Search

Sympatric speciation means that new species ignore the absence of geographic isolation. Compared with allopatric speciation, there are more blanks that need to be filled because of rarity. This paper analyzes the researches about angiosperms sympatric speciation in the past ten years, and focuses on the origin factors and reproductive isolation. Judging seems to be more difficult because of the uncertain historic geographic and close relationship between related species. The origin can be divided into ecological factors that mean destructive selection from special niches and gene factors that include hybridization and polyploids. The former drives ancestor into subgroups with different preferences and strengthened by resource competition and co-evolution. The latter creates species faster in places where the allopolyploid has most contribution, the homoploid hybrid and autopolyploid seem to be wide, but insignificant to the speciation. Similarly, reproductive isolation can be divided into the prezygotic and the postzygotic. The former plays a leading role, with more important flowering isolation and pollinator isolation, while the pollen competition, gamete incompatibility and the later that includes hybrid defect such as abortion, infertility and decline are slight and will accelerate the evolution of prezygotic as well as selfing because of high reproductive costs. In short, sympatric speciation requires the cooperation of various factors and the reproductive isolation can conexist with gene flow, which is driven by the niche competition. Especially when the destructive selection is strong enough, sympatric speciation can continue even if the gene flow is frequent. [ABSTRACT FROM AUTHOR]

Sarcocheilichthys nigripinnis is a small cyprinid fish widely distributed in East Asia, and it has been widely used in biogeographic analyses of freshwater fishes in China. In the present study, 142 S. nigripinnis individuals from 20 sampling sites in eight river systems were collected to investigate its phylogeography and genetic variations.. Populations from the Yellow River represent northern clade and all others represent southern clade. The results showed that 56 haplotypes were identified as mitochondrial DNA (mtDNA) Cyt b gene of 1 140 bp length. Relatively high haplotype diversity (h=0.971) and low nucleotide diversity (π=0.0212) were detected, and the estimated average genetic distance was 2.2%. Moreover, a neighbor-joining(NJ)tree revealed seven strongly supported lineages. Populations from the Yellow River were located at the basal position, whereas the remaining populations were more derived. Our results indicate that S. czerskii might have been evolved from S. nigripinnis in the Yellow River ~1.03 Ma. Based on the phylogeographical analysis of S. nigripinnis, we also suggest that vicariance, following mountain uplift and drainage isolation, plays an important role in producing evolutionary lineage differentiations. Moreover, molecular dating estimated that the divergence time of S. czerskii could be dated back to 0.95~3.92 Ma. Mismatch distribution analysis and neutrality tests also suggested the recent demographic expansions of S. nigripinnis populations, and that the effects of Pleistocene climatic changes could be a vital factor of the population dynamics of S. nigripinnis.