[Age structure and genetic diversity of Homatula pycnolepis in the Nujiang River basin].

This study examined the age structure of the Loach, Homatula pycnolepis through the otolith growth rings in 204 individual specimens collected from the Xiaomengtong River of the Nujiang River (Salween River) basin in April, 2008. There were only two different age classes, 1 and 2 years of age-no 3 year olds were detected. The age structure of H. pycnolepis was simple. The complete mitochondrial DNA cytochrome b gene sequences (1140) of 80 individuals from 4 populations collected in the Nujiang River drainage were sequenced and a total of 44 variable sites were found among 4 different haplotypes. The global haplotype diversity (Hd) and nucleotide diversity (Pi) were calculated at 0.7595, 0.0151 respectively, and 0, 0 in each population, indicating a consistent lack of genetic diversity in each small population. There was obvious geographic structure in both the Nujiang River basin (NJB) group, and the Nanding River (NDR) group. The genetic distance between NJB and NDR was calculated at 0.0356, suggesting that genetic divergence resulted from long-term isolation of individual population. Such a simple age structure and a lack of genetic diversity in H. pycnolepis may potentially be due to small populations and locale fishing pressures. Accordingly, the results of this study prompt us to recommend that the NJB, NDR and Lancang River populations should be protected as three different evolutionary significant units or separated management units.

[Genetic structure and variation of Glyptothorax laosensis of the Lancang River based on cytochrome b].

The hillstream catfish, Glyptothorax laosensis, is endemic to basin of Lancang River (also known as Mekong River). Genetic variation was detected within and among 8 populations of G. laosensis in Lancang River based on mitochondrial cytochrome b sequences. A total 16 nucleotides sites were detected in 1 138 bp fragment, which defined 15 haplotypes from 129 sequences. The variation level was very low, with mean h=0.299 and π=0.00032, respectively, and no variation was detected in some populations. Hierarchical analysis of molecular variance (AMOVA) showed no significant genetic structuring among populations. The unimodel mismatch distribution of pairwise haplotype difference and the negatively selective neutrality test (Tajima's D=2.3696, P<0.02; Fu's Fs=20.975, P<0.05) suggested that a recent population expansion had occurred.