A FUNCTIONAL DESIGN SPACE FOR AERODYNAMIC DISPERSAL BEHAVIOR BASED ON WING MORPHOLOGY FOR ALL LIVING AND FOSSIL PLANT PROPAGULES

Seed dispersal is an important life history trait in plants, impacting local ecology as well as large scale macroecological and macroevolutionary processes. Understanding how plant traits influence dispersal processes is an integral step to understanding dispersal potential of past plant populations and predicting dispersal patterns in current populations. One of the most prevalent types of dispersal is wind dispersal, having evolved many times across land plants. Although different structures have evolved to enhance wind dispersal in plants, one of the most effective modifications is attachment of a wing. Wings are effective over a broad range of seed sizes and can lead to complex aerodynamic behaviors, acting to slow descent and/or increase lateral displacement of falling seeds.

Winged seeds are present in at least 160 extant families and ~800 genera. Even with this taxonomic diversity, a small subset of morphological characters is shared across the majority of all winged forms that can be used to summarize form and predict aerodynamic behavior(s). These characters were used to create a morphospace within which both extant and extinct propagule forms can be placed. The plotting of 276 extant genera resulted in clear clustering of taxa and well-defined unoccupied regions of the morphospace. Propagule drops performed with 104 extant genera revealed that these distinct clusters corresponded to general aerodynamic behaviors. These patterns suggest large-scale trends common to all winged propagules defined by optimization of biomechanical properties for the reliable performance of specific dispersal behaviors.

Because areas of morphospace correspond to specific classes of aerodynamic behavior, the inclusion of fossils allows for the prediction of aerodynamic behavior of extinct forms. Thus, broad evolutionary patterns of dispersal ecology become traceable through the fossil record. An analysis of Paleozoic taxa revealed a very different pattern of morphospace occupation than observed in extant taxa. For the first 70 million years of their history, winged propagules only occupied a small subset of the morphologies and aerodynamic behaviors observed in extant taxa, indicating possible taxonomic or environmental limitations during the earliest chapter of winged propagule evolution.