Abstract
Differential phase optical low coherence reflectometry (OLCR) was used to detect sub-wavelength displacements in the infrared-sensitive thoracic pit organ of Melanophila acuminata (Coleoptera: Buprestidae) upon absorption of infrared radiation at 3.39 μm. The displacement had more complex morphology but similar amplitude (∼100 nm at 1 W cm −2) when compared to the displacement measured from the exocuticle in an alternate region on the beetle's body. In addition, a simplified finite difference model was developed to predict the temperature distribution and resultant thermal expansion in the pit organ tissue. The experimental and model results were interpreted to help clarify the mechanism by which the sensilla in the pit organ convert infrared radiation to neural signals. The results of this paper are discussed in relation to the photo-thermal–mechanical transduction hypothesis. This is the first experimental examination of the transduction mechanism in Melanophila acuminata.
Highlights
Several recent reports have described electrophysiological experiments performed on the infrared (IR) sensitive beetle Melanophila acuminata (Coleoptera: Buprestidae) (Schmitz and Bleckmann, 1998; Hammer et al, 2001a)
The results described are the first experimental examination of the transduction mechanism in Melanophila acuminata
The sub-wavelength displacement measured by interferometric means is the first experimental investigation of the mechanism by which the pit organ of the beetle Melanophila acuminata converts infrared radiation to neural signals
Summary
Several recent reports have described electrophysiological experiments performed on the infrared (IR) sensitive beetle Melanophila acuminata (Coleoptera: Buprestidae) (Schmitz and Bleckmann, 1998; Hammer et al, 2001a). Investigators have described the ultrastructure of the pit organ responsible for IR detection (Vondran et al, 1995; Schmitz and Bleckmann, 1997). Investigators have hypothesized that the mechanism of transduction from infrared radiation to neural signal takes place, in part, by mechanical means (Vondran et al, 1995; Schmitz and Bleckmann, 1998). According to this photo-thermal– mechanical hypothesis, infrared energy is absorbed by the spherule, which produces a thermal expansion. Examination of the material properties and spectral sensitivity of the organ has provided evidence of correlation between the sen-
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