Composition and richness of monogonont rotifers from La Plata River Basin, South America

Abstract: We present here the first study that analyzed the composition and richness of rotifers of the entire La Plata River basin, the second largest in South America, based on simultaneous and standardized sampling. Fifteen large reservoirs and eight river stretches were selected in the upper, middle, and lower portions of the Paraná, Paraguay, and Uruguay Rivers, which are the major rivers of the La Plata basin. We took a total of 86 samples (open water habitats) in 2010. A mean of 27±11 species per sub-basin was found, with the highest richness in the Lower Paraná (41 species), followed by the Paranapanema (40 species) and Lower Uruguay (38 species). Low richness was observed in the Middle Uruguay and Middle Paraná. We found 106 species belonging to 21 families and two orders. The family with the highest number of species was Lecanidae (21), followed by Brachionidae (20), Trichocercidae (9), and Synchaetidae (8). The species with higher occurrences were Conochilus dossuarius, Kellicottia bostoniensis, Keratella americana, Keratella cochlearis and Hexarthra mira. New occurrences of rotifers were registered for Brazil (Colurella adriatica), São Paulo State (Enteroplea lacustris), and Argentina (Gastropus hyptopus, Harringia rousseleti and Lecane thienemanni). Spearman correlation between the number of species and physical and chemical variables demonstrated positive correlation with chlorophyll and temperature, and negative correlation with dissolved oxygen. We extend the distribution list for some native (Lecane ludwigii) and non-native species of rotifers (K. bostoniensis). We also list the monogonont rotifer species found at the sampling stations.摘要：本研究首次基于同步标准化采样方案，对南美第二大流域——拉普拉塔河（La Plata River）流域全境的轮虫群落组成与物种丰富度开展系统性分析。研究选取构成拉普拉塔河水系主干的巴拉那河、巴拉圭河与乌拉圭河三大支流的上、中、下游区段，共设置15座大型水库与8处河流河段作为采样位点。2010年共计采集86份开阔水体生境样本。各次级流域（sub-basin）的平均物种数为27±11，物种丰富度最高的区域为下巴拉那河（41种），其次为巴拉那帕内马河（Paranapanema，40种）与下乌拉圭河（38种）；中乌拉圭河与中巴拉那河的物种丰富度相对较低。本次研究共记录到隶属于21科、2目的106种轮虫，其中物种丰度最高的类群为镜轮科（Lecanidae，21种），依次为臂尾轮科（Brachionidae，20种）、刺足轮科（Trichocercidae，9种）与聚花轮科（Synchaetidae，8种）。出现频率最高的轮虫物种依次为多室聚花轮虫（Conochilus dossuarius）、波士顿凯轮虫（Kellicottia bostoniensis）、美洲龟甲轮虫（Keratella americana）、螺形龟甲轮虫（Keratella cochlearis）与奇异六腕轮虫（Hexarthra mira）。本研究新增多项轮虫物种的新分布记录：在巴西境内记录到亚得里亚斜管轮虫（Colurella adriatica），在圣保罗州记录到湖生肠轮虫（Enteroplea lacustris），在阿根廷境内记录到腹足轮虫（Gastropus hyptopus）、哈林轮虫（Harringia rousseleti）与蒂曼氏镜轮虫（Lecane thienemanni）。对轮虫物种数与理化环境因子开展斯皮尔曼（Spearman）相关性分析后发现，物种丰富度与叶绿素含量及水温呈正相关，与溶解氧含量呈负相关。本研究还更新了部分本土轮虫（路德氏镜轮虫，Lecane ludwigii）与外来轮虫（波士顿凯轮虫，K. bostoniensis）的分布名录。此外，本研究还列出了各采样站点所检出的单巢纲轮虫（monogonont rotifer）物种。