Connectivity patterns of the hindlimb musculoskeletal system in living and fossil diving birds

Abstract

To study the hindlimb connectivity patterns of aquatic birds, we compared the musculoskeletal multi-networks of non-divers (Numididae and Anatidae), wing-propelled divers (Alcidae and Sphenicidae), and foot-propelled divers (Anhingidae, Phalacrocoracidae, Podicipedidae, and Gaviidae). Anatomical multi-networks are undirected multigraphs where bones and muscles were considered as nodes and the physical junctions between them as links. From each network we calculated different parameters, performed a principal component analysis and constructed a phylomorphospace. Our results show that both phylogenetic history and locomotor habits contributed to shape the musculoskeletal hindlimb connectivity of aquatic birds. Wing-propelled divers have complex and dense networks and are separated from the rest of birds, with penguins tightly clustered together. Non-divers and foot-propelled divers have loose networks and are clustered together, except for Podicipedidae and Gaviidae that are clustered together but separated from the rest. We also compared the networks of extant and fossil diving taxa and observed that complete muscular reconstructions can be compared with extant taxa, which is useful in order to include paleontological information in analyses of musculoskeletal disparity. These results encourage the exploration of the musculoskeletal connectivity patterns in other locomotor modules and taxa of different habits, in order to explore the relative contribution of ecology and phylogeny in the evolution of the connectivity of the musculoskeletal system, and to asses some generalities about the connectivity of musculoskeletal system in highly specialized taxa.