Mulple Origins of a High Force Feeding System in Waterfowl AARON M. OLSEN, MARK W. WESTNEAT Abstract University of Chicago, Field Museum of Natural History Results Convergent biomechanical systems offer unique insight into musculoskeletal systems because the Geese have origins across the anseriform phylogeny Geese have evolved a higher force feeding system repeated associaon of structure and funcon by independent evoluonary events constutes Grazing requires more force than dabbling strong evidence for adaptaon. Owing to their great diversity, feeding systems are ideal for  feed primarily by dabbling, which involves rapid moon of the bill through water or mud idenfying convergent systems. We collected beak shape data from 32 genera within the order to filter out food parcles , which includes ducks, geese, and mergansers. We find that the beak  Geese feed primarily by grazing, which involves cung tough vegetaon at the p of the bill shape and the associated foraging behavior, grazing, have evolved mulple mes from a -like  Thus, grazing likely requires a more force-advantaged system relave to dabbling ancestor. Differences in beak shape and other predictors of relave bite force indicate that the evoluon of a goose-shaped beak is associated with the evoluon of a higher bite force. By Beak Depth:Length Increases with Bite Force Higher Beak Depth to Length Rao idenfying aspects of the musculoskeletal system that are shared among goose feeding systems  The rao of beak depth to beak length has we can beer understand how bones, muscles and joints adapt to producing and sustaining been shown to increase with the evoluon higher forces. G. fuliginosa (5 N) of higher bite forces in Darwin’s Finches (Figure 7, le; Herrel et al. 2005; Grant & Geese Duck Grant 2003) Introducon Ducks Anseriforms can be divided into three foraging groups, based on diet and beak shape (Fig. 1).  A similar paern is observed in the Pursuit diver G. fors (17 N) evoluon of geese from a duck-like Outgroups DABBLERS MALLARD ancestor (Fig. 7, right) • Filters food from ANAS PLATYRHYNCHOS water with rapid, Higher Beak Effecve Mechanical Advantage connuous moon 1 cm G. magnirostris (71 N) Goose  Effecve mechanical advantage (EMA) of bill measures the force advantage of a lever Figure 7. Beak depth:length increases with bite my.opera.com/RobinL (Westneat 2003) force (shown in newtons) in Darwin’s Finches. A  Geese have beaks with a significantly similar paern is seen in ducks and geese. PURSUIT DIVERS RED-BREASTED MERGANSER higher EMA relave to ducks (Fig. 8) • Consume fish diving MERGUS SERRATOR Lower Inlever-Outlever Rao below the surface 1 cm • The rao of inlever to outlever length (Fig. 2) influences the force advantage of a 4-bar linkage • A shorter inlever relave to outlever ( i.e. lower rao) produces a force-advantage system • The 4-bar linkage of geese has a significantly lower rao relave to that of ducks (Fig. 9) Craig Nash Effecve Mechanical Advantage of Beak Kinemac Inlever-Outlever Rao GRAZERS/BROWSERS UPLAND GOOSE Tree: Fulton et al. 2012; Hacke et al. 2008; Eo et al. 2008; Sorenson et al. 1999; Non-Geese • Diet is primarily CHLOEPHAGA PICTA Geese Srami et al. 1996; Livezey 1986 t-test terrestrial 1 cm t-test Figure 5. Supertree of 52 Anseriform genera. Representaves of several goose lineages at right. p-value = 0.0003 vegetaon Non-Geese p-value = 0.002  Geese do not form a monophylec group within Anseriforms (Fig. 5) Geese 

4freephotos.com The simplest explanaons for the distribuon of geese across the anseriform phylogeny are: Figure 1. Examples of major foraging behaviors among anseriforms (1) mulple origins of geese from a duck-like ancestor, or (2) a greater number of mulple origins of ducks from a goose-like ancestor Anseriforms in different foraging categories differ not only in beak shape but in overall cranial shape as well. Parcularly structures in the skull associated with beak movements. Anseriforms Geese have evolved independently from a duck-like ancestor can move both their lower and upper Pterygoid bill. However, no muscles insert Palane  Ancestral state reconstrucon of upper beak shape supports mulple origins of geese and a single origin of pursuit divers from a duck-like ancestor (Fig. 6) directly onto the upper bill. Instead, Cranium muscles pull on the quadrate, Figure 9. Geese have cranial linkages with a Upper bill Figure 6. Morphospace Figure 8. Geese have beaks with a significantly pterygoid, jugal and palane (Fig. 2), Evoluon of beak shapes in Anseriforms significantly lower inlever-outlever rao. (Outlever) of upper beak shapes in higher EMA