The diversity of <i>Ficus</i>

BACKGROUND: The influence of Ficus extends beyond its numbers (800 species), and fig trees are often key-stone species in their habitats. Ficus fills many tropical forest niches. The past 15 years have witnessed an explosion of research in Ficus, and its obligate mutualists in the chalcid family Agaonidae, but also on its wider community of interactants. Long-standing ideas have been challenged and pathways to speciation have been explored. We aim to stimulate collegiate discussion: why are there not more species of fig? SCOPE: Here we critically review the literature relating to diversification in Ficus, while presenting a synthetic overview of our current understanding and knowledge gaps. We illustrate key concepts with well-studied groups of Ficus and other obligate mutualisms. Our review is unapologetically detailed and includes extensive botanical insight that is frequently over-looked in the literature. We draw on these details to develop hypotheses relating to the origin of diversity within the genus Ficus. CONCLUSIONS: We argue that the fig itself represents a new niche and explore the implications of sexual and vegetative traits in driving diversification (species richness) and diversity (in the ecological sense). An increasingly stable backbone phylogeny and the availability of genomic nuclear and chloroplast data has shed dappled light upon the deep evolutionary past. Incidences of potential diversification through introgression exist, but we must be cautious as the tools used were not always suitable for revealing ancient hybridization. An asymmetric genetic sampling of figs and wasps has further influenced our concepts of host specificity in the genus. Our comparative approach evaluates classical models of speciation in Ficus, concluding that adaptive radiations on islands have triggered diversification. We should maintain global research networks and sample widely. It is tempting to over generalise results. This leads to misconceptions and missing puzzle pieces. Further, adopting standard protocols ensures connectivity.