystodiscus serotinus and Cystodiscus melleni have been described, and for C. serotinus in particular, numerous reports and a wide range of hosts have been associated with this species. Given the challenges of identifying some of these species, we questioned whether all encounters of Cystodiscus species can be attributed to these 2 described species, or if there may be additional undescribed species or cryptic species. Over 7 yr, 383 amphibians representing 13 species of toads, frogs, and salamanders were collected from sites in Oklahoma and Arkansas. Cystodiscus infections were found in 56 individuals (14.6%). Tissues from these infected individuals were preserved in alcohol for genetic analysis. The small subunit (SSU) and large subunit (LSU) ribosomal RNA genes were partially sequenced and analyzed phylogenetically. Nine distinct SSU sequence types and 7 distinct LSU sequence types were identified. Phylogenetically, sequence types were attributable to C. serotinus, C. melleni, Cystodiscus axonis, and an undescribed species. For the previously described species, there were multiple SSU sequence types: 4 for C. serotinus and 2 for both C. melleni and C. axonis. Phylogenetic patterns were similar for the LSU sequence analysis using a shorter sequence than the SSU, and we propose that the LSU is useful for initial barcoding of Cystodiscus species in any future surveys. In our qualitative assessment of sequence types compared to geography and host species, SSU types C1 and C2 (C. axonis) were only found in Union County, Arkansas, and McCurtain County, Oklahoma, respectively. Also, salamanders were only infected with SSU types B or D (C. melleni), and type B was only found in salamanders. Our finding of C. axonis in North America is notable because this species was described in Australia and is associated with host pathology. Our work reveals that there are cryptic species of Cystodiscus in the United States, one of which may be a pathogen, highlighting the importance of genetic analysis for future surveys of these species.
类孢子虫属的类孢子虫是两栖动物的寄生虫，已在各大洲报道过。这些物种产生的孢子通常用于鉴定粘孢子虫，它们彼此相似，具有 2 个极囊，呈卵形。孢子上的横向凹陷数量对于物种的划分很有用，但有时很难区分。在北美，已经描述了类孢子虫属的 Cystodiscus serotinus 和 Cystodiscus melleni，特别是对于 C. serotinus，已经有许多报告和广泛的宿主与该物种相关。鉴于鉴定这些物种中的一些具有挑战性，我们质疑是否可以将类孢子虫属的所有种都归因于这两种已描述的种，或者是否可能存在其他未描述的种或隐种。在 7 年多的时间里，从俄克拉荷马州和阿肯色州的多个地点收集了代表蟾蜍、青蛙和蝾螈 13 个物种的 383 只两栖动物。在 56 只个体（14.6%）中发现了类孢子虫属感染。从这些受感染的个体中保存的组织用于遗传分析。部分测序了小亚基（SSU）和大亚基（LSU）核糖体 RNA 基因，并进行了系统发育分析。鉴定出 9 种不同的 SSU 序列类型和 7 种不同的 LSU 序列类型。系统发育分析表明，序列类型可归因于 C. serotinus、C. melleni、Cystodiscus axonis 和一个未描述的种。对于先前描述的种，有多种 SSU 序列类型：C. serotinus 有 4 种，C. melleni 和 C. axonis 各有 2 种。LSU 序列分析的系统发育模式与 SSU 相似，我们建议 LSU 对于未来任何调查中的类孢子虫种的初步条形码都很有用。在我们对序列类型与地理和宿主物种的定性评估中，SSU 类型 C1 和 C2（C. axonis）仅在阿肯色州的联合县和俄克拉荷马州的麦柯蒂恩县发现。此外，只有 SSU 类型 B 或 D（C. melleni）感染了蝾螈，而类型 B 仅在蝾螈中发现。我们在北美的发现表明，该物种是澳大利亚的特有种，与宿主病理学有关。我们的工作表明，美国存在隐种的类孢子虫，其中一种可能是病原体，这凸显了遗传分析对于未来这些物种调查的重要性。
