The genus Rena includes over 100 species. The true frogs of genus Rana are widely inhabited in both New and Old World, and are mainly found in the northern hemisphere, e.g., Asia, Europe, North America and north of South America. As the model animals which are commonly applied in behavior, development, genetics, physiology, ecology and evolution, these species have received extensive attentions. Moreover, the various habitats of these species also provide optimistic materials in carrying out large-scaled studies on biogeography and diversifications. However, difficulties, e.g., their intercontinental dispersal, conservation concern, threats of extinction, etc, have hindered the progresses of these studies. Some earlier results were even misinterpreted by inaccurate phylogeny of these groups. Therefore, it is critical to systematically build the evolutionary relationships of genus Rena.

Recently, an “Out of Asia” theory regarding the origination and diversification of Rena was proposed in a joint study conducted by more than ten researchers from America, Europe and Asia. It was described that genus Rena originated in the East Asia region, perhaps in southwest of China, and this “Out of Asia” pattern involved two independent dispersals of Rana from East Asia to North America via Beringian land bridge and a third one into Europe and Central Asia.

In this study, to minimize sampling bias, 91 species of the 101 currently recognized Rena were included, covering all the major lineages. By analyzing three fragments of mitochondrial DNA (mtDNA) and six nuclear DNA (nuDNA) loci of the samples, a comprehensive and well-resolved phylogeny for the genus Rena was yielded. Then, the group’s diversification and global biography was clarified. The results indicate significant differences in the diversification among the species of the New world and Old World. For example, the more species-rich lineage of New World Rana appears to have experienced a rapid radiation following its colonization of the New World, especially with its expansion into montane and tropical areas of Mexico, Central America, and South America, whereas, Old World Rana exhibited very slow diversification and later underwent a distinct increase in speciation rate.

In summary, the most important contribution of this recent study is that it re-built our understanding on the evolution and diversification patterns of the well studied genus Rena, which was severely been misled by morphological homoplasy and plesiomorphic color patterns, as well as a reliance primarily on mitochondrial genes. The comprehensive and time-calibrated phylogeny constructed in this study regarding the genus Rana throughout Eurasia and the Americas will surely benefic lots of future related studies.

The main findings of this study have been published on Systematic Biology.