Meeting Abstract

126.6  Tuesday, Jan. 7 15:00  Diversity and functional consequences of reducing synovial joints in bat wings BAHLMAN, J*; LIPPE, H; BREUER, K; SWARTZ, S; University of British Columbia; Brown University; Brown University; Brown University batman@zoology.ubc.ca

Bat wings, like other mammalian limbs, contain many joints within the digits. These joints collectively affect dynamic 3D wing shape, thereby affecting the amount of aerodynamic force a wing can generate. Bats are a speciose group, and show substantial variation in the number of wing joints. Additionally, some bat species have joints with extensor but not flexor muscles. While numerous studies have examined the diversity in number of joints and presence of muscles, musculoskeletal variation in the digits has not been interpreted in phylogenetic, functional, or ecological contexts. To provide this context, we quantify the number of joints and the presence/absence of muscles for 44 bat species, and map them phylogenetically. We show that, relative to the ancestral state, joints and muscles were lost and regained multiple times in many lineages and on different digits. Comparison of species with contrasting feeding ecologies demonstrates that those that feed primarily on non-mobile food (e.g. fruit) have fewer fully active joints than species that catch mobile prey (e.g. insects). We hypothesize a functional tradeoff between energetic savings and maneuverability. Having fewer joints reduces the mass of the wing, thereby reducing the energetic requirements of flapping flight. The presence of more joints increases the spectrum of possible 3D wing shapes, potentially enhancing the range and fine control of aerodynamic force production and maneuverability.