| Protosalanx hyalocranius is an economically- important annual small fish endemic to East Asian with anadromous and fresh-water lacustrine ecotypes. In recent years, due to the impact of natural and anthropogenic factors, the endemic resources rapidly depleted, meanwhile nationalwide transplanting of P. hyalocranius have cuased mixture of stocks from various water bodies, increasing the difficulty of effective management and conservation of P. hyalocranius.In this study, genetic variation in P. hyalocranius were analyzed using complete mt DN A C ytochrome b sequences(1141bp) in 180 individuals sampled from 9 localities in 6 river systems throughout C hina to provide the genetic background for the development of better measures to effectively protect and sustainable exploit the germplasm.The results were as following:1. In all, 26 variable sites(including 10 single variable sites and 16 parsimony informative sites) resulted in 27 haplotypes. Haplotype 1, 5, 6, 14 are the most common haplotypes, Haplotye 1 were distributed in all the river basin. Hap5 and Hap6 are mainly distributed in transplanted area.2. Contrasted to relatively high overall genetic diversity(Hd=0.789±0.021, π=0.0014±0.0001), the nucleotide diversity of individual population was much poorer, of which Liao River estuary population harbors the highest genetic diversity(Hd=0.911±0.034,π=0.0018±0.0002), Yangtze River estuary population is poorest(Hd=0.574±0.055,π=0.0006±0.0002). Neither obvious lineage nor geographical structure were found. As far as endemic populations is considered, no significant genetic differentiation were found a mong anadromous Yalu River estuary population, Liao River esturary population, and Yangtze River estuary population(Fst =0.0544-0.0834, p>0.05), meanwhile there existed profound genetic divergence between lacustrine Taihu population and Chaohu population within Yangtze River(Fst =0.1394, P<0.01). While the differentiation between anadromous and lacustrine populations is weak and not significant(FCT=0.009, P>0.05), the differentiation among basins is very weak but is very significant(FCT=0.050,P<0.01). That all indicate that the structure of genetic differentiation of P. hyalocranius is not closely associated with the distribution patterns of water system and life styles, but might be more or less subject to the impact of geographical isolation. Although the formation time of transplanted group is short, genetic differentiation within and among transplanted and originated groups are significant(Fst=0.1111-0.4673, P<0.05),suggesting that they might have been subjected to multiple independent bottlenect events leading to genetic drift and the selection effects.3. Demographic history analysis(significant negative values of neutral test, and the unimodal mismatch distribution, R2 test are 0.080-0.101(P<0.05)) proved that all populations as a whole, Yalu River estuary population, Liao River estuary population, Yangtze River estuary population, have been expanded in recent history, and deduced overall population expansion time was about 80 ka BP-64 ka BP(i.e., during the late Pleistocene), which probably related to the fluctuated sea levels and temperature during the late Pleistocene epochs. Meanwhile not significant negative values of neutral test, R2 test are 0.129-0.161(P>0.05) and the multimodal mismatch distribution, indicated that the population sizes of C hao Lake and Tai Lake population were relatively stable, which might be related to the short formation histories of C hao Lake and Tai Lake.4. As Liao River estuary population harbors the highest nucleotide diversity(π) in the studied areas, it should be protected in priority. Taihu Lake harbors the largest endemic lacustrine population size, it is also very valuable for protection. |
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