Population structure of Nouelia insignis (Asteraceae), an endangered species in southwestern China, based on chloroplast DNA sequences: recent demographic shrinking.

Nouelia insignis, an endangered species, is distributed in the Jinsha and Nanpan drainage areas in southwestern China. In this study, we examined the genetic diversity and population structure based on the sequences of the cpDNA rpL 16 intron. Low levels of genetic variation were detected within all populations of the endemic species. A gene genealogy of 11 haplotypes recovered two major lineages I and II, with haplotypes H1 and H6 nested as interior nodes, respectively. Haplotype H1 was widespread in all populations, while haplotype H6 was restricted to populations southern of the Jinsha River. Low levels of genetic differentiation were detected, as most F (st) values between populations were zero. This result, however, contradicts previous studies based on allozymes and fingerprinting. Genetic analyses suggested that coancestry due to low evolutionary rates resulted in the lack of geographical subdivision. Molecular dating estimated that the two lineages split about 3.224 MYA (95% CI 1.070-6.089 MYA). Maintenance of ancestral polymorphisms was possibly attributable to a long-standing large effective population size until recently. Postglacial demographic expansion was supported by a unimodal mismatch distribution and star-like phylogenies.