Fig trees, belonging to the genus Ficus in the Moraceae family, are known for their remarkable diversity, with over 850 species. To uncover the evolutionary secrets behind this diversity, an international team of researchers, including a plant biologist from Northwestern University, conducted a study analyzing 1,858 genes from 520 fig species. Recently published in the Proceedings of the National Academy of Sciences, the study challenges the previous hypothesis that widespread gene sharing among fig species drove their evolution, suggesting instead that it only played a modest role.
The researchers discovered a pattern of stable evolution within fig lineages, punctuated by occasional instances of gene sharing across species. This finding contradicts the notion that introgression, the transfer of genes between related species through hybridization, was a major driver of fig diversity. The unique pollination process of figs, with each species relying on a specific fig wasp species for pollination, had led to the hypothesis that pollinator switching and subsequent hybridization were key factors in driving fig diversity. However, the new study indicates that fig tree evolution followed a more consistent and tree-like pattern.
The study also examined the relationship between fig trees and their specialized pollinators, the fig wasps of the Agaonidae family. The researchers observed that local hybridization does not always result in gene transfer across lineages in plants, particularly when there are obligate plant-pollinator relationships. This analysis sheds light on the role of hybridization and co-diversification with fig wasp pollinators in the evolution and diversification of fig trees.
Nyree Zerega, a Northwestern botanist and co-author of the study, emphasized the significance of these findings for understanding fig tree evolution. Zerega, who directs the Program in Plant Biology and Conservation at Northwestern in collaboration with the Chicago Botanic Garden, described the study as a game changer, providing valuable insights and an evolutionary roadmap for future research on this important group of plants.
Source: Northwestern University