Evolutionary history of ferns and lycophytes: aligning molecular divergence time estimates with the global fossil record in amber

• Applicant: Dr. Ledis Regalado
• Subject Area: Palaeontology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 450754641

DNA-based divergence time estimates suggest that, although ferns and lycophytes are ancient groups of vascular spore plants, several extant lineages are relatively young having arisen following the emergence of angiosperm-dominated forests in the Cretaceous. Prominent examples are ferns of the order Polypodiales (representing 66% of the extant fern diversity), and most of the extant subgenera of the lycophyte species-rich genus Selaginella. However, the previous fossil record of ferns suggests that the Cretaceous fern flora was dominated by early diverging leptosporangiate lineages, including Osmundales, Cyatheales, Gleicheniales, Salviniales, and Schizaeales but Polypodiales are exceedingly rare. Likewise, the fossil record of Selaginellales for this period has been scarce. DNA-based divergence time estimates also inferred that modern tropical rain forest establishment in the Cenozoic triggered an epiphytic fern and lycophyte radiation. This epiphytic diversification has been inferred to be synchronous with the Paleocene/Eocene thermal maximum, followed by a diversification in the Oligocene and Miocene.Three major amber deposits (Burmese, Dominican and Mexican) provide windows to these crucial intervals. This project aims to evaluate and use new amber inclusions of ferns and lycophytes from the Cretaceous and Miocene to test (1) the predicted dominance of Polypodiales in the Cretaceous; (2) the rapid diversification of at least six of the seven extant subgenera of Selaginella by the Early Cretaceous; and (3) the presence of a rich fern and lycophyte epiphytic community in Miocene tropical forests. These predictions will be tested through an interdisciplinary approach combining morphological studies, phylomorphospace exploration and ancestral state reconstructions of morphological characters in molecular phylogenies of worldwide taxa of relevant groups. Next-generation sequencing (NGS) of whole chloroplast genomes (plastomes) will be used to resolve phylogenetic relationships within target datasets. The utility of the newly discovered fossils for establishing robust time-calibrated phylogenies will also be tested. This project is the first of its kind to study fossils of three-dimensionally preserved ferns and lycophytes from two crucial time horizons for which amber provides an excellent window to the past. It will provide a comprehensive picture of these groups as components of tropical Cretaceous and Miocene forests. As a result of this project, our understanding of evolution for the fern and lycophyte tree of life will be significantly improved.

• DFG Programme: Research Grants
• International Connection: China
• Cooperation Partners: Professor Dr. Harald Schneider; Professor Dr. Bo Wang