RESULTS: We used 43,310 SNPs to infer the population structure, evidence of local adaptation and sources of introduction. The overall genetic differentiation of this species was low. The native populations were differentiated into three genetic clusters, corresponding to the Yangtze, Pearl and Heilongjiang River Systems, respectively. The populations in Malaysia, India and Nepal were introduced from both the Yangtze and Pearl River Systems. Loci and genes involved in putative local selection for native locations were identified. Evidence of both positive and balancing selection was found in the introduced locations. Genes associated with loci under putative selection were involved in many biological functions. Outlier loci were grouped into clusters as genomic islands within some specific genomic regions, which likely agrees with the divergence hitchhiking scenario of divergence-with-gene-flow.
CONCLUSIONS: This study, for the first time, sheds novel insights on the population differentiation of the grass carp, genetics of its strong ability in adaption to diverse environments and sources of some introduced grass carp populations. Our data also suggests that the natural populations of the grass carp have been affected by the aquaculture besides neutral and adaptive forces.
Methods: In the present study, displacement loop (D-loop) sequences were used to evaluate the genetic relationship and diversity of seven tilapia populations that are widely cultured in China; this was done specifically to speculate on the maternal ancestry of red tilapia strains. Three red tilapia varieties of Oreochromis ssp., Taiwan (TW), Israel (IL), and Malaysia (MY) strains and other populations, including O. aureus (AR), O. niloticus (NL), O. mossambicus (MS), and the GIFT strain of O. niloticus, were collected and analyzed in this study.
Results: A total of 146 polymorphic sites and 32 haplotypes of D-loop sequences were detected among 332 fish and four major haplotypes were shared among the populations. The TW and NL populations had a greater number of haplotypes (20 and 8, respectively). The haplotype diversity (Hd) and nucleotide diversity (π) of each population ranged from 0.234 to 0.826, and 0 to 0.060, respectively. The significant positive Tajima's D value of neutral test were detected in the NL, IL, and MY populations (P 0.05). The nearest K2P genetic distance (D = 0.014) was detected between the MS and TW populations, whereas, the farthest (D = 0.101) was found between the GIFT and AR populations. The results from the molecular variance analysis (AMOVA) showed that there was an extremely significant genetic variation observed among the populations (P