A trip to a grocery store exposes us to an outstanding diversity of fruits. While this variety was influenced by human selection during plant domestication, it mainly reflects strategies of seed dispersal that evolved over millions of years. Despite the huge variation in fruit color, shape, and size, common patterns can still be identified, especially the repeated evolution of fleshy fruits (e.g. olives, apples, tomatoes). Though this pattern is well observed, we are still exploring the role of different factors and their selective pressures. These can be intrinsic, as evolution of inherited genes determining fruit traits, or extrinsic, as the environment.
FRUITFUL dissected the evolution of fleshy fruits in the olive family (Oleaceae). Within its ca. 700 species, multiple lineages independently evolved fleshy fruits and species live in a variety of environments. Through this project, we built a new phylogenetic framework of Oleaceae, and updated the taxonomy of several of its lineages, we identified independent transitions to fleshy fruit within the family and estimated the historical biogeography of the groups within the family.
With a new phylogeny for Oleaceae, based on cytoplasmic and nuclear information, we showed that the five tribes (Myxopyreae, Fontanesieae, Forthythieae, Jasmineae and Oleeae) are well supported and monophyletic, with Jasmineae clearly sister to Oleeae. We also show that the four Oleeae subtribes (Schreberinae, Ligustrinae, Fraxininae, Oleinae) are well defined.
The phylogenetic framework in Oleaceae was further revised by updates to the taxonomy of the Notelaea and Schreberinae clades. For Notelaea, we re-circumscribed the genus and updated species names. For the Schreberinae tribe, we proposed a complete incorporation of Comoranthus species into Schrebera.
Using the updated phylogenetic framework and a database of fruit types, we showed that the ancestral state for fruit type in Oleaceae is a dry, dehiscent fruit (i.e. a dry fruit that opens when mature). We also found that several transitions towards fleshy, indehiscent fruits happened throughout the family's evolutionary history. Further, we showed that the intermediate state between a dry, dehiscent fruit, and a fleshy, indehiscent one, is a dry, indehiscent fruit. This means that anatomically-speaking, fruits first change their dehiscence (from dehiscent to indehiscent), and then change the state of their fruit wall (from dry to fleshy).
Finally, the biogeography of some Oleaceae’s clades is very complex, with groups succeeding to reach far-away regions in the world. For instance, we showed that species of the Notelaea clade are distributed today in very segregated parts of the world as Australasia, the Hawaiian Islands, Macaronesia, and the Mediterranean Region. This group originated most likely in Eurasia during the Early Miocene, and to reach some of the farther regions they most likely had birds as dispersers for their fleshy fruits.
