Phylogeny and divergence times inferred from rps16 sequence data analyses for Tricyrtis (Liliaceae), an endemic genus of north-east Asia.

BACKGROUND AND AIMS

Tricyrtis is a genus of monocots with attractive and sophisticated flower shapes and colours, endemic to north-east Asia. There are 18 known species. The highly restricted geographical distribution of the genus is of great interest in terms of both abiotic (continental drift) and biotic (long-distance dispersal) impacts on monocot plant speciation events and their timing, and of evolutionary patterns of diversification leading to the extant taxa. The aims of this study were to (i) predict the time of speciation (divergence) events at infraspecific levels of Tricyrtis, (ii) estimate the rate of evolution of the genus and (iii) provide information on an excellent plant model system in terms of studying loss of biodiversity or extinction of organisms in the dynamic earth environment.

METHODOLOGY

To investigate the divergence time and evolution rate of Tricyrtis, Bayesian Markov chain Monte Carlo (MCMC) analyses were performed by calculating the mean branch lengths of evolutionary paths based on base substitution variations between rps16 intron nucleotide sequences from the 18 known species.

PRINCIPAL RESULTS

Based upon the relaxed molecular clock model test data, a Bayesian phylogenetic inference tree is presented, and the divergence times and rate of evolution of Tricyrtis were estimated. The analyses also suggest that evolution is occurring at the infraspecific level of the genus in a manner that is not strictly clock bound.

CONCLUSIONS

Continental drift may have been the main speciation process giving rise to the current distribution of the taxa of Tricyrtis. The single-locus gene sequence data presented here are a significant step towards an improved future understanding of the molecular evolution of Tricyrtis via multi-locus evaluation.