Data from: Morphological and taxonomic demarcation of Brachionus asplanchnoidis Charin within the Brachionus plicatilis cryptic species complex (Rotifera, Monogononta)

Three well-defined groups, consisting of 15 species, have recently been ascribed to organisms historically identified as the Brachionus plicatilis species complex. One of these groups, the Large-clade is composed of two named species (Brachionus plicatilis s.s. and Brachionus manjavacas) and two species identifiers (B. 'Nevada' and B. 'Austria'). B. 'Austria' has been confirmed to be B. asplanchnoidis. As no type specimen exists for this species, and the original taxonomic description is lacking in detail, we give a detailed account of this species using material from Obere Halbjochlacke in Austria where B. 'Austria' was first identified genetically. Our analysis of B. asplanchnoidis populations were of global scope; an approach that revealed a great degree of morphological variability. However, combining aspects of both the dorsal and ventral surfaces clearly discriminated B. asplanchnoidis from the rest of the Large type members. This approach may prove useful in taxonomic studies of other cryptic species with relatively few morphological features. We also observed a geographic pattern of genetic divergence within B. asplanchnoidis. Average uncorrected COI divergences for a 554-bp fragment of the COI gene ranged from 3.9% within species to 17.5% between species of the Large-clade, and indicate deep divisions within the cryptic species complex.

近期，3个界定清晰的类群（共涵盖15个物种）被归入历史上被鉴定为褶皱臂尾轮虫物种复合体（Brachionus plicatilis species complex）的生物类群中。其中一个类群——大支系（Large-clade）——包含2个已正式命名的物种（狭义褶皱臂尾轮虫（Brachionus plicatilis s.s.）与曼贾瓦卡斯轮虫（Brachionus manjavacas）），以及2个暂未定名的物种分类单元（B. 'Nevada'与B. 'Austria'）。现已确认B. 'Austria' 即为扁平臂尾轮虫（B. asplanchnoidis）。由于该物种尚无模式标本（type specimen），且原始分类记述细节匮乏，我们利用奥地利Obere Halbjochlacke（首次通过遗传学手段鉴定出B. 'Austria' 的采样位点）的实验材料，对该物种进行了详细的分类记述。我们针对扁平臂尾轮虫（B. asplanchnoidis）开展了全球范围的种群分析，该研究揭示了该物种极高的形态变异程度。不过，结合背腹两面的形态特征，可将扁平臂尾轮虫与大支系的其余物种清晰区分开来。该分类鉴定方法或可推广应用于其他形态特征匮乏的隐存物种（cryptic species）的分类学研究。我们还在扁平臂尾轮虫种群内部观测到了遗传分化的地理分布模式。针对细胞色素C氧化酶亚基I（COI）基因554碱基对（bp）片段的平均未校正COI遗传分化率，在大支系内的物种内部为3.9%，物种间则为17.5%，该结果表明该隐存物种复合体内部存在显著的深层分化。