Confirmation through genetic analysis of the existence of many local phyloclades of the genus Simocephalus (Crustacea, Cladocera) in China

Abstract

Previously, a series of Simocephalus taxa (Cladocera: Daphniidae) from China were described. Most were proposed to be junior synonyms in the last revision of the genus. Using original material from China and data from GenBank, we investigate the biodiversity and phylogeny of Simocephalus using sequences of the cytochrome c oxidase subunit I (COI) and the nuclear 18S genes. In both cases, neighbor-joining, maximum likelihood and Bayesian inference analyses led to highly congruent tree topologies. The grouping of the deeper clades agrees with the inter-generic classification of Orlova-Bienkowskaja (2001). Only the populations of S. serrulatus from Eurasia and North America seem to be closely related, and there are no other shared species between the two continents. Our study unambiguously confirms the existence of many lineages from the subgenera of Simocephalus (Echinocaudus) and Simocephalus s.str. in China, but their morphology needs to be reexamined by taking a wider range of characters (e.g., of female thoracic limbs and adult males) into consideration.

Figure 1. The phylogeny of Simocephalus inferred from mitochondria cytochrome c oxidase subunit I (COI) sequences as a consensus tree formed from trees constructed using Bayesian inference (BI), maximum likelihood (ML), and neighbor-joining (NJ) methods.

Numbers at nodes are as follows: BI posterior probability value multiplied by 100 for legibility, followed by bootstrap values between 0 and 1 from ML and NJ analyses. The scale bar corresponds to 0.1 substitutions per nucleotide position. In the left column, EA indicates Eurasian, and NA indicates North American. A, B, C, D, and E indicate the five subgenera. A: Simocephalus s. str.;B and C: Simocephalus (Echinocaudus); D: Simocephalus (Aquipiculus); and E: Simocephalus (Coronocephalus).

Figure 2. Phylogeny of Simocephalus inferred from 18S sequences as a consensus tree formed from trees constructed using maximum likelihood (ML), Bayesian inference (BI), and neighbor-joining (NJ) methods.

ML bootstrap values between 0 and 1, followed by BI posterior probability value multiplied by 100 for legibility and bootstrap values between 0 and 1 from NJ analyses. The scale bar corresponds to 0.02 substitutions per nucleotide position. A indicates Simocephalus (Echinocaudus), B Simocephalus s. str., D Simocephalus (Aquipiculus), and E Simocephalus (Coronocephalus).

Figure 3. Photographs of living parthenogenetic females of the three morphologically-similar species from China: S. himalayensis microdus (a, d, g, j), S. himalayensis (b, e, h, k), and S. sibiricus (c, f, i, l).

General view (a–c). General view of the postabdomen (d–f). Distal portion of the postabdomen (g–i). Pecten of spines on the postabdominal claw (j–k). Scale bars: 0.5 mm (a–i); 0.01 mm (j–l).