Transcriptome analysis of two radiated species and the subsequent species delimitation of the complex.

PREMISE

is an important gymnosperm genus, and the most diverse of all cycad genera. The complex of species are morphologically similar and difficult to distinguish due to a lack of genomic resources.

METHODS

We characterized the transcriptomes of two closely related and endangered species endemic to Hainan, China: and . Three single-copy nuclear genes in the complex were sequenced based on these transcriptomes, enabling us to evaluate the species boundaries using the multispecies coalescent method implemented in the Bayesian Phylogenetics and Phylogeography program.

RESULTS

We obtained 68,184 and 81,561 unigenes for and s, respectively. We identified six positively selected genes that are mainly involved in stimulus responses, suggesting that environmental adaptation may have played an important role in the relatively recent divergence of these species. The similar distribution peaks at 1.0 observed for the paralogs in the two species indicate a common whole-genome duplication event. Our species delimitation analysis indicated that the complex consists of three distinct species, which correspond to the previously reported morphological differences.

DISCUSSION

Our study provides valuable genetic resources for species and guidance for the taxonomic treatment of the complex, as well as new insights into evolution of species within .