title: Testing hypotheses of bat baculum function with 3D models derived from microCT.
abstract: The baculum (os penis) has been extensively studied as a taxon-specific character in bats and other mammals but its mechanical function is still unclear. There is a wide consensus in the literature that the baculum is probably a sexually selected character. Using a novel approach combining postmortem manipulation and three-dimensional (3D) imaging, we tested two functional hypotheses in the common noctule bat Nyctalus noctula, the common pipistrelle Pipistrellus pipistrellus, and Nathusius' pipistrelle Pipistrellus nathusii: (i) whether the baculum can protect the distal urethra and urethral opening from compression during erection and copulation; and (ii) whether the baculum and corpora cavernosa form a functional unit to support both the penile shaft and the more distal glans tip. In freshly dead or frozen and thawed bats, we compared flaccid penises with artificially 'erect' penises that were inflated with 10% formalin. Penises were stained with alcoholic iodine and imaged with a lab-based high-resolution x-ray microtomography system. Analysis of the 3D images enabled us to compare the changes in relative positions of the baculum, corpora cavernosa, urethra, and corpus spongiosum with one another between flaccid and 'erect' penises. Our results support both functional hypotheses, indicating that the baculum probably performs two different roles during erection. Our approach should prove valuable for comparing and testing the functions of different baculum morphologies in bats and other mammals. Moreover, we have validated an essential component of the groundwork necessary to extend this approach with finite element analysis for quantitative 3D biomechanical modeling of penis function.
authors: Department of Theoretical Biology, University of Vienna, Vienna, Austria.
authors: Anna Nele
authors: AN
authors: Herdina
authors: Diane A
authors: DA
authors: Kelly
authors: Helena
authors: H
authors: Jahelková
authors: Peter H C
authors: PH
authors: Lina
authors: Ivan
authors: I
authors: Horáček
authors: Brian D
authors: BD
authors: Metscher
mesh_terms: D000818:Animals; D002685:Chiroptera / Q000033:anatomy & histology / Q000502:physiology*; D021621:Imaging, Three-Dimensional; D008297:Male; D010410:Penile Erection / Q000502:physiology*; D010413:Penis / Q000033:anatomy & histology* / Q000502:physiology; D055114:X-Ray Microtomography
keywords: 3D model; Chiroptera; functional morphology; iodine stain; micro-CT; penis bone; x-ray microtomography
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