First plastid phylogenomic study reveals potential cyto-nuclear discordance in the evolutionary history of Ficus L. (Moraceae).

ABSTRACT

Standard Sanger chloroplast markers provide limited information to resolve species level relationships within plants, in particular within large genera. Figs (Ficus L., Moraceae) compose one of the 50 largest genera of angiosperms with ∼750 species occurring in the tropics and subtropics worldwide. Figs, in addition to being a keystone food resource in rainforests, are well-known for the mutualistic interactions with their pollinating wasps. It is regarded as a model system for understanding co-evolution dating back more than 75million years. However, despite significant taxon sampling, combinations of low copy nuclear, nuclear ribosomal and chloroplast regions have not been able to confidently resolve relationships among major groups of figs. Using a high throughput sequencing approach we attempted to resolve the major lineages of Ficus based on plastome data. In this study, we show that the use of a de novo assembled plastome from within the genus provides less ambiguity and higher coverage across the 59 Ficus and 6 outgroup plastome assemblies compared to using the nearest available reference plastome outside the genus resulting in improved resolution and higher support of the phylogenetic relationships within Ficus inferred from plastome data. Chloroplast genome data confidently resolved relationships among major groups of figs and largely support current understanding based on nuclear sequence data including passively pollinated Neotropical section Pharmacosycea as sister lineage to all other Ficus. However, conflicts between the new plastome topology and previous nuclear studies are observed for both individual species as well as relationships among some sections at deeper levels. Conflicts could be caused by lack of resolution in the nuclear data or may indicate potential cyto-nuclear discordance as previously observed in an African lineage of Ficus.