Sinogastromyzon sichangensis is a hillstream loach endemic to the upper Yangtze River, China. It is unclear whether this fish lives in a very restricted area or may be dispersed over a long distance. In the present study spatial connectivity of populations of S. sichangensis was investigated based on 343 individuals collected from 12 sites of Chishui River and employing 22 microsatellite loci. The results of genetic diversity analysis showed that observed heterozygosity (HO) and polymorphism information content (PIC) ranged from 0.5653 to 0.6999 and 0.8513 to 0.8819, respectively. Population structure analysis suggested that S. sichangensis had an unclear genetic structure. AMOVA showed that 69.36% of genetic variation was attributed to differentiation within individuals and all the pairwise genetic differentiation indices (FST) were low (mean FST = 0.0344), indicating weak differentiation among these populations. Estimation of gene flow showed frequent flow among populations, and contemporary levels (mean contemporary migration rate, mc = 0.0131) were approximately equal to historical levels (mean historical migration rate, mh = 0.0147). Individual relatedness analysis revealed a high level of sibship within and among different populations. The frequent gene flow and widespread sibship were due to S. sichangensis laying drifting eggs which travel for a long distance until hatching, after which the juveniles or adults migrate upstream. The results of unclear geographic structure and frequent exchange also indicate that it is necessary to decrease the negative impacts of anthropogenic activities on the connectivity of rivers to protect the migration routes of S. sichangensis.
Keywords: connectivity; gene flow; genetic diversity; hillstream loaches; microsatellite; relatedness analysis.