My recent work has raised a number of intriguing questions. Although we have documented a large range of variation in mineralization in bat wing bones, the precise nature of the mechanical consequences of this variation remains unknown. I am now actively collecting precise, detailed measurements of material properties from bones from diverse North American bat species, and will 1) demonstrate clearly the relationship between mineralization and mechanical characteristics, and 2) extend the taxonomic diversity of our study sample, thereby also testing for variation among taxa in mechanical characteristics of the skeleton, with particular attention to variation in body size, wing shape/flight mode, and phylogenetic affinity.
To fully understand the loads exerted on wings during natural flight behaviors, we must better understand the role of the wing membrane in exerting and transmitting force during flight. In the future, I will pursue this avenue through a series of projects to be carried out in collaboration with Philip Watts from the California Institute of Technology. We plan to begin studies of wing shape and membrane tension in flight in bats trained to fly in wind tunnels. We will apply stereophotogrammetric techniques to document the wing's three-dimensional configuration and to monitor membrane strain through the wingbeat cycle. These data will serve as critical inputs for further refinement of our computer model of bat flight, and will allow us to more rigorously test its validity for biologically realistic situations.
With a well-validated model in hand, I plan to investigate more deeply a number of issues in the comparative biology of bat flight and morphology. Our model will be able to realistically predict joint, bone, and membrane forces at key anatomical locations; by varying the wing morphology, wing loading, flight speed, distribution of wing forces, etc., we will be able to model how these forces change with biologically relevant variation in body mass, wing shape, and flight mode. These model results can then be interpreted in part by reference back to real morphologies observed within the diversity of extant bats. This information, along with my ongoing efforts to collect precise measurements of wing bone shape in several hundred bat species, will allow me to carry out in-depth historical analysis of wing morphology and flight behavior in bats. This work will be carried out in part in collaboration with Dr. Nancy Simmons, Assistant Curator, Department of Mammals, American Museum of Natural History, a world authority on phylogenetic relationships within bats and of bats to other mammals. We propose together to map phylogenetically the evolution of bat wings, combining the insights from my laboratory's biomechanical analyses and Dr. Simmons ground-breaking phylogenetic analyses to produce a novel understanding of character evolution and the diversification of flight.
These studies have significance beyond bettering our knowledge of how the mammalian skeleton has been co-opted for flight within a single monophyletic lineage. I seek to understand design features in a way that produces results that may be generalized; issues of trade-offs between design for maximizing strength and minimizing weight are important far beyond bats. I hope that as we continue to unravel the nature and diversity of the chiropteran flight apparatus we will continue to gain insights that can extend beyond the particulars of this model system.
