Meeting Abstract
Chameleons lack a tympanum, but two chameleon species have co-opted their pterygoid plate to serve as a receptor for airborne sound via a connection between this plate and the extracolumella. We hypothesize that the pterygoid plate of these “hearing” chameleons has adaptations that would improve its sound reception function. We expected that the pterygoid plate would exhibit more negative allometry in “hearing” chameleons than in “non-hearing” ones, as negative allometry is common in sensory structures. We also hypothesized that the porosity of the plate would be lower in “hearing” chameleons, reducing the structure’s acoustic impedance. We measured basal skull length and pterygoid plate area in chameleon skulls and fitted the measurements to an allometric growth curve. We also µ-CT scanned dry skulls and used CT-An to measure porosity of the plate. We used dissections to identify a connection between the pterygoid plate and extracolumella in four additional species, indicating that this hearing method has evolved at least three times independently. Our preliminary allometry results show that the pterygoid plate has more positive allometry in “hearing” species. This could indicate that chameleons never reach a body size that would allow their plate to be large enough to optimally capture the frequencies they need to hear. Equally surprising was the preliminary result that “hearing” chameleons have a plate with about half the porosity of “non-hearing” ones. This could serve to give the structure a higher resonant frequency in “hearing” species. Overall, our results do suggest that “hearing” chameleons have subtle modifications in their pterygoid plate compared to other species. We intend to explore the acoustic consequences of these modifications through modeling.
