Molecular Phylogenetics And Population Genetic Structure Of Genus Pelteobagrus (Teleostei, Bagridae)

In order to interpret the methods and significance of the present study, we reviewed briefly the fundamental principle of molecular systematics, research methods, phylogenetic analysis, molecular phylogeography, neutrality theory and molecular evolution as well as the minimum spanning network. Also we briefly reviewed the phylogenetic investigation progress of Pelteobagrus.Genus Pelteobagrus, belonging to Bagridae in Siluriformes, is endemic to East Asia. Among them, five species distributed in China, are P. fulvidraco, P. intermedius, P. eupogon, P. vachelli and P. nitidus. To date published morphological and molecular phylogenetic relationships of Pelteobagrus are part congruent, and there is few genetic population structure investigation on this genus. We used mtDNA ND4 gene sequences to clarify the existing gaps in the phylogenetic relationships and genetic variability as well as population genetic structure of these species.Mitochondrial DNA ND4 (plus two 3' flanking tRNAs: Histidine tRNA, Serine tRNA) gene sequence variations of these five species from different drainages were studied in the present study. Wallago attu is designated as outgroup in the present study. About 702 base pair sequences were obtained through PCR amplification. Sequence variation analysis was conducted using MEGA2.1 software. The parsimony informative sites were 144 bp and occupied 20.5%, and 206 bp, occupy 29.3% for the variable sites. The Kimura's 2-Parameter sequence divergences were calculated and molecular phylogenetic trees were reconstructed by using the neighbor-joining (NJ) and maximum parsimony (MP) methods as well as Bayesian inference. The results show that (1) in the three molecular cladogram, P. vachelli forms a sister group with P. nitidus; P. fulvidraco, P. intermedius and P. eupogon form a monophyletic group; (2) the phylogenetic position of P. fulvidraco, P. eupogon, and P. intermedius are not recognized.All the specimens were collected from the mainland China. Among them, 60 individuals of P. fulvidraco from 19 localities, 27 individuals of P. nitidus from 7 localities, 15 individuals of P. vachelli from 7 localities, and 13 individuals of P. eupogon from 2 localities. From the 60 individuals of P. fulvidraco, a total of 23 haplotypes are found and haplotype F2 was shared among almost all the localities. And 19 haplotypes for P. nitidus; 11 unique haplotypes in individuals of P. vachelli; and 7 haplotypes for the 13 individuals of P. eupogon, indicating a high degree of polymorphism of the four species. The statistic of molecular genetics and population genetics analyzed using ARLEQUIN 2.000. We found high haplotype and nucleotide diversity in the population of P. vachelli. In contrast, the higher haplotype diversity and the lower nucleotide diversity were in the population of P. fulvidraco, P. nitidus, and P. eupogon. P. fulvidraco had a unimodal mismatch distribution at the left side of the graph, and P. nitidus had a unimodalmismatch distribution, but both P. vachelli and P. eupogon had multimodal mismatch distribution. Based on the relationship t =2ut and the maturity, the expansion events most possibly occurred between 414 000 and 692 000 years ago in the P. fulvidraco population and 514 000 and 857 000 years ago in the ￡ nitidus populaton. The results show that (1) P. vachelli showed a higher genetic diversity, whereas P. fulvidraco, P. nitidus and P. eupogon showed a lower genetic diversity; (2) minimum spanning network, the distribution of haplotypes and haplotype divergences represent a demographic expansion from a single ancestral lineage of P. fulvidraco between 414 000 and 692 000 years ago. For the statistics of other neutrality tests, Tajima's D (-2.09, P=0.003), Fu's Fs (-8, P=0) and SSD (0.0032, P=0.4310) are all significant for the P. fulvidraco; (3) there might be a population expansion of P. nitidus about 514 000—857 000 years ago. Fu's Fs (-11.84, P=0.001) and SSD (0.0068, P=0.1870) are all significant for the P. nitidus. (4) In contrast, P. vachelli and P. eupogon may have experienced a long evolutionary history in a large stable population.