Aprimary Research On The Genetic Divergence And Demographic History Of Luciogobius Guttatus

When people see a strange species, it is often the first to measure its appearance. But due to geographical isolation and selection pressure between closely related species or lineages,significant differentiation at the molecular level may occur prior to the morphological differences, and these morphologically hidden unit may indicates the formation of new species. DNA sequences provide irreplaceable information which helps uncovering the evolutionary history and genetic boundary of such approximated units.In this study, DNA sequences were used to clarify the systematics of the flat-head goby(Luciogobius guttatus, Gobionellinae), an intertidal dweller in the stony coasts of East Asia.Former researches have shown that there are three lineages(A, B, C) of Luciogobius guttatus in the Japan Archipelago. However, previous studies in China focusing on L. guttatus are mainly limited to morphological measuring and survey records.Based on both mtDNA(16S r RNA, COI, CYTB, mitochondrial control region) and nuc DNA(two introns: in417 and in177, and one exon of RYR3), this study reports the cryptic diversity of their counterparts in northern China from the aspect of molecular systematics and population genetics, which has found that the latitudinal distribution of lineage A(southern)and C(northern) of is affected by Mountain Laoshan. Lineage A and C can be sympatric in both China and Japan, while lineage B has only been identified on the southwestern coasts in Japan. Known from published molecular data, the origin area of L. guttatus is deducted to be the southeastern coasts of the Sea of Japan, where the lineages begun to spread with the opening of the Sea of Japan in the inter-glacial period. Due to the lack of fossil calibration,the evolutionary history is reconstructed with a relaxed molecular clock. Results suggest lineage A is much older than previously thought, as roots back to the late Miocene; lineage B(compared to lineage C) is more similar to the ancestral lineage A, but these two inner taxa(lineage B and C on mitochondrial gene trees) are far separated geologically. On the other hand, although the lineages identified by mtDNA match those identified by nuc DNA, the topology of the clades can be different: lineage A always clades with other species first whenCYTB is used for a ML tree, and in other cases all three lineages of L. guttatus can be monophyletic. Further analysis indicates adaptational differentiation between lineage A and C on different genes. Moreover, a rare non-neutral non-synonymous mutation and more binding motifs were identified in lineage C, in comparison with lineage A. Being opposite to expectation, introns are conserved and in177 is not informative to identify a lineage in this study. Furthermore, the last glacial maximum(LGM) is a key event promoting the expansion,recovery and divergence of the populations of L. guttatus. Nonetheless, the reactions to the LGM are different in different lineages: in terms of divergence between population in China and Japan, lineage C is leading lineage A with a clearer phylogenetic pattern, and has experienced stronger bottleneck before the LGM.Summed up, these results render the molecular basis for the conservation of L. guttatus on the coasts of northern China.