relave to non-geese. which trasmit force to the upper bill, Anseriforms. Morpho- causing it to rotate. In engineering, space supports this closed loop of kinec bones is Discussion Quadrate Jugal common division of  Mulple origins of geese are supported by ancestral state reconstrucon of upper beak shape known as a linkage. Upper bill shape (Inlever) anseriforms into geese, is a good predictor of foraging  Since the sister group to anseriforms (Galliformes) and the sister group to all other anseriforms Figure 2. The cranial linkage bones cause upper bill rotaon ducks and piscivorous category and both beak shape and pursuit divers. Arrows (Chauna; Fig. 5) have galliform-like beaks, the ancestor of all anseriforms was likely galliform-like linkage geometry predict how force producon varies across anseriforms. summarize results of  Although both galliforms and geese are terrestrial herbivores, they have disnct beak shapes: PC2 ancestral state (1) Geese have a broad beak p like ducks, while the beak p of galliforms is pointed Methods reconstrucon which (2) Goose beaks are intermediate in height between galliforms and ducks (Fig. 6) supports at least three  That geese have a similar diet to galliforms but yet share aspects of beak shape with ducks Our study includes a total of 79 specimens represenng 32 independent origins of suggests that these beak features are remnants retained in geese from a duck-like ancestor genera within Anseriformes. Morphological landmarks were geese (dashed lines) obtained using a custom stereo camera setup (Fig. 3) and from a duck-like  Differences in diet, beak shape and key aspects of the beak musculoskeletal system are all direct linear transformaon for reconstrucng 3D points from ancestor. PC1 consistent with the evoluon of higher bite forces as geese evolved from duck-like ancestors mulple camera views (Fig. 4; Miller et al. 1980). Upper bill (1) The evoluon of grazing from dabbling is expected to increase bite force morphology was characterized by fing 3D curves to the (2) Anseriform beak shape evoluon parallels higher bite force evoluon in Darwin’s finches tomium and culmen. An anseriform supertree was prepared Figure 3. Two camera stereo setup (3) Differences in the lever and linkage geometry of geese indicate that geese are significantly by combining several phylogenies (sources listed in Fig. 5). Literature cited Acknowledgments beer than non-geese at amplifying force from cranial musculature to the beak p An upper beak morphospace plot (Fig. 6) was prepared by performing PC analysis on Procrustes • Eo, Sh et al. Zoologica Scripta 38, 5 (2008). Thanks to David Willard, Ben superimposed landmarks and curves. Tiled background images of beaks in Figure 6 show the • Hacke, SJ et al. Science, 320 (2008). Marks and Mary Hennen at the changes in upper beak shape associated with the first two principal components (PC). • Sorenson, MD et al. Proc. R. Soc. Lond. B, 266 (1999). Field Museum of Natural History Conclusion • Fulton, TL et al. Proc. R. Soc. Lond. B, 279 (2012). for collecon assistance. We thank Geese have convergently evolved beaks that generate higher forces during feeding. Idenfying The evoluonary trajectories of anseriforms • Srami, M et al. Australian Journal of Zoology, 44 (1996). the Dept of Organismal Biology aspects of the musculoskeletal system that are shared among goose feeding systems will inform through upper beak morphospace • Livezey, BC. The Auk, 103 (1986). and Anatomy at the University of our understanding of how bones, muscles and joints adapt to producing and sustaining higher (summarized in Fig. 6) were determined by • Westneat, MW. Journal of Theorecal Biology, 223 (2003). Chicago, the Carol Schneider Fund, forces. In vivo bite force data from geese would be useful in confirming higher bite forces in ancestral state reconstrucon (Felsenstein • Herrel, A et al. J. Evol. Biol., 18 (2005). NSF GRFP, NSF grant DEB 0844745 geese. Also, nothing is known of how beak movements differ among geese or between ducks 1985) without branch lengths. PC1 and PC2 • Grant, RB & Grant, PR. BioScience, 53 (2003). and NSF IGERT DGE-0903637 for and geese. Lastly, connued research into beak evoluon across the addional 32 orders of scores were used as states in the ancestral • Miller, NR et al. J Biomechanics, 13 (1980). financial support. will likely reveal addional convergent feeding systems that will provide rich insight into how state reconstrucon. Figure 4. 3D Landmark and curve reconstrucon • Felsenstein, J. The American Naturalist, 125 (1985). diverse musculoskeletal systems funcon and evolve.