A molecular phylogeny of the Pacific clade of Cyrtandra (Gesneriaceae) reveals a Fijian origin, recent diversification, and the importance of founder events
Cyrtandra (Gesneriaceae) is among the largest genera of flowering plants in the remote oceanic islands of the Pacific, with an estimated 175 species distributed across an area that extends from the Solomon Islands, east to the Marquesas Islands, and north to the Hawaiian Islands. The vast majority of species are single-island endemics that inhabit upland rainforests. Although previous molecular phylogenetic studies greatly advanced our understanding of the diversification of Pacific Cyrtandra, a number of uncertainties remain regarding phylogenetic relationships, divergence times, and biogeographic patterns within this large and widely dispersed group. In the present study, five loci (ITS, ETS, Cyrt1, psbA-trnH, and rpl32-trnL) were amplified and sequenced for phylogenetic reconstruction of 121 Cyrtandra taxa. Maximum likelihood and Bayesian inference confirmed that C. taviunensis from Fiji is sister to the remaining members of the Pacific clade. Dating analyses and ancestral area estimation indicates that the Pacific clade of Cyrtandra originated in Fiji during the Miocene ca. 9 mya. All major crown lineages within the Pacific clade appeared < 5 mya, coincident with the emergence of numerous Pacific islands and a subsequent increase in available habitat. The biogeographic history of Cyrtandra in the Pacific has been shaped by extinction, dispersal distance, and founder events. Six founder events each from Fiji and Samoa resulted in the broad distribution of Cyrtandra seen in the Pacific today. Biogeographic stochastic mapping analyses suggest that cladogenesis within Pacific Cyrtandra was exclusively the result of founder events. A mean of 25 founder events was recovered between Pacific archipelagos, while a mean of 10 founder events was recovered within the Hawaiian archipelago.
