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228 <strong>Zoological</strong> <strong>Studies</strong> 51(2): 222-231 (2012) in haplotype b. Haplotypes e and g were shared by all 3 morphospecies (Fig. 5, Table 1). We reconstructed the phylogenetic trees by including both our sequences and downloaded sequences, and obtained NJ and MP phylogenetic trees with similar tree structures (Fig. 6). Haplotypes a-g from Taiwan were all placed in the same group. DISCUSSION DNA barcoding can be helpful in species identification within cryptic species groups (Hebert et al. 2004, Belyaeva and Taylor 2009). In general, sequence divergences are much lower among individuals of a species than between closely related species. For example, congeneric species of moths exhibit an average sequence divergence of 6.5% in the mitochondrial COI gene, whereas divergences among conspecific individuals average only 0.25% (Moore 1995, Hebert et al. 2004). Similar values were obtained in birds, with intraspecific divergences of COI averaging 0.27%, whereas congener divergences averaged 7.93% (Hebert and Stoeckle et al. 2004). Among 1781 congeneric species pairs of crustaceans, only 1.3% had COI gene divergences of < 2%, 13.4% had COI gene divergences ranging 4%- 8%, and 81.8% had COI gene divergences ranging 8%-32% (Hebert et al. 2003). In a study of the scale of intercontinental divergence for the cladoceran genus Daphnia, Adamowicz et al. (2009) observed a pairwise sequence divergence within the D. obtusa complex of up to a maximum of 16.9%, with divergences of up to 19% within the D. longispina complex. In our study, S. serrulatus and S. heilongjiangensis showed 14%- 16% COI divergence from each other and from Simocephalus sensu stricto. These interspecific differences were similar to most crustaceans (Hebert et al. 2003). Based on the morphological differences described by Orlova-Bienkowskaja (2001), 3 species - S. vetulus, S. vetuloides, and S. mixtus - were previously recorded in Taiwan. Indeed, our morphometric analysis of the valve shape revealed a significant difference between S. vetulus and S. mixtus from Taiwan, which appeared to support their taxonomic status as different species. However, when all 3 putative species were included in the analysis, the PCA did not separate S. vetulus, S. vetuloides, and S. mixtus from one another, as they formed a morphological continuum. This is consistent with a single morphologically variable species. Furthermore, differences in valve shape among S. vetulus, S. vetuloides, and S. mixtus collected in Taiwan were not associated with genetic variations. The genetic distances in COI among them were very small (0.6%-0.8%), a divergence level that corresponds Hap d: S. vetuloides, S. mixtus, S. vetulus 57 69 99 Hap e: S. vetuloides, S. mixtus, S. vetulus Hap g: S. vetuloides Hap f: S. vetulus Hap a: S. vetuloides, S. mixtus, S. vetulus 99 Hap b: S. vetuloides, S. mixtus 71 Hap c: S. vetuloides 99 Hap k: S. serrulatus Hap l: S. serrulatus 86 99 99 79 Hap h: S. heilongjiangensis Hap i: S. heilongjiangensis Hap j: S. heilongjiangensis Daphnia similoides Daphnia similoides Diaphanosoma dubium 0.02 Fig. 4. Phylogenetic tree for Simocephalus species in Taiwan, derived using the Neighbor-joining (NJ) method based on mitochondrial (mt)DNA cytochrome oxidase subunit I (COI) sequences. The numbers indicate support values for 1000 bootstrap calculations.
Young et al. – Study of Simocephalus from Taiwan 229 scC-1 scA-2 bs-1 Hap d sf-1 ha-5 scD-1 scf-1 Hap a dh-1 hs3-1 dgA-1 khB-4 dgB-1 Hap e dd-3 dy-2 Hap f khC-5 mn-2 dd-1 tt-2 Hap b scE-3 gA-1 hs3-3 1j-2 gs-1 Hap g Hap c Fig. 5. Dorsal valve shapes of different haplotypes belonging to Simocephalus vetulus, S. vetuloides, and S. mixtus. Haplotypes a, b, e, and g have different valve shapes with large-scale variations. Hap d ( * ) Hap d ( * ) 62 Hap a ( * ) Hap a ( * 99 95 ) Hap b ( * ) Hap b 63 77 ( * 75 ) Hap c ( * ) Hap c ( * ) Simocephalus vetulus (+) Simocephalus vetulus (+) 99 100 Simocephalus cf. punctatus (#) 85 Simocephalus cf. punctatus (#) 97 66 Hap g ( * ) Hap g 73 ( * ) 87 Hap e ( * ) Hap e ( * ) Hap f ( * ) 99 100 Hap f ( * ) 0.02 * : Taiwan +: UK #: Mexico and Guatemala *: Taiwan +: UK #: Mexico and Guatemala 20 78 69 Simocephalus punctatus (#) Simocephalus cf. exspinosus (#) Simocephalus cf. exspinosus (#) Simocephalus cf. mixtus (#) Simocephalus cf. mixtus (#) 63 Simocephalus punctatus (#) Simocephalus cf. exspinosus (#) Simocephalus cf. exspinosus (#) Simocephalus cf. mixtus (#) Simocephalus cf. mixtus (#) Hap j ( * ) Hap j ( * ) 62 100 Hap k ( * ) 99 Hap k ( * ) Hap l ( * ) Hap l ( * ) Hap i ( * ) 76 Hap i 92 ( * ) 100 Hap h ( * ) 99 Hap h ( * ) Simocephalus serrulatus (#) Simocephalus serrulatus (#) D. dubium ( * ) D. similoides ( * ) D. similoides ( * ) D. dubium ( * ) Fig. 6. Reconstructed phylogenetic trees of Simocephalus. Sequences from GenBank were included in this analysis: S. vetulus (accession no., DQ889172) from the UK, S. cf. punctatus (EU702310 and EU702282) from Mexico and Guatemala, S. cf. exspinosus (EU702296 and EU702279) from Mexico and Guatemala, S. cf. mixtus (EU702305 and EU702281) from Mexico and Guatemala, and S. serrulatus (EU702312) from Mexico and Guatemala. Both the Neighbor-joining (NJ) and maximum-parsimony (MP) trees shared similar branching structures. Haplotypes a-f from our study were all grouped together.
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ISSN: 1021-5506 Zoological Studies
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