Urechis unicinctus is distributed only in Bohai Gulf of China and Korean and Japanese coast. The wild populations of this species have sharply declined in China and Japan. We collected 105 samples from six localities of Bohai Gulf and Korea coast, and investigated genetic diversity and population structure with mitochondrial COI, 16S-rRNA and nuclear 28S-rRNA gene fragments. Genetic diversity of U. unicinctus based on COI sequences was still high (Hd: 0.9595, π: 0.0101), however, 28S-rRNA gene sequences showed low level of genetic diversity (Hd: 0.4084, π: 0.0007). Based on COI sequences, F values between populations ranged from -0.00204 to 0.05210, and 99.12% genetic diversity was contributed by different individuals within population. Both phylogenetic trees and median-joining network did not show clear geographic cluster, haplotypes from different populations were mixed. Our results indicated low level of genetic divergence among different localities of U. unicinctus, and this species should be treated as a whole population among China, Japan and Korea coast during species conservation.
ABSTRACT. Sex-specific DNA markers are useful for studying sexdetermination mechanisms and establishment of monosex populations. Three widely spaced geographical populations (Liangzi, Poyang and Yuni Lakes in China) of blunt snout bream (Megalobrama amblycephala) were screened with AFLPs to search for sex-linked markers. Female and male pools (10 individuals in each pool) from each population were screened using 64 different primer combinations. A total of 4789 genomic fragments were produced, with a mean frequency of 75 bands per primer pair. Three different primer combinations produced putative sex-associated amplifications and were selected for individual screening in the three populations. However, none showed sex specificity when we converted these three markers into sequence characterized amplified region markers and evaluated all the individuals from the three populations.
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