Dissertation Research: Phylogenetics of Derived Leptosporangiate Ferns: A Reassessment of the Polypodiaceae S. L.

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

0073036 Schmid, Smith, and Cranfill Graduate student Raymond Cranfill, under the direction of Drs. Rudolf Schmid and Alan Smith, proposes to study the evolutionary history of derived leptosporangiate ferns, the Polypodiales, through use of both molecular sequence data and morphology. The Polypodiales comprise most of the ferns living today and number about 8,000-10,000 species. They are a conspicuous and diverse element of almost every ecosystem in the wetter tropics and subtropics, as well as some temperate ecosystems. Although we now know that this group is monophyletic (that is, with a single presumed ancestry), our understanding of interrelationships within the Polypodiales is poor and unreliable. This is particularly true for the least specialized or basal groups that were the first to evolve. The evolutionary radiation of the Polypodiales probably occurred over a very short time in the Cretaceous Period, which occurred 140-65 million years ago. Because the diversification apparently was rapid at a relatively distant geological time, we will need to examine several different genes from the chloroplast, mitochondrion, and nucleus, as well as morphological features, in order to define the deeper relationships between these ferns. An understanding of the explicit evolutionary relationships of the Polypodiales is important for several reasons. (1) Because this is the most diverse group of extant ferns, an understanding of these relationships promises to shed light on a range of different and interesting topics in evolutionary and structural biology, from macroevolutionary processes to evolutionary transformations in morphological characters. (2) A fresh understanding of the latter is particularly important to developmental biologists who are interested in the genetic control of developmental processes in plants. (3) This research is also important to our understanding of the evolution of modern terrestrial and epiphytic (non-terrestrial) ecosystems. It appears that the Polypodiales may have radiated contemporaneously with the flowering plants and perhaps in response to habitat diversification that occurred as the flowering plants radiated into a wide variety of habitats and began to form communities of greater ecological complexity than may have existed before. Comparable processes appear to be shaping similar patterns of diversity. Therefore, what we learn from ferns may contribute significantly to an understanding of the early evolution and development of plant communities that we see today.