PARENT SESSION

RIB MORPHOLOGY OF BATS IN RELATION TO THE POWER OF BIOSONAR VOCALIZATIONS. Winston C. Lancaster¹, M. Brock Fenton², Judith Eger³ and Matina Kalcounis-Rüppell⁴. ¹ California State University, Sacramento, Sacramento, CA; ² University of Western Ontario, London; ³ Royal Ontario Museum, Toronto; ⁴ University of North Carolina at Greensboro, Greensboro, NC.

ABSTRACT- Great interspecific variations in the widths of ribs and intercostal muscle spaces have been described, but neither quantified, nor related to behavior. The ribs and associated musculature function both in respiration and vocalization, and we suggest that a stiffer ribcage may be an adaptive advantage for the production of high-energy biosonar calls. Therefore, we investigated the morphology of the ribs in bats in relation to energetic characteristics of biosonar vocalization. We examined the axial skeletons of 56 species of bats from 13 families. We measured total length of the rib cage, cranio-caudal diameter of each rib, and forearm length of one randomly selected, articulated specimen per species. Measurements were used to calculate the proportion of the rib cage composed of intercostal space. Power of biosonar vocalizations was categorized using unpublished data and descriptions from the literature. Categories of power of biosonar vocalizations were: no biosonar (NA); low duty cycle/low intensity (d/i); low duty cycle/high intensity (d/I); high duty cycle/high intensity (D/I). We found that some bats have narrow ribs with wide intercostal spaces, in contrast to other species that have broad ribs with narrow intercostal spaces. Ignoring phylogenetic affiliations, we found a significant relationship between intercostal space and categories of biosonar. Specifically, bats that use D/I calls have rib cages with significantly wider ribs and narrower intercostal spaces in contrast to non-echolocating bats. Bats that use d/i and d/I calls have intercostal spaces of intermediate width. However, when we controlled for phylogenetic affiliations in our analyses, both by adding family into the model and by examining variation within families, these differences were not apparent. Our results suggest that there is no relationship between morphology and echolocation type that is independent of phylogeny. Our result may be affected by small samples from diverse families; increased sampling may reveal a significant relationship between intercostal space and power of biosonar vocalizations.

KEY WORDS: rib morphology, biosonar vocalizations , bats