Hybridization, apomixis and polyploidy as evolutionary drivers of the maidenhair fern family (Pteridaceae) in the West Indies

Interspecific hybridization and polyploidization are widely recognized as major drivers of fern evolution. The combination of these processes can explain most of the phenotypic variation observed in extant species, particularly in closely related species complexes. Additionally, nearly 10% of ferns for which the reproductive mode has been determined exhibit apomixis, suggesting that this form of asexuality also plays an important role in fern evolution. Recent global analyses of polyploid biogeography have revealed high levels of polyploidy in several island systems, indicating a significant contribution of this evolutionary process to the diversification of established island lineages.

Adiantum deltoideum 1

The main goal of this project is to investigate the role of polyploidy, hybridization, and apomixis in the formation of endemic fern flora across an island system with a highly heterogeneous origin and geological complexity, such as the West Indies. This region is renowned for its considerable number of endemic species, which account for approximately 40% of the local fern flora. It has been postulated that the fern flora in question resulted from a combination of immigration events from adjacent regions of tropical America and local speciation processes, particularly in the Greater Antilles. However, the processes that lead to the formation of these endemic lineages remain unexplored.

The study model will be the family Pteridaceae, which is particularly well-suited to the study of such phenomena, especially some genera, such as Adiantum, Adiantopsis, Notholaena, and Pityrogramma. The extent to which hybridization, polyploidization, and apomixis have contributed to speciation in those groups will be assessed through a phylogenomic approach, which will encompass a broad sampling of the geographical range and morphological variation of the target groups. A combination of target enrichment (hybrid capture) and plastome sequencing will be employed. These data will be complemented by morphological, cytological, and reproductive mode data to complete an integrative assessment of these speciation events. Finally, the expanded sampling will allow us to conduct new dating and biogeographic analyses, thereby providing a historical context for the testing of hypotheses regarding the origin, distribution, and duration of polyploid and apomictic fern lineages in the West Indies.

PIs: Ledis Regalado, Marc Appelhans