Biodiversity Science ›› 2017, Vol. 25 ›› Issue (5): 549-560.doi: 10.17520/biods.2017045

• Original Papers: Animal Diversity • Previous Article    

Morphology, ontogeny and molecular phylogeny of Euplotes aediculatus Pierson, 1943 (Ciliophora, Euplotida)

Xue Zhang1, Yurui Wang1, Yangbo Fan1, 2, Xiaotian Luo1, Xiaozhong Hu1, Feng Gao1, *()   

  1. 1 College of Fisheries, Ocean University of China, Qingdao, Shandong 266003
    2 School of Civil and Environmental Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen, Guangdong 518055;
  • Received:2017-02-18 Accepted:2017-04-17 Online:2017-06-06
  • Gao Feng E-mail:gaof@ouc.edu.cn

Euplotids are the most complex and highly differentiated group of ciliates. In order to further explore the species diversity of euplotids, the morphology and morphogenesis of Euplotes aediculatus, collected from Small West Lake of Qingdao, were investigated using live observations, protargol, and silver nitrate impregnation. Based on the detailed morphological and morphogenetic data, the small subunit ribosomal rDNA (SSU rDNA) was sequenced for E. aediculatus. The species is characterized by the following features: nine frontoventral, five transverse, two left marginal, and two caudal cirri, eight dorsal kineties, and a silverline system of the double-eurystomus type. The main morphogenetic features during division are as follows: (1) the oral primordium of the opisthe develops de novo within a pouch beneath the cortex, the parental adoral zone of membranelles is entirely kept by the proter; (2) fronto-ventral-transverse cirral anlagen (FVTA) II-VI form cirri in the mode of 3:3:3:2:2; (3) frontal cirrus I/1 of the proter and opisthe is generated from the anlage formed de novo; (4) marginal cirri anlagen are formed de novo; (5) the primary dorsal kinety anlagen are from the dedifferentiation of several bristles in the middle of each parental dorsal kinety; (6) the right-most two dorsal kinety anlagen and parent dorsal kineties contribute to two caudal cirri for the proter and the opisthe, respectively. All of these features showed the high conservation of the ontogenetic process in the genus Euplotes. Sequence comparison and phylogenetic analyses based on SSU rDNA revealed a close relationship among Euplotes aediculatus, E. eurystomus, E. amieti, and E. woodruffi, which is consistent with their similar morphology.

Key words: ciliates, Euplotes aediculatus, morphology, morphogenesis, phylogeny, small subunit ribosomal rDNA (SSU rDNA)

Fig. 1

Morphology of Euplotes aediculatus in vivo, after protargol and silver nitrate impregnation. A, Ventral view of a representative individual; B and C, Ventral (B) and dorsal (C) view of the infraciliature and nuclear apparatus; D and E, Silverline system on ventral (D) and dorsal side (E); AZM, Adoral zone of membranelles; CC, Caudal cirri; CV, Contractile vacuole; FVC, Frontoventral cirri; Ma, Macronucleus; MC, Marginal cirri; PM, Paroral membrane; TC, Transverse cirri. Scale bar = 100 µm."

Fig. 2

Morphology of Euplotes aediculatus. A-E, Photomicrographs in vivo; F and G, Photomicrographs after protargol; H and I, Photomicrographs after silver nitrate impregnation. A, Ventral view of a representative individual, arrow points to collar; B and C, Ventral views, showing different body shapes, arrow in picture B points to contractile vacuole, arrowheads in picture B point to ribs in the back; D, Dorsal view, showing the cortical granules arranged around the dorsal cilia; E, Posterior portion of an individual, showing the caudal cirri (arrows) and the left marginal cirri; F and G, Ventral (F) and dorsal (G) view of the infraciliature and nuclear apparatus; H and I, Silverline system on ventral (H) and dorsal side (I), arrow in picture H points to contractile vacuole. Scale bar = 100 µm."

Table 1

Morphometric characterizations of Euplotes aediculatus from Small West Lake of Qingdao based on protargol-stained specimens"

特征 Character 最小值
Minimum
最大值
Maximum
平均值
Mean
中值
Median
标准差
Standard
deviation
变异系数
Coefficient of variation
个体数
Number
of cells
体长 Length of body (μm) 115 142 128.3 129 7.25 5.7 20
体宽 Width of body (μm) 76 101 92.2 93.5 6.28 6.8 20
口区长 Length of adoral zone (μm) 79 98 86.3 86.5 4.74 5.5 20
口围带小膜数目 Number of adoral membranelles 47 55 51.1 51.5 1.90 3.7 20
额腹棘毛数目 Number of frontoventral cirri 9 9 9 9.0 0 0 19
横棘毛数目 Number of transverse cirri 5 5 5.0 5.0 0 0 20
缘棘毛数目 Number of marginal cirri 2 2 2.0 2.0 0 0 20
尾棘毛数目 Number of caudal cirri 2 2 2.0 2.0 0 0 20
背触毛列数 Number of dorsal kineties 8 8 8.0 8.0 0 0 20
中央背触毛列毛基体数目
Number of dikinetids in mid-dorsal kinety
21 26 21.9 21.0 1.36 6.2 20
最左侧背触毛列毛基体数目
Number of dikinetids in the leftmost dorsal kinety
15 23 18.5 18.0 1.73 9.4 20

Fig. 3

Photomicrographs of Euplotes aediculatus during morphogenesis after protargol impregnation. A, Ventral view of an early divider, showing the oral primordium in opisthe, arrowheads mark the frontal-ventral-transverse cirral streaks of both dividers; B, Ventral view of an early-middle divider, arrowheads show the differentiation of frontal-ventral-transverse cirral anlagen, arrows marks the marginal anlagen; C, Ventral view of a mid-stage divider, arrowheads demonstrate the leftmost frontal cirrus (I/1) in both proter and opisthe, arrows marks the differentiation of marginal anlagen; D, Dorsal view of an early-middle divider, arrowheads show the formation of dorsal kineties anlagen; E, Ventral view of another mid-stage divider, arrowheads show the differentiation of frontal-ventral-transverse cirral anlagen almost complete, arrows point to the new marginal cirri of both daughter cells; F, Ventral view of a late divider, noting the macronucleus become a short strand, arrowheads show the transverse cirri, arrows mark the leftmost frontal cirri (I/1); G, Dorsal view of another late divider, arrowheads show the newly formed caudal cirri in the proter; H, Ventral view of a last stage divider, showing cirri almost in their final position and the division of the macronucleus. DKA, Dorsal kineties anlagen; LMC, Left marginal cirri; Ma, Macronucleus; OP, Opisthe’s oral primordium; UMA, Undulating membrane anlagen. Scale bar = 70 µm."

Fig. 4

Maximum likelihood (ML) tree based on small subunit ribosomal DNA sequences. Newly characterized sequence in this study is shown in bold. The numbers at the nodes represent the support values of ML/Bayesian inference (BI). Fully supported (100/1.00) branches are marked with solid circles. Asterisks reflect the disagreement between ML and BI. All branches are drawn to scale. The scale bar corresponds to five substitutions per 100 nucleotide positions."

Fig. 5

Unmatched sites from SSU rDNA sequence alignment of seven Euplotes aediculatus populations and one E. eurystomus population. Numbers indicate the positions of nucleotides in the alignment, missing sites are represented by dashes (-), and matching sites are marked with dots (.)."

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