Abstract
The antennae of mosquitoes are model systems for acoustic sensation, in that they obey general principles for sound detection, using both active feedback mechanisms and passive structural adaptations. However, the biomechanical aspect of the antennal structure is much less understood than the mechano-electrical transduction. Using confocal laser scanning microscopy, we measured the fluorescent properties of the antennae of two species of mosquito—Toxorhynchites brevipalpis and Anopheles arabiensis—and, noting that fluorescence is correlated with material stiffness, we found that the structure of the antenna is not a simple beam of homogeneous material, but is in fact a rather more complex structure with spatially distributed discrete changes in material properties. These present as bands or rings of different material in each subunit of the antenna, which repeat along its length. While these structures may simply be required for structural robustness of the antennae, we found that in FEM simulation, these banded structures can strongly affect the resonant frequencies of cantilever-beam systems, and therefore taken together our results suggest that modulating the material properties along the length of the antenna could constitute an additional mechanism for resonant tuning in these species.
Highlights
The exquisite sensitivity of animal sensory organs has been noted many times [1,2,3,4,5,6]
Using confocal laser scanning microscopy, we measured the fluorescent properties of the antennae of two species of mosquito—Toxorhynchites brevipalpis and Anopheles arabiensis—and, noting that fluorescence is correlated with material stiffness, we found that the structure of the antenna is not a simple beam of homogeneous material, but is a rather more complex structure with spatially distributed discrete changes in material properties
The flagellum consists of 13 segments, each of which, except the first that articulates in the pedicel and cannot be observed directly, has a blue ring followed by a yellowreddish arrowhead or coronal structure that appears to be more sclerotized
Summary
The exquisite sensitivity of animal sensory organs has been noted many times [1,2,3,4,5,6]. While knowledge of mechanical behaviour, for some sensory organs, has increased in the last decade [7], rather little is known about the material composition and properties underlying these complex behaviours in terms of the geometry-defining distribution of stresses and strains within the sensor [7]. The pedicel houses some 16 000 sensory neurons [14], the majority of which are used for acoustic detection. These neurons connect to radially distributed prongs, attaching the neurons to the base of the flagellum. The flagellum itself is the physical sensor—it consists of 13 sequential flagellomeres that project distally These act as viscosity sensors, undergoing oscillatory displacement in the presence of
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