Resolving a paradox of global botanical biodiversity: Why is Africa the “odd man out?”
Emily Sessa
Understanding how plant diversity has arisen over time, and how and why plants are distributed across the planet as they are, has been a major goal of biodiversity science since Darwin’s time. A particularly striking feature of global plant distributions is that sub-Saharan Africa has many fewer plant species than comparable tropical regions in Asia and the Americas, which is known as the “odd man out” biogeographic pattern. This research will investigate the possible causes of the odd man out pattern by investigating the evolutionary history of ferns. Ferns are an ancient plant group that occupy diverse ecosystems globally. Consequently, they are ideal models for understanding the roles of extinction, speciation and migration in generating the modern-day flora of sub-Saharan Africa. Broader impacts of the project will build research capacity among early career scientists, including post-doctoral fellows, graduate and undergraduate students at the University of Florida and strengthen biodiversity science education within diverse K-12 and college classrooms. Project personnel will develop a study-abroad undergraduate course in southern Africa, engage middle school teachers in developing K-12 lesson plans, and build both web-based and hands-on modules for public outreach about plants and biodiversity science.
Researchers will uncover the evolutionary and biogeographic history of three fern genera (Dryopteris, Cheilanthes, Polystichum) that are widespread in African, Asian and the American continents to investigate the genesis of the odd man out biogeographic pattern. Species will be sampled in the field and from herbaria; DNA sequence data from approximately 450 nuclear markers will be used to generate their phylogenies. The resulting phylogenies will be used to reconstruct historical biogeographic movements of over 1000 species, calculate diversification rates, and determine whether shifts in ancestral ecological niche envelopes correlate with migration events or changes in diversification rate. Ancestral climate reconstructions and trait data from common garden experiments will be co-analyzed to understand how climate may have shaped traits and diversification patterns over time. The project will generate new data resources and specimens for broad dissemination and build cross-institutional collaborations. These outcomes will advance the research as well as fuel future discoveries at the intersection of fern systematics, historical biogeography and biodiversity science.